tag:theconversation.com,2011:/africa/topics/aerodynamics-4305/articlesAerodynamics – The Conversation2024-02-09T00:36:19Ztag:theconversation.com,2011:article/2228532024-02-09T00:36:19Z2024-02-09T00:36:19ZHigher, faster: what influences the aerodynamics of a football?<figure><img src="https://images.theconversation.com/files/573580/original/file-20240203-27-i63qjv.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C5472%2C3579&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">In addition to a player's ability to throw it, a number of factors will influence a ball's flight, including its size, inflation pressure and texture.</span> <span class="attribution"><span class="source">(Shutterstock)</span></span></figcaption></figure><p>With <a href="https://www.nfl.com/news/super-bowl-lvii-averages-audience-of-113-million-viewers-fox-sports">113 million viewers in the United States</a> and 40 million more around the world, the Super Bowl is the most popular sports event in North America. This year’s event on Sunday – with the added attraction of a <a href="https://www.cnn.com/videos/sports/2024/02/06/super-bowl-players-vegas-taylor-swift-wire-nc-vpx.cnn">romance in the spotlight</a> – promises to attract as many fans.</p>
<p>In Canada, the most recent Grey Cup final, last November, reached a <a href="https://twitter.com/RDS_RP/status/1726722586816430330">record audience</a> of 3.7 million viewers who tuned in to watch the Montréal Alouettes’ victory.</p>
<p>The two leagues definitely don’t enjoy the same popularity – far from it. Nor do they have the same rules. But there is another difference: although similar in appearance, the famous oval balls used in football have specific characteristics on both sides of the border that can affect their aerodynamics, i.e. the forces exerted by the air on the ball during its flight. The design and characteristics of the ball have an impact on the magnitude of these forces.</p>
<p>It might be news to football players, but their talent for throwing balls long distances is not the only thing that matters. A number of factors affect the ball’s aerodynamics, including the way it is made and its inflation pressure.</p>
<p>As a professor in the Department of Mechanical Engineering at Québec’s École de technologie supérieure, I am interested in experimental fluid dynamics. I study the physics of fluid flows and certain applications (e.g. propulsion of aquatic vehicles, aerodynamic applications). Fluid dynamics is a vast field and affects many aspects of our lives, such as the flow of blood in the heart, the flight of aircraft, the beautiful swirling patterns in Jupiter’s atmosphere or the perfect football pass for a touchdown.</p>
<h2>Ball size affects flight stability</h2>
<p>The NFL and CFL have the same <a href="https://cfldb.ca/faq/equipment/#:%7E:text=The%20CFL%20football%20dimensions%20are,to%2028%201%2F2%20inches">rules</a> regarding the dimensions of their balls. They must be between 11" and 11.25" long. They must also be inflated to between 12.5 psi and 13.5 psi, giving them a maximum circumference of between 28" and 28.5" around the length and between 21" and 21.25" around the width.</p>
<p>These dimensions are important. The football acts like a gyroscope. The higher the speed of rotation, the more stable the ball will be during its flight. Different dimensions can therefore have specific effects on the stability of the ball’s flight.</p>
<figure class="align-center ">
<img alt="An American football player catches a ball in mid-flight on a field" src="https://images.theconversation.com/files/573219/original/file-20240203-25-y5at9n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/573219/original/file-20240203-25-y5at9n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=438&fit=crop&dpr=1 600w, https://images.theconversation.com/files/573219/original/file-20240203-25-y5at9n.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=438&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/573219/original/file-20240203-25-y5at9n.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=438&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/573219/original/file-20240203-25-y5at9n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=551&fit=crop&dpr=1 754w, https://images.theconversation.com/files/573219/original/file-20240203-25-y5at9n.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=551&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/573219/original/file-20240203-25-y5at9n.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=551&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The size of the football matters. The ball acts like a gyroscope. The higher the speed of rotation, the more stable the ball will be during its flight.</span>
<span class="attribution"><span class="source">(Shutterstock)</span></span>
</figcaption>
</figure>
<p>A larger circumference suggests that more of the ball’s mass is located away from its centre line. This means that it will have a higher moment of inertia (resistance to rotation) and, therefore, that the same force applied to make it rotate will result in a lower speed of rotation.</p>
<h2>Two stripes and laces make a difference</h2>
<p>While there are two white stripes on the Canadian ball, as well as laces, American rules don’t mention these.</p>
<p>The differences between the Canadian and American balls can have an effect on their drag. A drag force is the resistance to a moving object in a fluid. In this case, it is mainly the resistance caused by the air (a fluid), which is called form or pressure drag.</p>
<p>Let’s take the example of a golf ball. Its dimples encourage turbulence, which allows the airflow to stick to the ball and reduce its total drag. Less drag means the ball can fly further with the same force applied.</p>
<p>The laces on a football and any other significant modification to its surface (a logo, a valve), in combination with the rotation of the ball, will to some extent have the same effect. It would be interesting to study how <a href="https://www.engineering.com/story/the-aerodynamics-of-a-football">these differences</a> between NFL and CFL footballs affect their respective drag.</p>
<h2>NFL or CFL, which ball is better?</h2>
<p>To do this, we could use a wind tunnel (an experimental installation in the form of a tunnel with a controlled airflow) to simulate the movement of air (fluid flow) around the two balls that will be fixed in space, put into rotation and subject to an airflow speed that would imitate the balls’ speed of flight.</p>
<p>An aerodynamic force balance could be used to measure the differences in drag between the two balls subjected to the same conditions. Ideally, to eliminate other factors of variability, the two balls would have the same dimensions.</p>
<p>The passage of air around the ball could be visualized using smoke or particle image/tracking velocimetry. The latter is a method in which the air is seeded with particles (helium-filled soap bubbles or oil droplets). The movement of these particles could then be captured using a camera to quantify the airspeed at all points around the ball. This would allow regions of flow separation and recirculation to be seen, and provide an idea of the distribution of aerodynamic forces around the ball.</p>
<figure class="align-center ">
<img alt="A gloved hand holds a football on a grassy surface" src="https://images.theconversation.com/files/573221/original/file-20240203-21-3s2qf1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/573221/original/file-20240203-21-3s2qf1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/573221/original/file-20240203-21-3s2qf1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/573221/original/file-20240203-21-3s2qf1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/573221/original/file-20240203-21-3s2qf1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=424&fit=crop&dpr=1 754w, https://images.theconversation.com/files/573221/original/file-20240203-21-3s2qf1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=424&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/573221/original/file-20240203-21-3s2qf1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=424&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A ball about to be kicked. A number of factors will influence the aerodynamics of the ball.</span>
<span class="attribution"><span class="source">(Shutterstock)</span></span>
</figcaption>
</figure>
<p>Different rotation speeds and flight speeds could be examined, as there is always the possibility of developing flow instabilities, which would lead to a change in its behaviour around the ball. </p>
<p>This would help determine whether the NFL or CFL ball is better.</p>
<h2>Ball texture influences drag</h2>
<p>There is another type of drag, this one attributable to the friction between the air and the surface of the ball. This is called friction drag.</p>
<p>It depends mainly on the texture of the ball and its speed. The rougher the texture of the ball, the greater the friction drag for the same speed. Similarly, a faster ball speed will have a higher friction drag.</p>
<p>By reducing the form drag, we further reduce the total drag of the ball, which can therefore go further and faster on the football field.</p>
<h2>And then there’s the weather!</h2>
<p>The weather also plays a role in the aerodynamics of the football.</p>
<p>Cold or hot temperatures can affect the size of the ball by reducing or increasing the air pressure inside it.</p>
<p>Similarly, temperature can have some effect on the material properties of the ball, with colder temperatures making it stiffer and warmer temperatures making it softer.</p>
<p>Temperature and humidity also play a role in the physical properties of air, altering its density and viscosity.</p>
<p>Rain will also directly affect drag as, in a sense, it affects the texture of the ball’s surface as felt by the air.</p>
<p>But that won’t be an issue in Las Vegas on Feb. 11 for the Super Bowl game, since Allegiant Stadium is covered.</p><img src="https://counter.theconversation.com/content/222853/count.gif" alt="La Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Giuseppe Di Labbio ne travaille pas, ne conseille pas, ne possède pas de parts, ne reçoit pas de fonds d'une organisation qui pourrait tirer profit de cet article, et n'a déclaré aucune autre affiliation que son organisme de recherche.</span></em></p>A football’s dimensions, pressure and texture affect its aerodynamics, i.e. the forces exerted by the air on the ball as it flies.Giuseppe Di Labbio, Professeur adjoint, École de technologie supérieure (ÉTS)Licensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1945852022-11-18T13:33:32Z2022-11-18T13:33:32ZWorld Cup: This year’s special Al Rihla ball has the aerodynamics of a champion, according to a sports physicist<figure><img src="https://images.theconversation.com/files/496003/original/file-20221117-11-u1q60v.jpg?ixlib=rb-1.1.0&rect=27%2C192%2C4210%2C2814&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Every World Cup, Adidas introduces a new ball, and this year's is called the Al Rihla.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/official-adidas-al-rihla-balls-pictured-during-the-fifa-u-news-photo/1435761267?phrase=Adidas%20Al%20Rihla&adppopup=true">Joern Pollex/FIFA via Getty Images</a></span></figcaption></figure><p>As with every World Cup, at the <a href="https://www.fifa.com/fifaplus/en/tournaments/mens/worldcup/qatar2022">2022 FIFA World Cup</a> in Qatar the players will be using a new ball. The last thing competitors want is for the most important piece of equipment in the most important tournament in the world’s most popular sport to behave in unexpected ways, so a lot of work goes into making sure that every new World Cup ball feels familiar to players.</p>
<p><a href="https://scholar.google.com/citations?user=eHzYy_EAAAAJ&hl=en&oi=ao">I am a physics professor</a> at the <a href="https://www.lynchburg.edu/">University of Lynchburg</a> who studies the physics of sports. Despite controversies over corruption and human rights issues surrounding this year’s World Cup, there is still beauty in the science and skill of soccer. As part of my research, every four years I do an analysis of the new World Cup ball to see what went into creating the centerpiece of the world’s most beautiful game.</p>
<h2>The physics of drag</h2>
<p>Between shots on goal, free kicks and long passes, many important moments of a soccer game happen when the ball is in the air. So one of the most important characteristics of a soccer ball is how it travels through air.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/495997/original/file-20221117-24-elfah2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A ball against a gray background with dust showing air coming off the top and bottom of the ball." src="https://images.theconversation.com/files/495997/original/file-20221117-24-elfah2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/495997/original/file-20221117-24-elfah2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/495997/original/file-20221117-24-elfah2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/495997/original/file-20221117-24-elfah2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/495997/original/file-20221117-24-elfah2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=565&fit=crop&dpr=1 754w, https://images.theconversation.com/files/495997/original/file-20221117-24-elfah2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=565&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/495997/original/file-20221117-24-elfah2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=565&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">At low speeds, the air will only hug the surface of the front half of a soccer ball before peeling off in an organized way called laminar flow, as seen here in this wind tunnel photo.</span>
<span class="attribution"><span class="source">John Eric Goff</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>As a ball moves through air, a thin layer of mostly still air called the boundary layer surrounds some part of the ball. At low speeds this boundary layer will only cover the front half of the ball before the flowing air peels away from the surface. In this case, the wake of air behind the ball is somewhat regular and is called laminar flow. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/495998/original/file-20221117-13-jzu9ro.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A ball in wind tunnel with the air flow nearly going completely around a ball." src="https://images.theconversation.com/files/495998/original/file-20221117-13-jzu9ro.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/495998/original/file-20221117-13-jzu9ro.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/495998/original/file-20221117-13-jzu9ro.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/495998/original/file-20221117-13-jzu9ro.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/495998/original/file-20221117-13-jzu9ro.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=565&fit=crop&dpr=1 754w, https://images.theconversation.com/files/495998/original/file-20221117-13-jzu9ro.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=565&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/495998/original/file-20221117-13-jzu9ro.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=565&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">At high speeds, the air flowing over a soccer ball will almost travel completely to the back of the ball before separating into chaotic swirls called turbulent flow.</span>
<span class="attribution"><span class="source">John Eric Goff</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>When a ball is moving quickly, though, the boundary layer wraps much farther around the ball. When the flow of air does eventually separate from the ball’s surface, it does so in a series of chaotic swirls. This process is called turbulent flow.</p>
<p>When calculating how much force moving air imparts on a moving object – called drag – physicists use a term called the drag coefficient. For a given speed, the higher the drag coefficient is, the more drag an object feels.</p>
<p>It turns out that a soccer ball’s drag coefficient is <a href="https://doi.org/10.1177/1754337118773214">approximately 2.5 times larger for laminar flow than for turbulent flow</a>. Though it may seem counterintuitive, roughening a ball’s surface delays the separation of the boundary layer and keeps a ball in turbulent flow longer. This fact of physics – that rougher balls feel less drag – is the reason dimpled golf balls fly much farther than they would if the balls were smooth.</p>
<p>When it comes to making a good soccer ball, the speed at which the air flow transitions from turbulent to laminar is critical. This is because when that transition occurs, a ball begins to slow down dramatically. If laminar flow starts at too high a speed, the ball begins to slow down much more quickly than a ball that maintains turbulent flow for longer.</p>
<h2>Evolution of the World Cup ball</h2>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/496001/original/file-20221117-17-aotl08.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A black and white soccer ball made of hexagonal and pentagonal panels." src="https://images.theconversation.com/files/496001/original/file-20221117-17-aotl08.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/496001/original/file-20221117-17-aotl08.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=617&fit=crop&dpr=1 600w, https://images.theconversation.com/files/496001/original/file-20221117-17-aotl08.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=617&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/496001/original/file-20221117-17-aotl08.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=617&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/496001/original/file-20221117-17-aotl08.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=776&fit=crop&dpr=1 754w, https://images.theconversation.com/files/496001/original/file-20221117-17-aotl08.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=776&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/496001/original/file-20221117-17-aotl08.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=776&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The Adidas Telstar, featured in the 1970 and 1974 World Cups, is what many people imagine when they think of a soccer ball.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/shine2010/4171467954/">shine2010</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Adidas has supplied balls for the World Cup since 1970. Through 2002, each ball was made with the iconic 32-panel construction. The 20 hexagonal and 12 pentagonal panels were traditionally made of leather and stitched together.</p>
<p>A new era began with the 2006 World Cup in Germany. The 2006 ball, called the Teamgeist, consisted of 14 smooth, synthetic panels that were <a href="https://soccerballworld.com/official-world-cup-final-match-ball-teamgeist-soccer-ball/">thermally bonded</a> together instead of stitched. The tighter, glued seal kept water out of the interior of the ball on rainy and humid days.</p>
<p>Making a ball out of new materials, with new techniques and with a smaller number of panels, changes how the ball flies through the air. Over the past three World Cups, Adidas tried to balance the panel number, seam properties and surface texture to create balls with just the right aerodynamics.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/496002/original/file-20221117-20952-htnf4k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A soccer ball sitting on a stand." src="https://images.theconversation.com/files/496002/original/file-20221117-20952-htnf4k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/496002/original/file-20221117-20952-htnf4k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/496002/original/file-20221117-20952-htnf4k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/496002/original/file-20221117-20952-htnf4k.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/496002/original/file-20221117-20952-htnf4k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/496002/original/file-20221117-20952-htnf4k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/496002/original/file-20221117-20952-htnf4k.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The smoother Jabulani ball from the 2010 South Africa World Cup received a lot of criticism for being slow in the air.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/the-jabulani-soccer-ball-which-was-the-official-ball-of-the-news-photo/1040917924?phrase=adidas%20jabulani&adppopup=true">Picture Alliance via Getty Images</a></span>
</figcaption>
</figure>
<p>The eight-panel Jabulani ball in the 2010 South Africa World Cup had textured panels to make up for shorter seams and a fewer number of panels. Despite Adidas’ efforts, the Jabulani was a <a href="https://www.nydailynews.com/sports/official-world-cup-ball-jabulani-blame-soft-goals-robert-green-missed-article-1.182196">controversial ball</a>, with many players complaining that it decelerated abruptly. When my colleagues and I analyzed the ball in a wind tunnel, we found that the <a href="https://doi.org/10.1177/1754337114526173">Jabulani was too smooth overall</a> and so had a higher drag coefficient than the 2006 Teamgeist ball.</p>
<p>The World Cup balls for Brazil in 2014 – the Brazuca – and Russia in 2018 – the Telstar 18 – both had six oddly shaped panels. Though they had slightly different surface textures, they had generally the same overall surface roughness and, therefore, <a href="https://doi.org/10.1177/1754337118773214">similar aerodynamic properties</a>. Players generally <a href="https://www.insidescience.org/news/new-2018-world-cup-ball-passes-wind-tunnel-tests">liked the Brazuca</a> and Telstar 18, but some complained about the tendency of <a href="https://www.express.co.uk/sport/football/975257/World-Cup-Telstar-18-match-balls-burst-Lionel-Messi">the Telstar 18 to pop easily</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/495999/original/file-20221117-14-xqlwae.jpg?ixlib=rb-1.1.0&rect=77%2C23%2C1919%2C1245&q=45&auto=format&w=1000&fit=clip"><img alt="A soccer player looks at a ball in the air." src="https://images.theconversation.com/files/495999/original/file-20221117-14-xqlwae.jpg?ixlib=rb-1.1.0&rect=77%2C23%2C1919%2C1245&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/495999/original/file-20221117-14-xqlwae.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=388&fit=crop&dpr=1 600w, https://images.theconversation.com/files/495999/original/file-20221117-14-xqlwae.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=388&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/495999/original/file-20221117-14-xqlwae.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=388&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/495999/original/file-20221117-14-xqlwae.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=487&fit=crop&dpr=1 754w, https://images.theconversation.com/files/495999/original/file-20221117-14-xqlwae.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=487&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/495999/original/file-20221117-14-xqlwae.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=487&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">France’s Kylian Mbappe is one of the many soccer stars who will be playing with the new Al Rihla ball at the 2022 Qatar World Cup.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/frances-forward-kylian-mbappe-eyes-the-ball-during-a-news-photo/1244853336?phrase=fifa%20world%20cup%20ball&adppopup=true">Franck Fife via Getty Images</a></span>
</figcaption>
</figure>
<h2>2022’s Al Rihla ball</h2>
<p>The new Qatar World Cup soccer ball is the Al Rihla. </p>
<p>The Al Rihla is made with <a href="https://www.fifa.com/tournaments/mens/worldcup/qatar2022/media-releases/al-rihla-by-adidas-revealed-as-fifa-world-cup-qatar-2022-tm-official-match">water-based inks and glues</a> and contains 20 panels. Eight of these are small triangles with roughly equal sides, and 12 are larger and shaped sort of like an ice cream cone. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/495996/original/file-20221117-14-gkrh90.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A closeup of the Al Rihla ball showing small dimples and divots in the surface." src="https://images.theconversation.com/files/495996/original/file-20221117-14-gkrh90.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/495996/original/file-20221117-14-gkrh90.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/495996/original/file-20221117-14-gkrh90.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/495996/original/file-20221117-14-gkrh90.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/495996/original/file-20221117-14-gkrh90.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=565&fit=crop&dpr=1 754w, https://images.theconversation.com/files/495996/original/file-20221117-14-gkrh90.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=565&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/495996/original/file-20221117-14-gkrh90.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=565&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">To make the Al Rihla rougher and more aerodynamic, Adidas put small divots into the surface.</span>
<span class="attribution"><span class="source">John Eric Goff</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Instead of using raised textures to increase surface roughness like with previous balls, the Al Rihla is covered with <a href="https://www.fifa.com/tournaments/mens/worldcup/qatar2022/media-releases/al-rihla-by-adidas-revealed-as-fifa-world-cup-qatar-2022-tm-official-match">dimplelike features</a> that give its surface a relatively smooth feel compared to its predecessors.</p>
<p>To make up for the smoother feel, the Al Rihla’s seams are wider and deeper – perhaps learning from the mistakes of the overly smooth Jabulani, which had the shallowest and shortest seams of recent World Cup balls and which many players felt was slow in the air.</p>
<p>My colleagues in Japan tested the four most recent World Cup balls in a wind tunnel at the <a href="http://www.global.tsukuba.ac.jp/">University of Tsukuba</a>. </p>
<p><iframe id="XP7Ka" class="tc-infographic-datawrapper" src="https://datawrapper.dwcdn.net/XP7Ka/5/" height="400px" width="100%" style="border: none" frameborder="0"></iframe></p>
<p>When air flow transitions from turbulent to laminar flow, the drag coefficient rises rapidly. When this happens to a ball in flight, the ball will suddenly experience a steep increase in drag and slow down abruptly.</p>
<p>Most of the World Cup balls we tested made that transition at roughly 36 mph (58 kph). As expected, the Jubalani is the outlier, with a transition speed around 51 mph (82 kph). Considering that most free kicks start off traveling in excess of 60 mph (97 kph), it makes sense that players felt the Jabulani was slow and hard to predict. The Al Rihla has <a href="https://doi.org/10.1177/17543371221140497">aerodynamic characteristics very similar</a> to its two predecessors, and if anything, may even move a bit faster at lower speeds.</p>
<p>Every new ball is met with complaints from somebody, but the science shows that the Al Rihla should feel familiar to the players in this year’s World Cup.</p><img src="https://counter.theconversation.com/content/194585/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>John Eric Goff does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Adidas releases a new ball for every World Cup. At the highest level of play, a ball that behaves in unexpected ways can throw players off. A sports physicist explains the science of this year’s ball.John Eric Goff, Professor of Physics, University of LynchburgLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1764962022-02-09T18:47:03Z2022-02-09T18:47:03ZSki jump: Flying or falling with style?<figure><img src="https://images.theconversation.com/files/445195/original/file-20220208-21-nw1u31.jpg?ixlib=rb-1.1.0&rect=122%2C73%2C3432%2C2629&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Ski jumpers use aerodynamics and physics to overcome gravity -- at least for a while</span> <span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/APTOPIXGermanySkiJumpingFourHills/2b64f1bcbdc14400ac611acdff71c0f5/photo?Query=ski%20jump&mediaType=photo&sortBy=&dateRange=Anytime&totalCount=21735&currentItemNo=97">AP Photo/Matthias Schrader</a></span></figcaption></figure><p>If you or I jump in the air as high as possible, we can stay off the ground for about half a second. Michael Jordan could stay aloft for <a href="https://www.scienceabc.com/pure-sciences/secret-michael-jordan-slam-dunks-basketball-math-physics-hang-time-jump.html">almost one second</a>. While there are many events at the Winter Olympics that feature athletes performing feats of athleticism and strength while high in the air, none <a href="https://www.youtube.com/watch?v=WhVLgTsoMhQ">blur the line between jumping and flying</a> quite as much as the ski jump.</p>
<p>I teach students about the <a href="https://www.clemson.edu/science/departments/physics-astro/people/profiles/amyj">physics of sports</a>. The ski jump is perhaps one of the most intriguing events in the Winter Games to showcase physics in action. The winner is the athlete who travels the farthest and who flies and lands with the best style. By turning their skis and bodies into what is essentially a wing, ski jumpers are able to fight gravity and stay airborne for five to seven seconds as they travel about the <a href="https://olympics.com/beijing-2022/olympic-games/en/results/ski-jumping/results-women-s-nh-individual-fnl-0002sj-.htm">length of a football field</a> through the air. So how do they do this? </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/445189/original/file-20220208-32038-db77yy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A person flying with a red triangular hang glider." src="https://images.theconversation.com/files/445189/original/file-20220208-32038-db77yy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/445189/original/file-20220208-32038-db77yy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/445189/original/file-20220208-32038-db77yy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/445189/original/file-20220208-32038-db77yy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/445189/original/file-20220208-32038-db77yy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/445189/original/file-20220208-32038-db77yy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/445189/original/file-20220208-32038-db77yy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Hang gliders have large wings, are very aerodynamic and are very light, all of which maximize lift to produce long flights despite the lack of an engine.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Hanggliding_in_Sweden_2011.jpg#/media/File:Hanggliding_in_Sweden_2011.jpg">Gegik via WikimediaCommons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<h2>How to fly</h2>
<p>Three major concepts from physics are at play in the ski jump: gravity, lift and drag.</p>
<p>Gravity pulls any object in flight down toward the ground. Gravity acts on all objects equally and there is nothing athletes can do to lessen its effect. But the athletes also interact with the air as they move. It is this interaction that can produce lift, which is an upwards force produced by air pushing on an object. If the force produced from lift roughly balances the force of gravity, an object can glide or fly.</p>
<p>To produce lift, an object needs to be moving. As the object moves through the air, its surface collides with air particles and <a href="https://www.sciencedirect.com/topics/engineering/aerodynamic-lift">pushes these particles</a> out of the path of the object. As air particles are pushed down, the object is pushed up according to <a href="https://openstax.org/books/college-physics/pages/4-4-newtons-third-law-of-motion-symmetry-in-forces">Newton’s Third Law</a> of motion which says that for every action, there is an equal and opposite reaction. Air particles pushing an object upwards are what create lift. Increasing speed as well as increasing surface area will increase the amount of lift. The <a href="https://www.boeing.com/commercial/aeromagazine/aero_12/whatisaoa.pdf">angle of attack</a> – the angle of the object relative to the direction of air flow – can also affect lift. Too steep and the object will stall, too flat and it won’t push down on air particles. </p>
<p>While this all may seem complicated, sticking your hand out of a car window illustrates these principles perfectly. If you hold your hand perfectly flat, it will stay more or less in place. However, if you tilt your hand so that bottom is facing the direction of the wind, your hand will be pushed upwards as the air particles collide into it. That is lift.</p>
<p>The same collisions between an object and air that provide lift also produce <a href="https://physics.info/drag/">drag</a>. Drag resists the forward motion of any object and slows it down. As speed decreases, lift does too, limiting the length of a flight.</p>
<p>For ski jumpers, the goal is to use careful body positioning to maximize lift while reducing drag as much as possible.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/RHNPxhpH6qM?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">During excellent jumps, athletes will maximize lift and glide long distances.</span></figcaption>
</figure>
<h2>Flying on skis</h2>
<p>Skiers start high up on a slope then ski downhill to generate speed. They minimize drag by crouching down and carefully steer to reduce friction between the skis and ramp. By the time they reach the end they can be going <a href="https://ssec.si.edu/stemvisions-blog/falling-style-science-ski-jumping">60 miles per hour</a> (96kph).</p>
<p>The ramp ends at a takeoff point which, if you look closely, is actually at a slight downward <a href="http://www.skisprungschanzen.com/EN/Articles/0007-Ski+jumping+hill+dictionary">angle of 10 degrees</a>. Just before the athletes reach the end of the ramp, they jump. The ski landing slope is designed to mimic the path a jumper will take so that they are never more than <a href="https://assets.fis-ski.com/image/upload/v1639755981/fis-prod/assets/ICR_Ski_Jumping_2022_clean.pdf">10 to 15 feet</a> above the ground.</p>
<p>Once the athletes are in the air, the fun physics begins.</p>
<p>The jumpers do everything they can to produce as much lift as possible while minimizing drag. Athletes will never be able to generate enough lift to overcome gravity entirely, but the more lift they generate, the slower they will fall and the further down the hill they will travel. </p>
<p>To do this, athletes align their skis and body nearly parallel to the ground and place their skis in a V-shape just outside the form of the body. This position increases the surface area that generates lift and puts them in the ideal angle of attack that will also maximize lift. </p>
<p>As drag reduces the speed of the skier, lift decreases and gravity continues to pull on the jumper. Athletes will begin to fall faster and faster until they land.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/445194/original/file-20220208-32038-1ag0tph.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A ski jumper sitting on the start bench showing how it can be moved." src="https://images.theconversation.com/files/445194/original/file-20220208-32038-1ag0tph.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/445194/original/file-20220208-32038-1ag0tph.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/445194/original/file-20220208-32038-1ag0tph.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/445194/original/file-20220208-32038-1ag0tph.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/445194/original/file-20220208-32038-1ag0tph.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/445194/original/file-20220208-32038-1ag0tph.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/445194/original/file-20220208-32038-1ag0tph.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Many regulations – like the height of the starting point and ski length – are variable depending on conditions and the athlete’s height and weight.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Ski_jumping_at_the_2020_Winter_Youth_Olympics_-_20_January_2020_-_31.jpg#/media/File:Ski_jumping_at_the_2020_Winter_Youth_Olympics_-_20_January_2020_-_31.jpg">DarDarCH via WikimediaCommons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<h2>The rules follow the physics</h2>
<p>With so much physics at play, there are a lot of ways wind, equipment choices and even the athletes’ own bodies can affect how far a jump can go. So to keep things fair and safe, there are a <a href="https://www.fis-ski.com/en/inside-fis/document-library/ski-jumping-documents">lot of regulations</a>.</p>
<p>While watching the events, you may notice officials moving the starting point up or down the slope. This adjustment is made based on the wind speed as faster headwinds will produce more lift and result in longer jumps that could go past the safe landing zone.</p>
<p>Ski length is also regulated and tied to a skier’s height and weight. Skis can at most be <a href="https://assets.fis-ski.com/image/upload/v1544086634/fis-prod/Specifications_for_CC_JP_NC_SB_FS_FK_Competiton_Equipment.pdf">145% of the skier’s height</a> and skiers with a body mass index less than 21 must have shorter skis. Long skis are not always the best as the heavier the ski, the more lift you need to produce to stay airborne. Finally, skiers must <a href="https://assets.fis-ski.com/image/upload/v1623221580/fis-prod/assets/document-library/ski-jumping/Equipment-Guidelines.pdf">wear tight-fitting suits</a> to ensure that athletes will not use their clothing as an additional source of lift. </p>
<p>As you tune into the Olympics to marvel at the physical power of the athletes, take a moment to consider also their mastery of the concepts of physics.</p>
<p>[<em>Climate change, AI, vaccines, black holes and much more.</em> <a href="https://memberservices.theconversation.com/newsletters/?nl=science&source=inline-science-various">Get The Conversation’s best science and health coverage</a>.]</p><img src="https://counter.theconversation.com/content/176496/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Amy Pope does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Ski jumpers do everything they can to counteract the effects of gravity and fly as far as they can down hills.Amy Pope, Senior Lecturer of Physics and Astronomy, Clemson UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1759852022-02-04T19:59:53Z2022-02-04T19:59:53ZThe high-speed physics of how bobsled, luge and skeleton send humans hurtling faster than a car on the highway<figure><img src="https://images.theconversation.com/files/444394/original/file-20220203-19-xcns7h.jpg?ixlib=rb-1.1.0&rect=419%2C1373%2C2781%2C1718&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Bobsled, luge and skeleton athletes descend twisting, steep tracks at speeds upward of 80 mph (130 kmh).</span> <span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/VancouverOlympicsLuge/04f06c3e67b7419fb8c7501593eb84f9/photo?Query=luge%20olympic&mediaType=photo&sortBy=&dateRange=Anytime&totalCount=4131&currentItemNo=49">AP Photo/Sergey Ponomarev</a></span></figcaption></figure><p>Speed alone may be the factor that draws many sports fans to the <a href="https://www.beijing2022.cn/en/olympics_/bobsleigh.htm">bobsled, luge and skeleton events</a> at this year’s Beijing Winter Olympics. But beneath the thrilling descents of the winding, ice-covered track, a myriad of concepts from physics are at play. It is how the athletes react to the physics that ultimately determines the fastest runs from the rest of the pack.</p>
<p><a href="https://scholar.google.com/citations?hl=en&user=eHzYy_EAAAAJ">I study the physics of sports</a>. Much of the excitement of a luge run is easy to miss – the athletes’ movements are often too small to notice as they fly by looking like nothing more than a blur on your television. It would be easy to assume that the competitors are simply falling or sliding down a track at the whim of gravity. But that thought merely scratches the surface of all the subtle physics that go into a gold-medal-winning performance.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/444397/original/file-20220203-21-1bpy1ig.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An aerial view of a large twisting covered track." src="https://images.theconversation.com/files/444397/original/file-20220203-21-1bpy1ig.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/444397/original/file-20220203-21-1bpy1ig.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=306&fit=crop&dpr=1 600w, https://images.theconversation.com/files/444397/original/file-20220203-21-1bpy1ig.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=306&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/444397/original/file-20220203-21-1bpy1ig.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=306&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/444397/original/file-20220203-21-1bpy1ig.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=385&fit=crop&dpr=1 754w, https://images.theconversation.com/files/444397/original/file-20220203-21-1bpy1ig.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=385&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/444397/original/file-20220203-21-1bpy1ig.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=385&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Tracks for sliding events – like the Olympic track from the 2018 Pyeongchang Winter Olympics – drop hundreds of feet and feature many tight turns.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Olympic_Sliding_Centre#/media/File:Alpensia_20170202_05_(32619189236).jpg">Korean Culture and Information Service via Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-sa/4.0/">CC BY-NC-SA</a></span>
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</figure>
<h2>Gravity and energy</h2>
<p>Gravity is what powers the sleds down the ice-covered tracks in bobsled, luge and skeleton events. The big-picture physics is simple – start at some height and then fall to a lower height, letting gravity accelerate athletes to speeds <a href="https://www.si.com/olympics/2018/02/13/how-fast-does-luge-go-speed-velocity">approaching 90 mph</a> (145 kph). </p>
<p>This year’s races are taking place at the <a href="https://www.beijing2022.cn/en/olympics_/bobsleigh.htm">Yanqing National Sliding Center</a>. The track is roughly a mile long (1.6 km), drops 397 feet of elevation (121 meters) – with the steepest section being an incredible 18% grade – and <a href="https://www.ibsf.org/en/tracks/track/700012/Yanqing">comprises 16 curves</a>.</p>
<p>Riders in the sledding events reach their fast speeds because of the conversion of gravitational potential energy into kinetic energy. Gravitational potential energy represents stored energy and increases as an object is raised farther from Earth’s surface. The potential energy is converted to another form of energy once the object starts falling. Kinetic energy is the energy of motion. The reason a flying baseball will shatter the glass if it hits a window is that the ball transfers its kinetic energy to the glass. Both gravitational potential energy and kinetic energy increase as weight increases, meaning there is more energy in a four-person bobsled team than there is in a one-person luge or skeleton for a given speed.</p>
<p>Racers are dealing with a lot of kinetic energy and strong forces. When athletes enter a turn at 80 mph (129 kph) they experience accelerations that can reach <a href="https://www.technogym.com/us/newsroom/luge-courage-and-high-speeds/">five times that of normal gravitational acceleration</a>. Though bobsled, luge and skeleton may look easy, in reality they are anything but.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/444403/original/file-20220203-15-16gh0zf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A luge racer lying on his back in an aerodynamic pose." src="https://images.theconversation.com/files/444403/original/file-20220203-15-16gh0zf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/444403/original/file-20220203-15-16gh0zf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=460&fit=crop&dpr=1 600w, https://images.theconversation.com/files/444403/original/file-20220203-15-16gh0zf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=460&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/444403/original/file-20220203-15-16gh0zf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=460&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/444403/original/file-20220203-15-16gh0zf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=578&fit=crop&dpr=1 754w, https://images.theconversation.com/files/444403/original/file-20220203-15-16gh0zf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=578&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/444403/original/file-20220203-15-16gh0zf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=578&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Racers need to be as aerodynamic as possible to minimize drag and go faster.</span>
<span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/VancouverOlympicsLuge/7ae2fa592a92471387554d0f45f29ccf/photo?Query=luge%20olympic&mediaType=photo&sortBy=&dateRange=Anytime&totalCount=4131&currentItemNo=97">AP Photo/Ricardo Mazalan</a></span>
</figcaption>
</figure>
<h2>Aerodynamics</h2>
<p>Most tracks are around a mile long (1.6 km), and the athletes cover that distance in just under a minute. Final times are calculated by adding four runs together. The difference between the gold medal and silver medal in the men’s singles luge at the 2018 Winter Olympics <a href="http://www.fil-luge.org/cdn/uploads/lugmsingles-c73b2-1-0.pdf">was just 0.026 seconds</a>. Even tiny mistakes made by the best athletes in the world can cost a medal.</p>
<p>All the athletes start at the same height and go down the same track. So the difference between gold and a disappointing result comes not from gravity and potential energy, but from a fast start, being as aerodynamic as possible and taking the shortest path down the track. </p>
<p>While gravity pulls the athletes and their sleds downhill, they are constantly colliding with air particles that create a force called air drag, which pushes back on the athletes and sleds in a direction opposite to their velocity. The more aerodynamic an athlete or team is, the greater the speed.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/444401/original/file-20220203-15-1b14kwq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A team of bobsled racers going around a corner." src="https://images.theconversation.com/files/444401/original/file-20220203-15-1b14kwq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/444401/original/file-20220203-15-1b14kwq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=377&fit=crop&dpr=1 600w, https://images.theconversation.com/files/444401/original/file-20220203-15-1b14kwq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=377&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/444401/original/file-20220203-15-1b14kwq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=377&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/444401/original/file-20220203-15-1b14kwq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=473&fit=crop&dpr=1 754w, https://images.theconversation.com/files/444401/original/file-20220203-15-1b14kwq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=473&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/444401/original/file-20220203-15-1b14kwq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=473&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Bobsled teams must tuck themselves behind the leading edge of the sled to avoid the oncoming air.</span>
<span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/APTOPIXVancouverOlympicsBobsled/e41cf5b02a8b4a98ba1ad279d1c31190/photo?Query=bobsleigh%20olympic&mediaType=photo&sortBy=&dateRange=Anytime&totalCount=5034&currentItemNo=4">AP Photo/Andrew Medichini</a></span>
</figcaption>
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<p>To minimize drag from the air, luge riders – who are face up – lie as flat as possible. Downward-facing skeleton riders do the same. Whether in a team of two or four, bobsled riders stay tucked tightly inside the sled to reduce the area available for air to smash into. Any body positioning mistakes can make athletes less aerodynamic and lead to tiny increases in time that can cost them a medal. And these mistakes are tough to correct at the high accelerations and forces of a run.</p>
<h2>The shortest way down</h2>
<p>Besides being as aerodynamic as possible, the other major difference between a fast and a slow run is the path riders take. If they minimize the total length taken by their sleds and avoid zigzagging across the track, riders will cover less distance. In addition to simply not having to go as far to cross the finish line, shortening the path means facing less drag from air and losing less speed from friction with the track.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/444400/original/file-20220203-27-9hvavp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A skeleton racer running with his sled at the start of a race." src="https://images.theconversation.com/files/444400/original/file-20220203-27-9hvavp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/444400/original/file-20220203-27-9hvavp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/444400/original/file-20220203-27-9hvavp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/444400/original/file-20220203-27-9hvavp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/444400/original/file-20220203-27-9hvavp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/444400/original/file-20220203-27-9hvavp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/444400/original/file-20220203-27-9hvavp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Skeleton racers don’t have a means of directly controlling the runners, so they must use subtle body movements to flex the sled and initiate turns.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Nozomi_Komuro_start_LP_World_Cup_2017_(1_of_1).jpg#/media/File:Nozomi_Komuro_start_LP_World_Cup_2017_(1_of_1).jpg">121a0012 via Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Fans often miss the subtleties involved in turning and steering. The sleds for all the events sit on <a href="http://www.teamusa.org/%7E/media/USA_Luge/Documents/IRO_2014_AT_English.pdf">steel blades called runners</a>. Bobsleds have two sets of runners that make contact with the ice. The front rider pulls on <a href="https://www.rulesofsport.com/sports/bobsleighing.html">rings attached to pulleys that turn the front runners</a>. Runners on luge sleds have curved bows at the front where riders place their calves. By moving their head and shoulders or flexing their calves, athletes can turn the luge. Skeleton riders lack these controls and must <a href="http://www.ibsf.org/images/documents/downloads/2015_International_Rules_SKELETON.pdf">flex the sled</a> itself using their shoulders and knee to initiate a turn. Even a tiny head movement can cause the skeleton to move off the optimal path.</p>
<p>All of these subtle movements are hard to see on television, but the consequences can be large – oversteering may lead to collisions with the track wall or even crashes. Improper steering may lead to bad turns that cost riders time.</p>
<p>Though it may appear that the riders simply slide down the icy track at great speeds after they get going, there is a lot more going on. Viewers will have to pay close attention to the athletes on those fast-moving sleds to detect the interesting facets of physics in action.</p>
<p>[<em>Get fascinating science, health and technology news.</em> <a href="https://memberservices.theconversation.com/newsletters/?nl=science&source=inline-science-fascinating">Sign up for The Conversation’s weekly science newsletter</a>.]</p><img src="https://counter.theconversation.com/content/175985/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>John Eric Goff does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>It may look like athletes in bobsled, luge and skeleton simply grab a sled and hang on until the bottom, but high-speed physics and tiny motions mean the difference between gold and a crash.John Eric Goff, Professor of Physics, University of LynchburgLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1520222020-12-14T15:22:22Z2020-12-14T15:22:22ZSpaceX Starship prototype exploded, but it’s still a giant leap towards Mars<p>Private company SpaceX launched SN8, a prototype of its <a href="https://www.spacex.com/vehicles/starship/">Starship spacecraft</a>, designed to go to the Moon and Mars, on December 10. Its short flight attracted a great deal of attention <a href="https://www.theguardian.com/science/2020/dec/10/spacex-starship-sn8-explodes-on-landing-after-test-flight">for it’s final few seconds before landing</a> – when it exploded.</p>
<p>But consider the near perfect totality of its six-and-a-half-minute flight. Look at the groundbreaking technology and manoeuvres involved. It is reasonable to view this as a hugely successful test.</p>
<p>Ordinary spacecraft return to Earth by using the <a href="https://www.grc.nasa.gov/www/k-12/airplane/drag1.html">“aerodynamic drag”</a> in the atmosphere to slow their re-entry. Decelerating from 20,000 mph dissipates a lot of heat which is why they carry heat shields, and the final touchown is controlled by parachutes. The actual rocket engines don’t make a safe landing – they burn up and crash into the sea. </p>
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<p>This is a real waste of resources. SpaceX’s founder and CEO <a href="https://theconversation.com/elon-musk-biography-portrays-a-brutal-character-driven-by-lofty-dreams-41995">Elon Musk</a> is instead trying to reuse as much of the spacecraft as possible. If your ultimate destination is the Moon and onward to Mars, this makes a lot of sense because you can much more easily refuel at judicious locations along the way than build a new rocket.</p>
<p>Starship is a fully reusable rocket system designed to carry 100 tonnes of cargo into Earth orbit and beyond. It has a “booster” first stage which propels it into orbit and separates. The booster stage is designed to land safely and to be reused. SpaceX figured out how to do this with the <a href="https://theconversation.com/how-to-launch-a-rocket-into-space-and-then-land-it-on-a-ship-at-sea-57675">Falcon rocket</a>, but that’s only two thirds of the system. With Starship, the third of the system that helps propel the spacecraft further than Earth orbit is never ejected.</p>
<p>Landing the first stage booster is “easy” because it is ejected two minutes after launch and therefore returns to Earth from a relatively low altitude – never reaching super high speeds. NASA defines “high” hypersonic speed as a “Mach number” from 10 to 25. The booster only reaches about Mach 6.</p>
<p>Starship itself will be returning from orbit, reaching Mach 25. At this speed, the heat of reentry will melt the engines off. You therefore need a substantial heat shield which dissipates 99% of the energy – protecting the cargo and those all-important rockets that you need for landing. NASA’s partially reusable <a href="https://www.nasa.gov/mission_pages/shuttle/main/index.html">Space Shuttle</a> had huge wings used to glide the vehicle onto a runway. But wings are heavy and they reduce the potential payload capacity. Also, they won’t work on Mars or the Moon because there’s a lack of atmosphere – and runways.</p>
<h2>Belly-flop dynamics</h2>
<p>The ingenuity of Starship is that it just “belly-flops” all the way down – a type of free fall in which the atmosphere gradually slows down its speed. As it nears the ground, it should be slow enough for a short flip-and-landing burn to touch down softly on the pad. </p>
<figure class="align-center ">
<img alt="Picture of a man belly flopping into water." src="https://images.theconversation.com/files/374765/original/file-20201214-20-1gfo9ke.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/374765/original/file-20201214-20-1gfo9ke.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=388&fit=crop&dpr=1 600w, https://images.theconversation.com/files/374765/original/file-20201214-20-1gfo9ke.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=388&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/374765/original/file-20201214-20-1gfo9ke.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=388&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/374765/original/file-20201214-20-1gfo9ke.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=488&fit=crop&dpr=1 754w, https://images.theconversation.com/files/374765/original/file-20201214-20-1gfo9ke.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=488&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/374765/original/file-20201214-20-1gfo9ke.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=488&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">Engineering inspiration: the epic belly flop.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/boy-belly-flops-into-spring-1384125">Stacey Lynn Payne/Shuttestock</a></span>
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<p>No other vehicle flies like this on purpose. Planes are designed to keep the air flow attached to the wings to provide lift. If you lose that air flow, you fall out of the sky – a condition called stall. Starship enters the atmosphere at a 90 degree angle. That means it is fully stalled. Just as a leaf flutters to the ground this is an inherently unstable configuration and the aerodynamics are impossible to predict.</p>
<p>This is where active control comes in. Starship has four flaps and they’re used just as a skydiver uses their four arms to control free fall. With the SN8 test flight, Space X has shown that it’s possible to control a belly-flop. The drop from 12.5km gave SpaceX the conditions of the last half of a return back from orbit. </p>
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<p>SpaceX will have gathered flight data that allows it to know how the aerodynamics of a belly-flop work. In particular, it will know how well the flaps work and how precisely to keep the craft stable and land it on target. We can see on the videos released by SpaceX that the flaps are under good control. This looks like great news for SpaceX.</p>
<h2>Rocket equation</h2>
<p>Being fully reusable, Starship should work out far cheaper than conventional single use craft. But it’s a tricky business to work out exactly how much fuel you need to carry. Conventional aircraft always take off with a bit of fuel to spare, but they can always make an emergency landing if they miscalculate.</p>
<p>Rockets need to launch with an enormous amount of fuel just to be sure you have enough for the landing. It’s like going on a 14-day camping trip and spending 13 days carrying the water for your last day. It’s likely that the tank for SN8 was almost completely empty when it came in to land. </p>
<p>The amount of fuel you need is given by “<a href="https://www.grc.nasa.gov/www/k-12/rocket/rktpow.html">the rocket equation</a>”. This shows that if you want to launch 100 tonnes of payload to the Moon at a speed of 12,000 metres per second you need a staggering 2,000 tonnes of fuel. </p>
<p>When it comes to the type of fuel, it’s interesting that kerosene and hydrogen (as used by Apollo 11) are still the most popular rocket fuels around. The laws of physics and chemistry haven’t changed very much in fifty years. But Starship is actually pioneering the use of methane as a fuel. Despite being harder to work with, it gives a bit more thrust. And perhaps more importantly <a href="https://www.nasa.gov/feature/jpl/curiosity-detects-unusually-high-methane-levels">there’s plenty of methane on Mars</a>, which is obviously the ultimate destination for SpaceX. </p>
<p>So why did SN8 crash? You can see in the video some green flashes just before landing. The engines are made with copper, which burns with a characteristic green flame. SpaceX says there was a problem with <a href="https://twitter.com/elonmusk/status/1336809767574982658">fuel pressure</a> just at the last moment, meaning the rocket couldn’t slow down. The resulting excess oxygen started burning up the engines themselves. If it weren’t for the last few seconds then the landing could have been perfect. Engineers will now be looking to fix that problem for SN9.</p><img src="https://counter.theconversation.com/content/152022/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Hugh Hunt is affiliated with the University of Cambridge</span></em></p>Starship’s groundbreaking design will help it land safely on Mars one day.Hugh Hunt, Reader in Engineering Dynamics and Vibration, University of CambridgeLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1219022019-09-19T11:28:04Z2019-09-19T11:28:04ZSail GP: how do supercharged racing yachts go so fast? An engineer explains<p>Sailing used to be considered as a rather sedate pastime. But in the past few years, the world of yacht racing has been revolutionised by the arrival of hydrofoil-supported catamarans, known as “foilers”. These vessels, more akin to high-performance aircraft than yachts, combine the laws of aerodynamics and hydrodynamics to create vessels capable of speeds of up to 50 knots, which is far faster than the wind propelling them.</p>
<p>An <a href="https://sailgp.com/about/f50-catamaran/">F50 catamaran</a> preparing for the Sail GP series recently even broke this barrier, <a href="https://www.sail-world.com/news/220675/5022-knots-for-GBR-SailGP-team">reaching an incredible speed of 50.22 knots</a> (57.8mph) purely powered by the wind. This was achieved in a wind of just 19.3 knots (22.2mph). F50s are 15-metre-long, 8.8-metre-wide hydrofoil catamarans propelled by rigid sails and capable of such astounding speeds that Sail GP has been called the “<a href="http://www.sportspromedia.com/interviews/sailgp-americas-cup-russell-coutts-interview">Formula One of sailing</a>”. How are these yachts able to go so fast? The answer lies in some simple fluid dynamics.</p>
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<p>As a vessel’s hull moves through the water, there are two primary physical mechanisms that create drag and slow the vessel down. To build a faster boat you have to find ways to overcome the drag force.</p>
<p>The first mechanism is friction. As the water flows past the hull, a microscopic layer of water is effectively attached to the hull and is pulled along with the yacht. A second layer of water then attaches to the first layer, and the sliding or shearing between them creates friction. </p>
<p>On the outside of this is a third layer, which slides over the inner layers creating more friction, and so on. Together, these layers are known as the <a href="http://web.mit.edu/fluids-modules/www/highspeed_flows/ver2/bl_Chap2.pdf">boundary layer</a> – and it’s the shearing of the boundary layer’s molecules against each other that creates frictional drag.</p>
<p>A yacht also makes waves as it pushes the water around and under the hull from the bow (front) to the stern (back) of the boat. The waves form two distinctive patterns around the yacht (one at each end), known as <a href="https://www.math.ubc.ca/%7Ecass/courses/m309-01a/carmen/Mainpage.htm">Kelvin Wave</a> patterns. </p>
<p>These waves, which move at the same speed as the yacht, are very energetic. This creates drag on the boat known as the wave-making drag, which is responsible for around 90% of the total drag. As the yacht accelerates to faster speeds (close to the “hull speed”, explained later), these waves get higher and longer.</p>
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<p>These two effects combine to produce a phenomenon known as “<a href="https://iopscience.iop.org/article/10.1088/1361-6404/aab982/pdf">hull speed</a>”, which is the fastest the boat can travel – and in conventional single-hull yachts it is very slow. A single-hull yacht of the same size as the F50 has a hull speed of around 12 mph.</p>
<h2>Hydrofoils</h2>
<p>However, it’s possible to reduce both the frictional and wave-making drag and overcome this hull-speed limit by building a yacht with <a href="https://www.sciencedirect.com/topics/engineering/hydrofoil-craft">hydrofoils</a>. Hydrofoils are small, underwater wings. These act in the same way as an aircraft wing, creating a lift force which acts against gravity, lifting our yacht upwards so that the hull is clear of the water.</p>
<p>While an aircraft’s wings are very large, the <a href="https://www.grc.nasa.gov/www/k-12/airplane/density.html">high density of water compared to air</a> means that we only need very small hydrofoils to produce a lot of the important lift force. A hydrofoil just the size of three A3 sheets of paper, when moving at just 10 mph, can produce enough lift to pick up a large person.</p>
<p>This significantly reduces the surface area and the volume of the boat that is underwater, which cuts the frictional drag and the wave-making drag, respectively. The combined effect is a reduction in the overall drag to a fraction of its original amount, so that the yacht is capable of sailing much faster than it could without hydrofoils.</p>
<p>The other innovation that helps boost the speed of racing yachts is the use of <a href="https://www.scientificamerican.com/article/americas-cup-fixed-wing-sail/">rigid sails</a>. The power available from traditional sails to drive the boat forward is relatively small, limited by the fact that the sail’s forces have to act in equilibrium with a range of other forces, and that fabric sails do not make an ideal shape for creating power. Rigid sails, which are very similar in design to an aircraft wing, form a much more efficient shape than traditional sails, effectively giving the yacht a larger engine and more power. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/qUsqztcOI7I?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>As the yacht accelerates from the driving force of these sails, it experiences what is known as “<a href="http://sailingmagazine.net/article-permalink-914.html">apparent wind</a>”. Imagine a completely calm day, with no wind. As you walk, you experience a breeze in your face at the same speed that you are walking. If there was a wind blowing too, you would feel a mixture of the real (or “true” wind) and the breeze you have generated.</p>
<p>The two together form the apparent wind, which can be faster than the true wind. If there is enough true wind combined with this apparent wind, then significant force and power can be generated from the sail to propel the yacht, so it can easily sail faster than the wind speed itself. </p>
<p>The combined effect of reducing the drag and increasing the driving power results in a yacht that is far faster than those of even a few years ago. But all of this would not be possible without one further advance: materials. In order to be able to “fly”, the yacht must have a low mass, and the hydrofoil itself must be very strong. To achieve the required mass, strength and rigidity using traditional boat-building materials such as wood or aluminium would be very difficult.</p>
<p>This is where modern advanced composite materials such as <a href="https://www.yachtsinternational.com/owners-lounge/carbon-fiber-the-new-black">carbon fibre</a> come in. Production techniques optimising weight, rigidity and strength allow the production of structures that are strong and light enough to produce incredible yachts like the F50.</p>
<p>The engineers who design these high-performance boats (known as <a href="https://www.rina.org.uk/careers_in_naval_architecture.html">naval architects</a>) are always looking to use new materials and science to get an optimum design. In theory, the F50 should be able to go even faster.</p><img src="https://counter.theconversation.com/content/121902/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jonathan Ridley does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>F50 catamarans used in the “Formula One"of sailing can travel at up to 50 knots.Jonathan Ridley, Head of Engineering, Warsash School of Maritime Science and Engineering, Solent UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1223212019-08-28T20:01:47Z2019-08-28T20:01:47ZHow fast can a human cycle? With aerodynamic help, the 300km per hour barrier seems easily within reach<figure><img src="https://images.theconversation.com/files/289793/original/file-20190828-184234-1xoqopx.png?ixlib=rb-1.1.0&rect=3%2C0%2C829%2C435&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">With aerodynamics out of the equation, it's possible to go really, really fast.</span> <span class="attribution"><span class="source">YouTube/Euronews</span></span></figcaption></figure><p>British cyclist Neil Campbell <a href="https://www.bbc.com/news/uk-england-essex-49393888">recently set a new record</a> for the men’s “fastest bicycle in a slipstream”, clocking up a breathtaking 280km per hour. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/AMtFpDQ4RzA?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Neil Campbell’s record-breaking performance.</span></figcaption>
</figure>
<p>This record involves bringing a cyclist up to speed in the wake of a towing vehicle, then releasing the bike and timing the rider over a 200m distance. The overall record stands at 296km per hour, <a href="https://www.guinnessworldrecords.com/world-records/426619-fastest-bicycle-speed-in-slipstream-female">set in September 2018 by Denise Mueller-Korenek</a>, who was towed by a dragster on Utah’s Bonneville Salt Flats.</p>
<p>But just how much can these high cycling speeds can be attributed to human performance? Does it take a supreme athlete to maintain that speed after release, or is the vehicle really doing all the hard work? And if so, does that mean even faster records are possible? </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/yes-there-is-a-limit-to-athletic-ability-physics-8343">Yes, there is a limit to athletic ability – physics</a>
</strong>
</em>
</p>
<hr>
<p>By considering the energy supply and demand involved in Campbell’s new men’s record, we can begin to appreciate the relative contributions from human and machine. For this record, energy comes from both the car’s fuel combustion and from human power. </p>
<p>The power required to maintain a given speed depends on the resistive force acting against the rider’s forward motion. On a flat course at a constant speed, there are two key components:</p>
<ul>
<li><strong>aerodynamic resistance</strong>, also known as aerodynamic drag </li>
<li><strong>rolling resistance</strong>, which broadly covers the friction between wheels and road, the friction in the wheel bearings, and the efficiency of power transmission from the pedals through the chain to the wheels. </li>
</ul>
<p>Crucially, aerodynamic resistance <a href="https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/drag-kings-characterizing-largescale-flows-in-cycling-aerodynamics/1E4A39549041D3A8F9C9033BC269C5D0">increases with the square of air speed</a>, which means it increases very rapidly as the speed increases. Rolling resistance, meanwhile, increases linearly with speed, which means it increases much less rapidly as speed rises.</p>
<p>Benjamin Thiele, lead systems engineer of the Monash Human Power Team at Monash University, explains it like this:</p>
<blockquote>
<p>Basically, if you want to cycle fast and you had the option to exclude one of the resistive forces from the physics, you would be wise to remove the aerodynamic component. </p>
</blockquote>
<p>To put this in context, in elite level track cycling (where there are obviously no cars to hide behind!), aerodynamic drag typically accounts for <a href="https://journals.humankinetics.com/view/journals/jab/14/3/article-p276.xml">about 95% of the total resistive force</a>.</p>
<p>Thus the towing vehicle in Campbell’s record attempt helped him in two crucial ways. First, it brought him up to speed, thus reducing his energy expenditure during acceleration. </p>
<p>Second, the car’s slipstream attachment (basically a cross between a spoiler and a tent, behind which Campbell positioned himself during the ride) removed much of the aerodynamic resistance that would otherwise become insurmountable at such dizzying speeds.</p>
<p>By riding in the vehicle’s wake, the rider will experience both low relative wind speeds and low aerodynamic resistance. In fact, if the rider is positioned correctly, the air flow in the car’s wake can actually generate a <a href="https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930091542.pdf">propulsive aerodynamic force</a> – effectively, the vehicle “drags” some air behind it, and the rider can thus be sucked along with it.</p>
<p>What about the physical demands of maintaining that speed after the tow release? This primarily depends on the size of the gear being used, and of the rolling resistance that needs to be overcome. By my calculations, and assuming aerodynamic drag behind the tow car is negligible, hitting 300km per hour (the next big milestone for both the mens’ and womens’ slipstream records) would require the rider to maintain a power output of 600-700 watts for the 2.4 seconds it would take to ride through the 200m time trap.</p>
<p>This seems achievable enough, given Tour de France riders can put out more than 1,000W for a <a href="https://www.cyclingweekly.com/news/racing/data-reveals-the-most-powerful-sprints-of-2018-and-the-numbers-are-pretty-mind-blowing-359140">full minute or more</a>.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/the-aerodynamics-of-a-tour-de-france-time-trial-29568">The aerodynamics of a Tour de France time trial</a>
</strong>
</em>
</p>
<hr>
<p>So the tow vehicle is really the crucial factor, rather than the rider’s physical performance. In fact, if the rider were to pull out of the slipstream after being towed up to 300km per hour, the energy demand to maintain this speed would be on the order of 100 kilowatts – roughly the performance of a high-powered motorcycle!</p>
<h2>What about unassisted cycling records?</h2>
<p>Given the crucial importance of overcoming aerodynamic drag, it’s no surprise elite cycling teams invest so much into <a href="https://link.springer.com/article/10.1007/s12283-017-0234-1">aerodynamics research and development</a>.</p>
<p>In fact, the aerodynamics of conventional bicycles and riding positions are far from optimal. This is evident when we compare speeds achieved on conventional bicycles with those of a “faired recumbent human-powered vehicle”. This is a modified bicycle on which the rider lies down in a recumbent position, with the pedals at the front, inside an aerodynamic covering called a fairing.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/289736/original/file-20190828-184229-kma0y6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/289736/original/file-20190828-184229-kma0y6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/289736/original/file-20190828-184229-kma0y6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/289736/original/file-20190828-184229-kma0y6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/289736/original/file-20190828-184229-kma0y6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/289736/original/file-20190828-184229-kma0y6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=753&fit=crop&dpr=1 754w, https://images.theconversation.com/files/289736/original/file-20190828-184229-kma0y6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=753&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/289736/original/file-20190828-184229-kma0y6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=753&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A faired recumbent bicycle designed, developed and manufactured by Monash University students.</span>
</figcaption>
</figure>
<p>The speed record for such a vehicle over a 200m distance currently stands at <a href="https://www.popularmechanics.com/technology/a22946/human-powered-speed-record-aerovelo/">144km per hour</a>. This is about twice as fast as peak speeds achieved during velodrome sprints on a conventional track bicycle. </p>
<p>David Burton, manager of Monash University’s <a href="https://www.monash.edu/research/infrastructure/platforms-pages/wind-tunnel">wind tunnel research facility</a>, says elite cycling has “already exhausted the low-hanging fruit when it comes to gaining a competitive advantage through aerodynamics”, given the rules and constraints of the sport in terms of equipment design and rider position. </p>
<p>But he adds there are still some high-tech research avenues to improving performance, including “advanced experimental testing techniques and highly resolved numerical simulations of the flow fields around cyclists”.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/289738/original/file-20190828-184234-1xopel6.PNG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/289738/original/file-20190828-184234-1xopel6.PNG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/289738/original/file-20190828-184234-1xopel6.PNG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=231&fit=crop&dpr=1 600w, https://images.theconversation.com/files/289738/original/file-20190828-184234-1xopel6.PNG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=231&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/289738/original/file-20190828-184234-1xopel6.PNG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=231&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/289738/original/file-20190828-184234-1xopel6.PNG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=290&fit=crop&dpr=1 754w, https://images.theconversation.com/files/289738/original/file-20190828-184234-1xopel6.PNG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=290&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/289738/original/file-20190828-184234-1xopel6.PNG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=290&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Experimental and numerical techniques being employed by researchers at Monash University, The Australian Institute of Sport and Cycling Australia to optimise elite level cycling performance.</span>
</figcaption>
</figure>
<p>As we have seen above, there is probably still the potential for even greater speeds when it comes to slipstream-assisted cycling. I suggest it’s within the realm of current elite-level human performance to achieve speeds approaching 400km per hour when enveloped in the wake of a vehicle.</p>
<p>Perhaps the challenge ultimately then becomes a psychological one: would anyone dare attempt it?</p><img src="https://counter.theconversation.com/content/122321/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Timothy Crouch does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>British cyclist Neil Campbell has set a new men’s speed record for slipstreaming behind a car. But his speed of 280km an hour, while breathtaking, has not taken human cycling performance to the limit.Timothy Crouch, Experimental Aerodynamicist, Monash UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1143942019-04-08T10:42:55Z2019-04-08T10:42:55ZToo many airplane systems rely on too few sensors<figure><img src="https://images.theconversation.com/files/267199/original/file-20190402-177175-6046gt.jpg?ixlib=rb-1.1.0&rect=291%2C0%2C4700%2C1661&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Planes have many sensors, supplying all kinds of useful data.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/business-jet-airplane-gear-down-landing-1310559680?src=unD8nxhH5kTmylCMzugfLg-1-92">vaalaa/Shutterstock.com</a></span></figcaption></figure><p>The <a href="https://www.nytimes.com/2019/03/25/business/boeing-simulation-error.html">apparent connection</a> between fatal airplane <a href="https://www.nytimes.com/interactive/2019/03/13/world/boeing-737-crash-investigation.html">crashes in Indonesia and Ethiopia</a> centers around the <a href="https://www.washingtonpost.com/business/economy/sensor-cited-as-potential-factor-in-boeing-crashes-draws-scrutiny/2019/03/17/5ecf0b0e-4682-11e9-aaf8-4512a6fe3439_story.html">failure of a single sensor</a>. I know what that’s like: A few years ago, while I was flying a Cessna 182-RG from Albany, New York, to Fort Meade, Maryland, my airspeed indicator showed that I was flying at a speed so slow that my plane was at risk of no longer generating enough lift to stay in the air.</p>
<p>Had I trusted my airspeed sensor, I would have pushed the plane’s nose down in an attempt to regain speed, and possibly put too much strain on the aircraft’s frame, or gotten dangerously close to the ground. But even small aircraft are packed with sensors: While worried about my airspeed, I noticed that my plane was staying at the same altitude, the engine was generating the same amount of power, the wings were meeting the air at a constant angle and I was still moving over the ground at the same speed I had been before the airspeed allegedly dropped.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/267200/original/file-20190402-177175-m0aof4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/267200/original/file-20190402-177175-m0aof4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/267200/original/file-20190402-177175-m0aof4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=329&fit=crop&dpr=1 600w, https://images.theconversation.com/files/267200/original/file-20190402-177175-m0aof4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=329&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/267200/original/file-20190402-177175-m0aof4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=329&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/267200/original/file-20190402-177175-m0aof4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=413&fit=crop&dpr=1 754w, https://images.theconversation.com/files/267200/original/file-20190402-177175-m0aof4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=413&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/267200/original/file-20190402-177175-m0aof4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=413&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A Cessna 182 in flight.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/131806380@N05/17246847205">Rob Hodgkins/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>So instead of overstressing and potentially crashing my plane, I was able to fix the problematic sensor and continue my flight without further incident. As a result, I started investigating how <a href="https://doi.org/10.1109/MAES.2017.150242">computers can use data from different aircraft sensors</a> to help pilots understand whether there’s a real emergency happening, or something much less severe.</p>
<p>Boeing’s response to its crashes has included designing a software update that will <a href="https://www.nytimes.com/2019/03/25/business/boeing-simulation-error.html">rely on two sensors instead of one</a>. That may not be enough. </p>
<h2>Cross-checking sensor data</h2>
<p>As a plane defies gravity, aerodynamic principles expressed as mathematical formulas govern its flight. Most of an aircraft’s sensors are intended to monitor elements of those formulas, to reassure pilots that everything is as it should be – or to alert them that something has gone wrong.</p>
<p>My team developed <a href="http://wcl.cs.rpi.edu/pilots/">a computer system</a> that looks at information from many sensors, comparing their readings to each other and to the relevant mathematical formulas. This system can detect inconsistent data, indicate which sensors most likely failed and, in certain circumstances, use other data to estimate the correct values that these sensors should be delivering.</p>
<p>For instance, my Cessna encountered problems when the primary airspeed sensor, called a “<a href="https://www.scientificamerican.com/article/what-is-a-pitot-tube/">pitot tube</a>,” froze in cold air. Other sensors on board gather related information: GPS receivers measure how quickly the aircraft is covering ground. Wind speed data is available from computer models that forecast weather prior to the flight. Onboard computers can calculate an estimated airspeed by combining GPS data with information on the wind speed and direction.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/266148/original/file-20190327-139341-ufpu9u.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/266148/original/file-20190327-139341-ufpu9u.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/266148/original/file-20190327-139341-ufpu9u.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=313&fit=crop&dpr=1 600w, https://images.theconversation.com/files/266148/original/file-20190327-139341-ufpu9u.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=313&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/266148/original/file-20190327-139341-ufpu9u.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=313&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/266148/original/file-20190327-139341-ufpu9u.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=393&fit=crop&dpr=1 754w, https://images.theconversation.com/files/266148/original/file-20190327-139341-ufpu9u.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=393&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/266148/original/file-20190327-139341-ufpu9u.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=393&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Using information on ground speed and the current wind conditions, a computer can estimate the plane’s airspeed.</span>
<span class="attribution"><span class="source">Shigeru Imai and Carlos Varela</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>If the computer’s estimated airspeed agrees with the sensor readings, most likely everything is fine. If they disagree, then something is wrong – but what? It turns out that <a href="https://doi.org/10.1109/MAES.2017.150242">these calculations disagree in different ways</a>, depending on which one – or more – of the GPS, wind data or airspeed sensors is wrong.</p>
<h2>A test with real data</h2>
<p>We tested our computer program with real data from the 2009 crash of Air France Flight 447. The post-crash investigation revealed that <a href="https://www.npr.org/sections/thetwo-way/2012/07/05/156303873/crash-report-confirm-air-france-447-crashed-due-to-faulty-sensors-pilot-error">three different pitot tubes</a> froze up, <a href="http://www.spiegel.de/international/world/death-in-the-atlantic-the-last-four-minutes-of-air-france-flight-447-a-679980.html">delivering an erroneous airspeed reading</a> and triggering a chain of events ending in the plane plunging into the Atlantic Ocean, killing 228 passengers and crew.</p>
<p>The flight data showed that when the pitot tubes froze, they suddenly stopped registering airspeed as 480 knots, and instead reported the plane was going through the air at 180 knots – so slow the autopilot turned itself off and alerted the human pilots there was a problem.</p>
<p>But the onboard GPS recorded that the plane was traveling across the ground at 490 knots. And computer models of weather indicated the wind was coming from the rear of the plane at about 10 knots.</p>
<p>When we fed those data to our computer system, it <a href="https://doi.org/10.1109/MAES.2017.150242">detected that the pitot tubes had failed</a>, and estimated the plane’s real airspeed within five seconds. It also detected when the pitot tubes thawed again, about 40 seconds after they froze, and was able to confirm that their readings were again reliable.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/7G9FLFIdnx8?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">When one sensor fails, other equipment can provide data to detect the failure and even estimate values for the failing sensor.</span></figcaption>
</figure>
<h2>A different sort of test</h2>
<p>We also used our system to identify what happened to <a href="https://en.wikipedia.org/wiki/Tuninter_Flight_1153">Tuninter Flight 1153</a>, which ditched into the Mediterranean Sea in 2005 on its way from Italy to Tunisia, killing 16 of the 39 people aboard.</p>
<p>After the accident, the investigation revealed that maintenance workers had mistakenly <a href="https://www.flightglobal.com/news/articles/tuninter-atr-72-had-been-fitted-with-wrong-fuel-gaug-201462/">installed the wrong fuel quantity indicator</a> on the plane, so it reported 2,700 kg of fuel was in the tanks, when the plane was really carrying only 550 kg. Human pilots didn’t notice the error, and the plane ran out of fuel.</p>
<p>Fuel is heavy, though, and its weight affects the performance of an aircraft. A plane with too little fuel would have handled differently than one with the right amount. To calculate whether the plane was behaving as it should, with the right amount of fuel on board, we used the <a href="https://doi.org/10.1007/s10586-017-1291-8">aerodynamic mathematical relationship between airspeed and lift</a>. When a plane is in level flight, lift equals weight. Everything else being the same, a <a href="https://doi.org/10.1109/MAES.2017.150242">heavier plane should have been going slower</a> than the Tuninter plane was. </p>
<p>Our program models only cruise phases of flight, in which the plane is in steady, level flight – not accelerating or changing altitude. But it would have been sufficient to detect that the plane was too light and alert the pilots, who could have turned around or landed elsewhere to refuel. Adding information about other phases of flight could improve the system’s accuracy and responsiveness.</p>
<h2>What about the Boeing 737 Max 8 crashes?</h2>
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<a href="https://images.theconversation.com/files/266135/original/file-20190327-139371-1x1l6r9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/266135/original/file-20190327-139371-1x1l6r9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/266135/original/file-20190327-139371-1x1l6r9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=185&fit=crop&dpr=1 600w, https://images.theconversation.com/files/266135/original/file-20190327-139371-1x1l6r9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=185&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/266135/original/file-20190327-139371-1x1l6r9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=185&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/266135/original/file-20190327-139371-1x1l6r9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=232&fit=crop&dpr=1 754w, https://images.theconversation.com/files/266135/original/file-20190327-139371-1x1l6r9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=232&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/266135/original/file-20190327-139371-1x1l6r9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=232&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">The angle of attack describes how the wings meet the oncoming air.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Airfoil_angle_of_attack.jpg">J Doug McLean/Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
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</figure>
<p>The full range of data about Lion Air 610 and Ethiopian Airlines 302 is not yet available to the public, but early reports suggest there was a <a href="https://www.nytimes.com/2019/04/04/world/asia/ethiopia-crash-boeing.html">problem with one of the angle-of-attack sensors</a>. My research team developed a method to check that device’s accuracy based on the plane’s airspeed.</p>
<p>We used aerodynamics and a flight simulator to measure how variations in the angle of attack – the steepness with which the wings meet the oncoming air – changed the horizontal and vertical speed of a Cessna 172. The data were consistent with the performance of an actual Cessna 172 in flight. Using our model and system, we can distinguish between an actual emergency – a dangerously high angle of attack – and a failing sensor providing erroneous data.</p>
<p><iframe id="J35Sz" class="tc-infographic-datawrapper" src="https://datawrapper.dwcdn.net/J35Sz/2/" height="400px" width="100%" style="border: none" frameborder="0"></iframe></p>
<p>The actual numbers for a Boeing 737 Max 8 would be different, of course, but the principle is still the same, using the mathematical relationship between angle of attack and airspeed to double-check each other, and to identify faulty sensors.</p>
<h2>Better still</h2>
<p>As my team continues to develop flight data analysis software, we’re also working on supplying it with better data. One potential source could be <a href="https://www.nsf.gov/awardsearch/showAward?AWD_ID=1816307&HistoricalAwards=false">letting airplanes communicate directly with each other</a> about weather and wind conditions in specific locations at particular altitudes. We are also working <a href="https://news.rpi.edu/approach/2019/01/31/grant-awarded-to-increase-intelligence-in-aerospace-systems/">on methods to precisely describe safe operating conditions</a> for flight software that relies on sensor data.</p>
<p>Sensors do fail, but even when that happens, automated systems can be <a href="https://theconversation.com/your-next-pilot-could-be-drone-software-92330">safer and more efficient than human pilots</a>. As flight becomes <a href="https://theconversation.com/despite-consumer-worries-the-future-of-aviation-will-be-more-automated-113807">more automated and increasingly reliant on sensors</a>, it is imperative that flight systems cross-check data from different sensor types, to safeguard against otherwise potentially fatal sensor faults.</p><img src="https://counter.theconversation.com/content/114394/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Carlos Varela currently receives funding from the Air Force Office of Scientific Research (DDDAS Grant No. FA9550-19-1-0054) and the National Science Foundation (CISE Grant No. CNS-1816307).</span></em></p>A pilot and researcher knows that airplanes are full of sensors – and finds a way onboard computers can use the data to detect equipment failure and tell pilots what’s a real emergency and what’s not.Carlos Varela, Associate Professor of Computer Science, Rensselaer Polytechnic InstituteLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1065392018-11-19T19:02:05Z2018-11-19T19:02:05ZYour riding position can give you an advantage in a road cycling sprint<p>Many professional road cycling events are hundreds of kilometres long, but the final placings are often decided by what happens in the last few seconds of any race stage.</p>
<p><a href="https://doi.org/10.1123/ijspp.2018-0560">New research</a> shows that a rider can gain up to an extra 5kph advantage in those final sprint seconds, and it all depends on how they position themselves on their bicycle.</p>
<p>That can be enough to make the difference between winning or losing a race.</p>
<h2>Race to the finish</h2>
<p>If you’ve ever watched a professional road cycling event, either live or on television, you know they can go on for several days or even weeks.</p>
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<p>But more than half of the stages during the Santos Tour Down Under and the Tour de France, as well as some of the recent World Championships, were won in either a head-to-head, small group, or mass sprint finish.</p>
<p>The average speed during professional road cycling sprints is 63.9kph (53.7-69.1kph) sustained for between 9 and 17 seconds for <a href="https://doi.org/10.1055/s-0035-1554697">men</a>, and 53.8kph (41.6-64kph) for 10-30 seconds for <a href="https://doi.org/10.1123/ijspp.2017-0757">women</a>.</p>
<p>During the sprint, men produce peak power outputs between 13.9 and 20.0 Watts per kilogram (989-1,443 Watts), and women 10.8-16.2 Watts per kilogram (716-1,088 Watts).</p>
<p>But peak power output is not the only important factor to win the sprint, with <a href="https://www.ncbi.nlm.nih.gov/pubmed/23038704">tactics</a> playing a significant role.</p>
<p>Our new research, <a href="https://doi.org/10.1123/ijspp.2018-0560">published this month in the International Journal of Sports Physiology and Performance</a>, shows that adopting a forward standing position during a sprint could give riders a speed boost of up to 5kph.</p>
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<a href="https://images.theconversation.com/files/245432/original/file-20181113-194491-opqwqp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/245432/original/file-20181113-194491-opqwqp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/245432/original/file-20181113-194491-opqwqp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=236&fit=crop&dpr=1 600w, https://images.theconversation.com/files/245432/original/file-20181113-194491-opqwqp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=236&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/245432/original/file-20181113-194491-opqwqp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=236&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/245432/original/file-20181113-194491-opqwqp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=297&fit=crop&dpr=1 754w, https://images.theconversation.com/files/245432/original/file-20181113-194491-opqwqp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=297&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/245432/original/file-20181113-194491-opqwqp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=297&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">The three tested sprinting positions from left to right: seated, standing, and forward standing.</span>
<span class="attribution"><span class="source">International Journal of Sports Physiology and Performance</span>, <span class="license">Author provided</span></span>
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<h2>The drag on a cyclist</h2>
<p>Cycling speed is affected by several factors, including power output, aerodynamic drag (CdA), road characteristics, and environmental variables. </p>
<p>During the sprint, roughly 95% of the total resistive forces working against the rider is caused by aerodynamic resistance. Therefore, it is important to reduce aerodynamic drag in road cycling, particularly during the sprint which is the fastest activity on the bicycle (with the exclusion of some downhill riding during a race).</p>
<p>Given that the outcomes of road cycling sprints are often decided by very small margins – in one race stage down to <a href="https://www.eurosport.com/cycling/tour-de-france/2017/tour-de-france-2017-stage-7-analysis-boasson-hagen-denied-win-by-just-0.0003-seconds_sto6245740/story.shtml">just 0.0003 seconds</a> – the aerodynamics are meaningful to overall sprint performances.</p>
<p>Studies on flow dynamics in cycling have shown that <a href="https://journals.sagepub.com/doi/abs/10.1177/1754337114549876">lowering the head and torso</a> significantly reduces wind resistance. </p>
<p>That is why several cyclists have, over the past few years, begun to adopt a forward standing cycling sprint position. </p>
<p>This novel sprint position has already shown to be successful at the highest level of professional cycling, in events such as the Giro d’Italia and Vuelta a España and in Australia’s biggest road cycling race, the Santos Tour Down Under (see video, below). </p>
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<figcaption><span class="caption">Santos Tour Down Under 2016 stage 6 victory in the forward standing position.</span></figcaption>
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<h2>Body position to the test</h2>
<p>To better understand why this forward standing position may give riders an advantage, we compared it with the more traditional seated and standing sprint positions. </p>
<p>During the study, participants rode 250 metres in two directions at 25kph, 32kph and 40kph and in each of the three positions, resulting in a total of 18 efforts per participant.</p>
<p>During these efforts we measured cycling velocity, power output, road gradient, wind velocity and direction, temperature, humidity, and barometric pressure. </p>
<p>We then used these variables, together with the weight of the cyclist and bicycle, and constants for rolling resistance and the efficiency of the drive system, in a mathematical model to calculate the aerodynamic drag.</p>
<p>This model has <a href="https://doi.org/10.1249/01.mss.0000193560.34022.04">previously</a> been shown to give valid measurements compared with a wind tunnel.</p>
<h2>The results are in</h2>
<p>We found the forward standing cycling sprint position resulted in a 23-26% reduction in aerodynamic drag compared with a seated and standing position, respectively. </p>
<p>This decrease in drag could potentially result in an important increase in cycling sprint velocity of 3.9-4.9kph.</p>
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<p>Throughout the average duration of a typical road cycling sprint (about 14 seconds) this would result in a gain of 15-19 metres, which is why it could mean the difference between winning and losing a race. </p>
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<figcaption><span class="caption">How ECU is helping the world’s best cyclists improving their sprint performance.</span></figcaption>
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<p>While this novel position was more aerodynamic, it is plausible that changes in body position may influence a rider’s movement kinetics, and therefore increasing or decreasing power output. This is currently under investigation in this PhD project.</p>
<p>But cyclists who want to improve their sprint performance might want to start practising the forward standing position. It takes time to learn how to sprint in that position but you could gain those aerodynamic benefits, and potentially win more races.</p><img src="https://counter.theconversation.com/content/106539/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Paul Franciscus Johannes Merkes receives funding from Orica-GreenEDGE and ECU (scholarship). </span></em></p><p class="fine-print"><em><span>Chris Abbiss has received funding from from New Global Cycling Services and Cycling Australia for research outlined in this article. </span></em></p>Most long distance road cycling events are won or lost in the final sprint of any race stage. Here’s one tip that could give you an extra 5kph advantage.Paul Franciscus Johannes Merkes, PhD candidate, Edith Cowan UniversityChris Abbiss, Associate professor, Edith Cowan UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/919362018-02-19T13:40:58Z2018-02-19T13:40:58ZWere Team GB’s skeleton suits responsible for fantastic three medal haul?<p>Team GB skeleton rider Lizzie Yarnold won a <a href="http://www.bbc.co.uk/sport/winter-olympics/42981272">stunning Winter Olympic gold</a> on February 17, backed up by bronzes for Laura Deas and Dom Parsons. Thanks to drag-resistant ridges, 3D laser scanning and topnotch material, Team GB’s skeleton suits are <a href="https://www.theguardian.com/sport/2018/feb/12/gb-skeleton-pyeongchang-skin-suits-british-cycling">said to</a> have provided up to a one-second advantage per run over the rest of the field and have been a hot topic of <a href="https://www.usatoday.com/story/sports/winter-olympics-2018/2018/02/15/2018-winter-olympics-british-skeleton-suits-create-controversy/339893002/">controversy</a>. </p>
<p>What makes these revolutionary suits so speedy – and just how important were these technological innovations in Team GB’s riders’ success? The Conversation put these questions to Nick Martin, senior lecturer in Aerodynamics at Northumbria University.</p>
<p><strong>How do the suits give the riders their extra speed?</strong></p>
<p>The aerodynamics of a skeleton bobsled and rider are complex, and our knowledge of fluid mechanics is far from complete. This creates opportunities for research and development programmes that push the frontiers of our aerodynamic understanding to produce technological innovations that give riders an all-important edge.</p>
<p>Drag is the aerodynamic force that opposes an object’s motion through air and slows it down. Only about 10% of the drag force acting on skeleton riders comes from the bobsled, meaning that the greatest potential for improving the time it takes to traverse the 1,376.38 meter track in Pyeongchang is to optimising the aerodynamics of the athletes themselves.</p>
<p>The drag acting on the riders comes from two sources. Air moving close to the athletes’ bodies moves slower than air further away, causing friction along the athletes’ skin suits. In addition, as athletes move down the track, air directly in front of them becomes more compressed and air behind them becomes less dense. This pressure difference acts to both “push” against the athletes from the front and “pull” them back at the same time, slowing them down.</p>
<p>Pressure drag accounts for more than 90% of the overall drag on both the rider and bobsled. The amount of pressure drag is influenced by the shape of the athlete, so aerodynamics experts can most effectively attempt to make performance gains by refining the athletes’ helmets and suits.</p>
<p>Skeleton suits are made out of an elastic material called polyurethane. All teams use this material, but the addition of drag-resistant ridges and the use of 3D scanning allows the suit designers to make subtle changes to the athletes’ shape that seems to set apart Team GB’s suits. This fine tuning is comparable to the careful design engineering of Formula One cars and aeroplanes to perfect their aerodynamic behaviour.</p>
<p>The drag-resistant ridges on Team GB’s suits introduce turbulence into the thin layer of air surrounding the athlete, known as the boundary layer. A turbulent boundary layer actually causes more skin friction, but is less likely to separate when it encounters a seam in the skin suit, a folded ridge of material, or a curved surface. Separation creates pockets of low-pressure, slow-moving air, too much of which can cause large increases in pressure drag. The ridges minimise pressure drag, surmounting the increased skin friction to provide the riders with that extra bit of oomph.</p>
<p>Any loose “flapping” material from the riders’ skin suits also causes air separation. By 3D laser scanning athletes, the suit manufacturers can create bespoke, close-fitting suits for each rider, reducing the amount of loose material. 3D scans can also be used in computer simulations to model how air flows over the rider and bobsled in order to analyse where any improvements can be made.</p>
<p><strong>How much of a speed advantage do you think the suits provided?</strong></p>
<p>A very liberal estimate of a 5% reduction in pressure drag would result in an approximate time saving of less than half a second. Most of the drag savings can be made just by an athlete having a sensible, close-fitting skin suit, which most of the athletes already have, further reducing the benefits of the ridges and 3D scanning.</p>
<p>So, the claims of a one-second advantage are exaggerated. But from my experience working in Formula One, it is marginal gains of fractions of a percent that can make the difference to the top athletes. Let’s not forget that Laura Deas only took her bronze by <a href="https://www.olympic.org/pyeongchang-2018/results/resOWG2018/pdf/OWG2018/SKN/OWG2018_SKN_C73B2_SKNWSINGLES-----------------------.pdf">a margin</a> of 0.02 seconds.</p>
<p><strong>Is this fair and if so, why isn’t everyone using them?</strong></p>
<p>The suits were checked by the sport’s governing body and <a href="https://www.theguardian.com/sport/2018/feb/14/rival-athletes-legality-team-gb-skin-suit-winter-olympics">ruled to be legal</a>. Technology plays an important part in sports science. If it is correctly regulated to allow all competitors to profit from it, then this is a good thing. </p>
<p>The research that goes into drag reduction techniques could well be transferable to other engineering disciplines, which could have a benefit to the wider society. </p>
<p>I think that this is just an opportunity missed by other teams. Team GB has clearly invested in the technology aspect of sports. I would like to see more open funding for this type of research, so that more athletes can benefit.</p><img src="https://counter.theconversation.com/content/91936/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Nicholas Martin does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The science behind the suits that gave Britain’s medal-winning athletes a crucial speed boost.Nicholas Martin, Senior Lecturer in Aerodynamics, Northumbria University, NewcastleLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/807952017-08-03T00:59:51Z2017-08-03T00:59:51ZHow hot weather – and climate change – affect airline flights<figure><img src="https://images.theconversation.com/files/180077/original/file-20170727-8486-3gcmgf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">When is it too hot to fly?</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/heat-wave-airplane-airport-665107561">Dmitri Fedorov/Shutterstock.com</a></span></figcaption></figure><p>Hot weather has forced <a href="https://www.washingtonpost.com/news/capital-weather-gang/wp/2017/06/20/its-so-hot-in-phoenix-that-airplanes-cant-fly/">dozens of commercial flights to be canceled</a> at airports in the Southwest this summer. This flight-disrupting heat is a warning sign. Climate change is projected to have far-reaching repercussions – including <a href="http://dx.doi.org/10.1098/rsta.2012.0294">sea level rise inundating cities</a> and shifting weather patterns causing <a href="http://dx.doi.org/10.1073/pnas.0906865106">long-term declines in agricultural yields</a>. And there is evidence that it is beginning to affect the takeoff performance of commercial aircraft, with potential effects on airline costs.</p>
<p>National and global transportation systems and the economic activity they support have been <a href="http://dx.doi.org/10.1038/nature15725">optimized for the climate</a> in which it all developed: Machines are designed to operate in common temperature ranges, logistical plans depend on historical weather patterns and coastal land development is based on <a href="http://cpo.noaa.gov/sites/cpo/Reports/2012/NOAA_SLR_r3.pdf">known flood zones</a>. In the aviation sector, airports and aircraft are designed for the weather conditions experienced historically. Because the climate is changing, even fundamental infrastructure elements like airports and key economic sectors like air transportation may need to be redesigned and reengineered.</p>
<p>As scientists focused on the <a href="http://dx.doi.org/10.1175/WCAS-D-15-0063.1">impacts of climate change and extreme weather</a> on human society and natural ecosystems around the world, our research has quantified how extreme heat associated with our <a href="http://dx.doi.org/10.1007/s10584-017-2018-9">warming climate may affect flights</a> around the world. We’ve found that major airports from New York to Dubai to Bangkok will see more frequent takeoff weight restrictions in the coming decades due to increasingly common hot temperatures.</p>
<h2>Climate changes flights</h2>
<p>There is robust evidence that extreme events such as heat waves and coastal flooding are happening with <a href="http://dx.doi.org/10.1073/pnas.1222469111">greater frequency and intensity</a> than just a few decades ago. And if we fail to reduce greenhouse gas emissions significantly in the next few decades, the frequency and intensity of these extremes is projected to <a href="http://dx.doi.org/10.1002/jgrd.50188">increase dramatically</a>. </p>
<p>The effects on aviation may be widespread. Many airports are built near sea level, putting them <a href="https://doi.org/10.1016/j.trpro.2016.05.036">at risk of more frequent flooding</a> as oceans rise. The frequency and intensity of <a href="http://dx.doi.org/10.1038/nclimate1866">air turbulence may increase</a> in some regions due to <a href="http://dx.doi.org/10.1007/s00376-017-6268-2">strengthening high-altitude winds</a>. Stronger winds would force airlines and pilots to <a href="https://doi.org/10.1088/1748-9326/11/2/024008">modify flight lengths and routings</a>, potentially increasing fuel consumption. </p>
<p>The July heat-related <a href="https://www.circa.com/story/2017/06/20/nation/american-airlines-canceled-flights-in-phoenix-because-its-too-hot-for-planes-to-fly">Phoenix flight cancellations</a> happened at least in part because airlines’ operational manuals didn’t include information for <a href="http://www.fox10phoenix.com/news/arizona-news/262509476-story">temperatures above 118 degrees Fahrenheit</a> – because that kind of heat is historically uncommon. It’s another example of how procedures may need to be updated to adapt to a warmer climate.</p>
<h2>Flying in the heat</h2>
<p>High air temperatures affect the physics of how aircraft fly, meaning aircraft takeoff performance can be <a href="https://doi.org/10.1175/WCAS-D-14-00026.1">impaired on hot days</a>. The amount of lift that an airplane wing generates is affected by the density of the air. Air density in turn depends mostly on air temperature and elevation; higher temperatures and higher elevations both reduce density. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/179073/original/file-20170720-1588-51jqbs.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/179073/original/file-20170720-1588-51jqbs.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/179073/original/file-20170720-1588-51jqbs.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=874&fit=crop&dpr=1 600w, https://images.theconversation.com/files/179073/original/file-20170720-1588-51jqbs.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=874&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/179073/original/file-20170720-1588-51jqbs.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=874&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/179073/original/file-20170720-1588-51jqbs.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1098&fit=crop&dpr=1 754w, https://images.theconversation.com/files/179073/original/file-20170720-1588-51jqbs.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1098&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/179073/original/file-20170720-1588-51jqbs.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1098&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Hot air is less dense than cooler air. That affects the amount of lift an airplane can generate.</span>
<span class="attribution"><span class="source">The Conversation (via Piktochart)</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>The lower the air density, the faster an airplane must travel to produce enough lift to take off. It takes more runway to reach a higher speed, and depending on how long the airport’s runway is, some airplanes might risk running out of room before reaching sufficient speed. When this occurs, the only immediate option is to reduce the aircraft’s weight to lower its required takeoff speed – by removing passengers, luggage and cargo. This is referred to as a weight restriction. </p>
<p>Weight restrictions happen now, especially in hot places like Phoenix and <a href="http://www.ldeo.columbia.edu/news-events/surging-heat-may-limit-aircraft-takeoffs-globally">Dubai</a> and at airports with short runways like <a href="https://www.wsj.com/articles/la-guardias-runways-come-up-short-1479078957">New York’s LaGuardia</a> and Washington, D.C.’s Reagan National, but our research suggests that they may become much more common in the future. </p>
<p>Global temperatures have been <a href="https://www.ipcc.ch/report/ar5/wg1/">steadily rising for decades</a>, and they will almost certainly continue to do so. In some regions, there is evidence that the <a href="http://dx.doi.org/10.1002/2015GL064914">hottest temperatures may increase at a faster rate</a> than the average, <a href="http://dx.doi.org/10.1007/s40641-016-0042-x">further stacking the deck</a> in favor of extreme heat. These hotter temperatures will reduce air density and make it much more likely weight restrictions are needed for flights taking off during the hottest parts of the day. </p>
<p>The frequency and magnitude of weight restrictions is projected to increase – in some locations, the number of days requiring at least some amount of weight restriction for certain aircraft could double or triple, perhaps covering 50 or more days per year.</p>
<h2>The economics of adaptation</h2>
<p>On most affected flights, the amount of cargo, passengers and fuel that must be removed to allow for takeoff will usually be small – between 0.5 percent and 4 percent of the total load. That means fewer paying customers on airplanes, and less cargo on board. When those restrictions add up across the global air transport system, the costs can be significant.</p>
<p>Carrying just a fraction of a percent fewer passengers or less cargo can add up to <a href="https://www.wired.com/2012/09/how-can-airlines-reduce-fuel-costs/">millions of dollars in lost revenue</a> for an airline over years of operation. That makes even small weight restrictions a concern in such a highly competitive and optimized industry. These limits could disproportionately affect <a href="https://www.ft.com/content/689a1618-814d-11e5-8095-ed1a37d1e096">long-haul flights</a>, which require large fuel loads and often take off near their maximum weights.</p>
<p>There are ways that airlines could mitigate increasing weight restrictions. The most feasible is to reschedule some flights to cooler hours of the day – although with <a href="http://www.iata.org/pressroom/pr/Pages/2016-10-18-02.aspx">air traffic increasing</a> and many airports already <a href="http://www.accessmagazine.org/spring-2016/manage-flight-demand-or-build-airport-capacity/">operating near capacity</a>, this could prove difficult. </p>
<p>Another potential solution is to build longer runways. But that’s not always possible: Some airports, like New York’s LaGuardia, are on coastlines or in dense urban environments. Even where a longer runway is technically possible, buying the land and expanding an airport’s physical area may be <a href="http://www.bbc.com/news/business-35011620">expensive and politically difficult</a>.</p>
<p>Aircraft could be optimized for takeoff performance, but redesigning aircraft is <a href="http://www.seattletimes.com/business/boeing-aerospace/will-787-program-ever-show-an-overall-profit-analysts-grow-more-skeptical/">extremely expensive and can take decades</a>. <a href="http://www.boeing.com/features/2016/01/innovation-777-lighter-01-16.page">Manufacturers are always working</a> to build planes that are <a href="https://www.wired.com/2015/06/planes-get-efficient-heres/">lighter and more fuel-efficient</a>. In the future, those efficiency improvements will be necessary just to maintain today’s performance.</p>
<h2>Broader implications</h2>
<p>These changes are merely examples of the countless procedures, processes and equipment requirements that will have to be adjusted for a changing climate. Even if those adaptations are successful, they will take effort and money to achieve.</p>
<p>Many sectors of the economy, including the aviation industry, have yet to seriously consider the effects of climate change. The sooner, the better: Both airport construction and aircraft design take decades, and have lasting effects. Today’s newest planes may well be <a href="http://www.airspacemag.com/need-to-know/what-determines-an-airplanes-lifespan-29533465/">flying in 40 or 50 years</a>, and their replacements are being designed now. The earlier climate impacts are understood and appreciated, the more effective and less costly adaptations can be. Those adaptations may even include innovative ways to dramatically reduce climate-altering emissions across the aviation sector, which would help reduce the problem while also responding to it.</p><img src="https://counter.theconversation.com/content/80795/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Major airports around the world will see more frequent flight restrictions in the coming decades because of increasingly common hot temperatures.Ethan D. Coffel, Ph.D. Student in Earth & Environmental Sciences, Columbia UniversityRadley Horton, Associate Research Scientist, Center for Climate Systems Research, Columbia UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/617002016-06-28T10:16:26Z2016-06-28T10:16:26ZFootball: aerodynamics of the perfect free kick<p>Football has seen many innovations during its <a href="http://www.fifa.com/about-fifa/who-we-are/the-game/">150-year history</a>. But few have affected the game as profoundly as technological changes to the aerodynamic properties of the ball. For nearly 40 years the ball’s panel pattern followed the classic hexagon-pentagon format with 32 panels, but in 2006 the design changed radically. </p>
<p>In the World Cup in Germany that year, the Teamgeist ball had only 14 panels. Then in South Africa 2010 the Jabulani ball featured only eight, and in Brazil 2014 there were just six on the Brazuca. The ball being used at Euro 2016 in France, the Beau Jeu, is essentially a derivative of the Brazuca with identical panel design, so for the moment six appears to be the ideal number of panels.</p>
<p>The panel configuration of a ball <a href="https://plus.maths.org/content/fly-walks-round-football">influences its speed and flight through the air</a>. Problems with the German Teamgeist ball, such as its erratic behaviour in flight, have now largely been eliminated in its successors. But what the subsequent technology has produced is a ball with much reduced aerodynamic drag, which means it flies faster, and stays in the air longer. Enhanced speed is highly desirable in penalty kicks, but not for that other important football set piece: the direct free kick. Here the objective is to <a href="https://plus.maths.org/content/free-kick-football-blink-and-youll-miss-it">beat the defensive wall</a>, to get the ball “up and down” to use the jargon of football’s television pundits.</p>
<p>Getting the ball over the wall is not especially a problem, but bringing the modern ball down sufficiently quickly to commit the goal keeper into making a save is another matter, unless a special kicking technique is used. And this is when the kicker needs to produce the right kind of spin.</p>
<p>A ball in flight experiences three important forces: gravity (the ball’s weight); aerodynamic drag caused by air flowing across its surface; and a special force experienced only when the ball spins. This is called the <a href="http://www.britannica.com/science/Magnus-effect">Magnus force</a> after its discoverer, the German physicist HG Magnus. It has the special property that it is always perpendicular to the <a href="https://plus.maths.org/content/if-you-cant-bend-it-model-it">spin axis of the ball and its forward direction</a>. </p>
<p>The graphic below shows the different kinds of spin a player might impart on the ball, depending on the kicking action adopted.</p>
<p>When backspin is applied, the ball rises quickly. This is the technique used by goalkeepers in kicking for distance, say 60–70 metres, but it’s absolutely useless in free kicks, which are typically taken 20–30 metres from the goal.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/128352/original/image-20160627-28358-161tbl1.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/128352/original/image-20160627-28358-161tbl1.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=180&fit=crop&dpr=1 600w, https://images.theconversation.com/files/128352/original/image-20160627-28358-161tbl1.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=180&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/128352/original/image-20160627-28358-161tbl1.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=180&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/128352/original/image-20160627-28358-161tbl1.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=227&fit=crop&dpr=1 754w, https://images.theconversation.com/files/128352/original/image-20160627-28358-161tbl1.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=227&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/128352/original/image-20160627-28358-161tbl1.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=227&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Types of spin.</span>
<span class="attribution"><span class="source">K.Bray</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Sidespin is the overwhelming preference for the game’s elite kickers, but this is where problems can be encountered. The sideways Magnus force that is produced when perfect sidespin is applied can take the ball beyond a goalkeeper’s diving reach. But crucially, it must descend quickly enough after clearing the defensive wall to force a save. Sidespin does nothing to bring the ball down, which is why so many free kicks of this type are simply ballooned over the crossbar.</p>
<p>Topspin requires a special kicking technique and few players in the modern game can strike a ball, from the ground, in this manner. Even moderate topspin produces a downward-pointing Magnus force, which is very effective in bringing the ball down quickly. There is the further advantage that the ball can be hit harder and with increased initial elevation to ensure that it clears the defensive wall, even though the defenders jump in attempting to block the shot.</p>
<h2>Spin ball wizard</h2>
<p>Now look at the effect that the various types of spin can have on the flight of a free kick. This diagram shows sidespin and topspin free kicks using published aerodynamic data for the Euro 2016 ball. Both shots are hit at 28 metres/sec (63mph) at an elevation that just clears the defensive wall. This is a conservative kicking speed and shots of over 70mph are not uncommon.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/128353/original/image-20160627-28373-1rmhfx3.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/128353/original/image-20160627-28373-1rmhfx3.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=170&fit=crop&dpr=1 600w, https://images.theconversation.com/files/128353/original/image-20160627-28373-1rmhfx3.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=170&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/128353/original/image-20160627-28373-1rmhfx3.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=170&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/128353/original/image-20160627-28373-1rmhfx3.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=214&fit=crop&dpr=1 754w, https://images.theconversation.com/files/128353/original/image-20160627-28373-1rmhfx3.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=214&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/128353/original/image-20160627-28373-1rmhfx3.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=214&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Ball flight.</span>
<span class="attribution"><span class="source">K.Bray</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>As the graphic above shows a sidespin free kick is no threat for distances closer than 25 metres, whereas topspin is effective from as close as 20 metres - and perhaps a little closer - to the goal.</p>
<p>So what are the lessons here for footballers? Well, sidespin can be still be used if the shot is under-hit to keep the speed down, to ensure the ball arrives on target. But this is not easy to do when the adrenaline is flowing. Or the limitations of this technique can be accepted, and if a full-blooded delivery is intended, it can be restricted to longer range efforts, say beyond 25 metres.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/TSv1GL3lwm8?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>Alternatively strikers can do their best to emulate the superb technique of Wales’ Gareth Bale who has mastered the skill necessary to hit a ball with pace and topspin from the ground. Anyone who doubts this should look carefully at the ball’s rotation in the many slow motion replays of his wonderful free kick against England at Euro 2016. It is pure topspin beyond question. And whether he knows the maths behind it or not, there can be little doubt that he has discovered a winning formula.</p><img src="https://counter.theconversation.com/content/61700/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Ken Bray does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The science behind a successful set piece.Ken Bray, Senior Visiting Fellow, University of BathLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/605842016-06-24T21:40:18Z2016-06-24T21:40:18ZCould dragons on Westeros fly? Aeronautical engineering and maths say they could<p>Like many people, I have recently become fascinated the lives and loves of the ruling classes of the people of Westeros, where the occasionally charming inhabitants spend a lot of time bickering about who is in charge. <a href="https://hbo.co.uk/game-of-thrones">Game of Thrones</a> is very entertaining – but don’t get attached to any of the characters, as the lifespan in their world does seem quite variable.</p>
<p>One of the many aspiring rulers – <a href="http://gameofthrones.wikia.com/wiki/Daenerys_Targaryen">Daenerys Targaryen</a> – spends a fair bit of her time around and occasionally riding dragons. My background as an <a href="http://www.bls.gov/oes/current/oes172011.htm">aeronautical engineer</a> got me thinking <a href="http://www.draconian.com/history/history.htm">about the mythical creatures</a> and it struck me that in order to fly, their world must work a bit differently compared to Earth. </p>
<p>It’s possible to estimate the size of a dragon by comparison to Daenerys who looks to be about 1.6m (5ft 3in) tall with a mass of around 60kg (132lb). The dragon’s body seems to be about four times as long as her, around five times as deep, and about twice as wide, with a tail about the same length again and about as thick as her body. Assuming the density of dragon and woman are about the same then a fully grown dragon’s mass must be around 44 times that of Daenerys: around 2,600kg (5,700lb).</p>
<p>Considering everyone in Westeros seems to move in a similar way to us on Earth, let’s assume the same gravitational pull, which puts the dragon’s weight at 26,000 <a href="http://hypertextbook.com/facts/2004/WaiWingLeung.shtml">Newtons</a> (which we’ll call <em>W</em>) at a nominal <a href="http://www.physicsclassroom.com/class/1DKin/Lesson-5/Acceleration-of-Gravity">acceleration due to gravity</a> of ten metres per second per second (32 ft/s/s). </p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/128031/original/image-20160624-28349-16ddnnx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/128031/original/image-20160624-28349-16ddnnx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=800&fit=crop&dpr=1 600w, https://images.theconversation.com/files/128031/original/image-20160624-28349-16ddnnx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=800&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/128031/original/image-20160624-28349-16ddnnx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=800&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/128031/original/image-20160624-28349-16ddnnx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1005&fit=crop&dpr=1 754w, https://images.theconversation.com/files/128031/original/image-20160624-28349-16ddnnx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1005&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/128031/original/image-20160624-28349-16ddnnx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1005&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Daenerys Targaryen, often seen on the back of a dragon.</span>
<span class="attribution"><a class="source" href="http://brentonmb.deviantart.com/art/Daenerys-Targaryen-544405755">brentonmb</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>If we’re to understand the <a href="http://www.nasa.gov/audience/forstudents/5-8/features/nasa-knows/what-is-aerodynamics-58.html">aerodynamics</a> of flying dragons, we need two more bits of information. First, the wing area. Each wing seems to have a span roughly twice the dragon’s main body length, so let’s approximate the wings as two rectangles 4m by 8m (13 by 26ft), or 64m<sup>2</sup> (340ft), which we’ll call <em>S</em>. </p>
<p>Second, the <a href="http://www.experimentalaircraft.info/flight-planning/aircraft-stall-speed-1.php">stalling speed</a>, or slowest that the dragon can safely fly before it falls out of the sky. It would be reasonable to guess that dragons take off and land at roughly their stalling speed, just as aeroplanes and birds do. Judging by the programmes it seems that the dragon’s body-length of about 13m passes by in about three seconds, which puts the stalling speed at about 4.3 m/s or 14 ft/s.</p>
<h2>Dragon aerodynamics</h2>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/127943/original/image-20160623-30267-1pw1ghe.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/127943/original/image-20160623-30267-1pw1ghe.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=201&fit=crop&dpr=1 600w, https://images.theconversation.com/files/127943/original/image-20160623-30267-1pw1ghe.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=201&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/127943/original/image-20160623-30267-1pw1ghe.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=201&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/127943/original/image-20160623-30267-1pw1ghe.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=253&fit=crop&dpr=1 754w, https://images.theconversation.com/files/127943/original/image-20160623-30267-1pw1ghe.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=253&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/127943/original/image-20160623-30267-1pw1ghe.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=253&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<p>As an engineer, when presented with any problem I usually to resort to <a href="http://angelasaini.blogspot.co.uk/2008/06/apparently-maths-is-useless.html">mathematics</a>, in this case the <a href="http://www.experimentalaircraft.info/flight-planning/aircraft-lift-formula.php">standard lift equation</a> of:</p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/127944/original/image-20160623-30259-hiizfb.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/127944/original/image-20160623-30259-hiizfb.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=266&fit=crop&dpr=1 600w, https://images.theconversation.com/files/127944/original/image-20160623-30259-hiizfb.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=266&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/127944/original/image-20160623-30259-hiizfb.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=266&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/127944/original/image-20160623-30259-hiizfb.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=335&fit=crop&dpr=1 754w, https://images.theconversation.com/files/127944/original/image-20160623-30259-hiizfb.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=335&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/127944/original/image-20160623-30259-hiizfb.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=335&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<p>which I can re-arrange to:-</p>
<p>If we use the standard <a href="http://www.universalweather.com/blog/2014/09/international-standard-atmosphere-how-it-affects-flight-understanding-the-basics/">earth sea-level</a> air density of <em>ρ</em> = 1.2kg/m<sup>3,</sup> this gives a <a href="https://sites.google.com/site/aerodynamics4students/table-of-contents/aircraft-performance-1/lift-and-lifrt-coefficient">lift coefficient</a> of 36. Which is completely unrealistic. </p>
<p>By comparison, a <a href="http://www.latimes.com/local/obituaries/la-me-francis-rogallo10-2009sep10-story.html">Rogallo winged microlight aeroplane</a> – a tiny single or two-seater aeroplane comprising a light frame and a small engine suspended below a hang gliding-style textile wing – would have a lift coefficient of between 2.2 and 2.7. No doubt evolution has adapted the dragon’s wing to be highly efficient, but I had to make some assumptions here, so went for a maximum lift coefficient (or C<sub>L.max</sub>) of 3.5.</p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/127946/original/image-20160623-30278-1qmcrrh.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/127946/original/image-20160623-30278-1qmcrrh.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=158&fit=crop&dpr=1 600w, https://images.theconversation.com/files/127946/original/image-20160623-30278-1qmcrrh.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=158&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/127946/original/image-20160623-30278-1qmcrrh.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=158&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/127946/original/image-20160623-30278-1qmcrrh.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=198&fit=crop&dpr=1 754w, https://images.theconversation.com/files/127946/original/image-20160623-30278-1qmcrrh.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=198&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/127946/original/image-20160623-30278-1qmcrrh.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=198&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
</figcaption>
</figure>
<p>Disregarding the possibility of <a href="http://io9.gizmodo.com/technology-isnt-magic-why-clarkes-third-law-always-bug-479194151">magic</a>, this tells us that the atmosphere of Westeros must be far more dense than ours. Using the same figures, we can work out just how dense:</p>
<p>12 kg/m<sup>3,</sup> or about 10 timesthat Earth normal (we call that 10 bar) sounds unpleasantly high, but actually isn’t that bad. It’s about what a diver would experience at <a href="http://www.telegraph.co.uk/sport/olympics/diving/5443180/Sara-Campbell-working-under-pressure.html">100 metres depth</a> – perfectly survivable.</p>
<p>There’s empirical evidence that supports this. Watching a few episodes of Game of Thrones you’ll notice that pretty much anybody can pick up a spear or sword and throw it distances that an <a href="https://ojs.ub.uni-konstanz.de/cpa/article/viewFile/2340/2206">Olympic javelin thrower</a> would be deeply envious of. Given that gravity seems to be roughly similar to ours, this suggests the thrown weapons are generating much more lift than on Earth – consistent with an atmosphere of higher density.</p>
<h2>There’s something in the air</h2>
<p>What is the mix of gases in this atmosphere, I wondered? Earth’s atmosphere is 21% oxygen, 78% nitrogen, and 1% various other gases. We know that 21% oxygen is fine – you and I are breathing it at the moment – while 30% oxygen concentrations causes just about everything <a href="https://www.boconline.co.uk/en/sheq/gas-safety/gas-risks/oxygen-gas-risks/oxygen-gas-risks.html">to become highly flammable</a> (beyond that starts to verge on explosive). This seems quite likely on Westeros, as anybody going near the slightest puff of dragon breath seems to catch fire, while it’s noticeable that most of the locals are all paranoid about lighting fires anywhere except inside a stone castle. Westeros probably has a high-density air with around 30% oxygen, but no more. </p>
<p>What of the rest? I’m going to hazard an educated guess here that it may not be nitrogen that we’re used to on Earth, but is instead <a href="http://www.chemicool.com/elements/argon.html">argon</a> – an inert gas which is the next most common gas on earth after <a href="http://www.chemicool.com/elements/argon.html">nitrogen</a>. Argon is 42% more dense than nitrogen and would allow a higher-density atmosphere at a pressure a bit lower than 10 bar.</p>
<p>There are two laws relating to gases that can be used here to work out the behaviour of the air mix of argon and oxygen: <a href="http://scienceprimer.com/charles-law">Charles’ Law</a> to add the components up, and <a href="http://scienceprimer.com/boyles-law">Boyle’s Law</a> to show what happens when the pressure increases. Applying these I can show that at about seven atmosphere’s pressure, a 70% argon, 30% oxygen atmosphere has our air density of 12kg/m<sup>3,</sup> and so dragons can fly. In simple terms - we can have a more dense atmosphere if the air is heavier - in this case by replacing the inert nitrogen we have on earth with the heavier (or more accurately, denser) argon.</p>
<p>This <a href="http://walrussen.nl/sites/default/files/documents/exotic_gases.pdf">argon-oxygen</a> (or <em>argox</em>) mix will actually be <a href="http://medicalgasresearch.biomedcentral.com/articles/10.1186/2045-9912-4-3">moderately narcotic</a> when breathed at high pressures. Perhaps this might in part explain the regularly irrational and downright aggressive behaviour seen among many citizens of Westeros. </p>
<p>So a bit of basic physics, aerodynamics, and some working knowledge of human physiology can tell you a lot about Westeros – where dragons fly, fire is to be feared, and the people’s irrational behaviour is not necessarily down to what they’re drinking, but what they’re breathing.</p><img src="https://counter.theconversation.com/content/60584/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Guy Gratton is an aerospace engineering academic, who sometimes is paid to write or appear in the media on aviation matters, or to fly aeroplanes. This article is based, with permission, upon one which previously appeared in Global Aviator Magazine. He knows that Westeros isn’t real, but the maths and science in this article are.</span></em></p>Physics says Game of Thrones dragons can fly. Whoever said maths was useless?Guy Gratton, Visiting Senior Research Fellow in Aeronautics, Brunel University LondonLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/532202016-04-24T14:01:59Z2016-04-24T14:01:59ZDo wind vent holes in banners make a difference? We used a wind tunnel to find out<p>The next time you see a banner hung across a street or from a bridge, or hoisted as part of a street march, protest or demonstration, take a closer look. You may see that the banner has holes or slits cut into it.</p>
<p>But why would someone cut holes into a perfectly good banner?</p>
<p>These are so-called “wind vents”, and for some reason people have been mutilating their banners with these holes in the belief that their presence will significantly reduce the wind loading on the banner.</p>
<p>But does a banner with holes or slits really have an easier time in the wind than an equivalent banner that is hole free?</p>
<h2>History and legislation</h2>
<p>It is not known when people started to cut holes into their banners. There is very little written about the practice, and much of the knowledge appears to come via word of mouth or has been transferred from other wind related domains.</p>
<p>What is obvious from the <a href="http://www.simplysignsandbanners.com/1/post/2011/05/wind-slits-are-they-effective.html">websites of the world’s sign and banner makers</a> is that they are <a href="http://boeksigns.com/banner-wind-vents/">frustrated with having to cut holes into their lovingly-made creations</a>.</p>
<p>Some banner makers <a href="https://www.esigns.com/wind-slits.html">simply refuse</a>, and tell their customers that if they want holes, then they can cut them themselves.</p>
<p>The apparent importance of banner wind vents has led some local governments around the world to make them mandatory for banners installed in certain locations. No vent holes, no banner allowed!</p>
<p>The <a href="http://www.brisbane.qld.gov.au/laws-permits/laws-permits-businesses/light-brisbane-hang-bridge-banner/lighting-banner-packages/guidelines-hanging-bridge-banner">regulations of the Brisbane City Council</a>, in Queensland, Australia, state that for banners to be installed on the city’s iconic Story Bridge, they “must be provided with wind vent holes” and that “wind holes (vents) need to be spaced at approx. 3m intervals”.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/116452/original/image-20160325-17859-p641wg.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/116452/original/image-20160325-17859-p641wg.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/116452/original/image-20160325-17859-p641wg.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=169&fit=crop&dpr=1 600w, https://images.theconversation.com/files/116452/original/image-20160325-17859-p641wg.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=169&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/116452/original/image-20160325-17859-p641wg.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=169&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/116452/original/image-20160325-17859-p641wg.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=212&fit=crop&dpr=1 754w, https://images.theconversation.com/files/116452/original/image-20160325-17859-p641wg.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=212&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/116452/original/image-20160325-17859-p641wg.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=212&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Brisbane City Council’s Story Bridge banner design guide indicating location of ‘wind vent holes’.</span>
<span class="attribution"><span class="source">Brisbane City Council design guide</span></span>
</figcaption>
</figure>
<p>The small town of Springville, Utah, USA, states in <a href="http://www.springville.org/wp-content/uploads/2015/03/BannerInfoAppPacket.pdf">its regulations</a> that at least 20% of the area of the banner must be made up of holes. It suggests “half moon shaped vents 4-6 inches wide and facing down throughout the banner”.</p>
<h2>Understanding the aerodynamics</h2>
<p>To understand what, if anything, wind vents do for our banners, we need to visit the work of aerodynamics specialists.</p>
<p>In 1956, B. G. de Bray, an aerodynamics expert at the UK’s Royal Aircraft Establishment, performed <a href="http://naca.central.cranfield.ac.uk/reports/arc/cp/0323.pdf">a series of wind tunnel tests</a> to show how flat plates with holes in them performed in a moving air stream. He was interested in how plates could be used for airbrakes on aircraft as they land.</p>
<p>His experiments showed that perforations (holes) make the air flow more stable but that there was “only a comparatively small reduction in drag coefficient”. He shows a graph recording the relationship between the area of the holes and the change in drag coefficient of a flat plate. The graph indicates that making 20% of a banner’s area holes will reduce the drag by around 5% in a wind of 150km/h.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/116451/original/image-20160325-17840-10iy0tz.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/116451/original/image-20160325-17840-10iy0tz.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/116451/original/image-20160325-17840-10iy0tz.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=251&fit=crop&dpr=1 600w, https://images.theconversation.com/files/116451/original/image-20160325-17840-10iy0tz.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=251&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/116451/original/image-20160325-17840-10iy0tz.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=251&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/116451/original/image-20160325-17840-10iy0tz.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=316&fit=crop&dpr=1 754w, https://images.theconversation.com/files/116451/original/image-20160325-17840-10iy0tz.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=316&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/116451/original/image-20160325-17840-10iy0tz.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=316&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">These figures are taken from de Bray’s 1956 work on wind tunnel testing of flat plates with holes and how drag relates to hole area in a 150km/h wind. Note that CD designates the drag coefficient, which is a normalised way of representing force that accounts for plate size (or in our case the banner) and wind speed. Doing this allows the wind tunnel data to be scaled to full-size.</span>
</figcaption>
</figure>
<p>When we consider de Bray’s other finding – that holes do make the air flow more stable – we can look at a common example of this in action in round parachutes.</p>
<p>Billowing structures that fill with air on the windward side, such as round parachutes, become unstable when there are no holes in the structure. The air tends to spill almost randomly from the structure’s edge. This makes the structure flap around in the wind in a seemingly random manner.</p>
<p>This was discovered in the early days of parachute development. In the late 1700s, a number of parachute developers were killed due to accidents relating to their unstable and oscillating chutes.</p>
<p>In 1804, Frenchman Joseph Lelandes invented the apex vent, a hole in the top of the parachute. This appeared to solve the problem of stability but did not appear to reduce the drag, ideal for parachuting where you need the drag.</p>
<p>Since then there have been many studies showing the <a href="http://www.hindawi.com/journals/isrn/2013/320563/">benefits of holes in round parachutes</a>. One group even found during their <a href="https://www.wpi.edu/Pubs/E-project/Available/E-project-042407-112440/unrestricted/Brighenti_Duffen_Head_Vented_Parachutes_MQP.pdf">experiments</a> that vent holes in round parachutes slightly increase the drag on the chute while making it more stable.</p>
<h2>Wind tunnel tests</h2>
<p>Following in de Bray’s footsteps, we decided to turn to wind tunnel experiments to assess just how much impact those holes had on wind forces. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/sIS3Ujk3ytw?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>We conducted a series of simple experiments where we put scaled versions of banners in a wind tunnel and measured the wind forces. We did this for a range of wind speeds and number of vents (holes). We then measured how the forces changed from test to test.</p>
<p>We performed experiments where vents were rectangular holes cut in the fabric and others where the vents were rectangular holes cut on three sides and allowed to hinge at the top (flaps).</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/119728/original/image-20160421-27001-jv64yi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/119728/original/image-20160421-27001-jv64yi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/119728/original/image-20160421-27001-jv64yi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=642&fit=crop&dpr=1 600w, https://images.theconversation.com/files/119728/original/image-20160421-27001-jv64yi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=642&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/119728/original/image-20160421-27001-jv64yi.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=642&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/119728/original/image-20160421-27001-jv64yi.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=807&fit=crop&dpr=1 754w, https://images.theconversation.com/files/119728/original/image-20160421-27001-jv64yi.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=807&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/119728/original/image-20160421-27001-jv64yi.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=807&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A test banner with 7% of its area made of holes in the wind tunnel.</span>
<span class="attribution"><span class="source">Author supplied</span></span>
</figcaption>
</figure>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/119750/original/image-20160422-27007-9magqg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/119750/original/image-20160422-27007-9magqg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/119750/original/image-20160422-27007-9magqg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/119750/original/image-20160422-27007-9magqg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/119750/original/image-20160422-27007-9magqg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/119750/original/image-20160422-27007-9magqg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/119750/original/image-20160422-27007-9magqg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/119750/original/image-20160422-27007-9magqg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">As for above, but showing a banner with 7% porosity and hinged flaps.</span>
<span class="attribution"><span class="source">Author supplied</span></span>
</figcaption>
</figure>
<p>Experimental wind speeds tested ranged from approximately 25km/h to 100km/h and the range of vent hole area to total banner area ratios (porosity) assessed was from zero (no holes in the banner) to approximately 20%, which coincides with the Springville regulations and makes a pretty holy banner.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/119742/original/image-20160422-26976-z94hoe.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/119742/original/image-20160422-26976-z94hoe.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=497&fit=crop&dpr=1 600w, https://images.theconversation.com/files/119742/original/image-20160422-26976-z94hoe.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=497&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/119742/original/image-20160422-26976-z94hoe.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=497&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/119742/original/image-20160422-26976-z94hoe.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=624&fit=crop&dpr=1 754w, https://images.theconversation.com/files/119742/original/image-20160422-26976-z94hoe.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=624&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/119742/original/image-20160422-26976-z94hoe.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=624&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A plot showing drag on the banner versus porosity of the banner for the 100km/h tests over the range of banner porosities. The vertical axis shows the drag coefficient (CD) ratio, which is the wind force measured on the porous banner divided by the wind force on the solid banner. A porosity of 0.1 is 10% holes/vents/flaps.</span>
<span class="attribution"><span class="source">Author supplied</span></span>
</figcaption>
</figure>
<p>A value of 1 in the figure (above) would indicate that the vents have done nothing and a value of 0.9 would suggest there has been a 10% reduction in load.</p>
<p>It is clear that wind vents do reduce the wind load on a banner, but as de Bray showed, the reduction in load is relatively small until porosity becomes large.</p>
<p>The reduction in drag force is greater for holes and hinged flaps than found by de Bray (and others) for uniformly perforated plates or fabrics.</p>
<p>The wind speed makes a difference. At low wind speeds the presence of vents can actually increase the wind load on a banner, which in our test was found to be up to 5%.</p>
<p>In general though, force coefficients decreased as wind speeds increase. This was particularly the case for the banners with flaps, where these vents became more open as the wind speed increased.</p>
<p>So the type of vent makes a big difference. Banners with holes rather than hinged flaps experienced lower wind loads. Both of these vent types experience lower loads than on uniformly perforated plates, which perform similarly to porous mesh fabrics. </p>
<p>With these points in mind, we return to the Brisbane City Council’s regulations for placing banners on the Storey Bridge. It is now possible to calculate the effect of their prescribed wind vents.</p>
<p>If we assume that they would like holes, and the maximum size of a banner is 18m wide by 0.9m high, then our best guess estimate is a semi-circular hole radius of 25cm noting also that five wind holes are required. We calculate that at most, 3% of the banner will be holes.</p>
<p>Interpolating our figure this would give us a 2% reduction in wind load. A sign of 98% the area of the maximum would be 18m wide and 0.88m high and would only require you to trim 2cm off the bottom of the sign to create a sign of equivalent drag to the one with five holes in it! It hardly seems worth the effort.</p>
<h2>The verdict</h2>
<p>The science shows us that flat structures behave one way, and billowing air-filled structures behave a different way. It seems that our legislators have been confused and applied results from parachutes to flat banners.</p>
<p>If you have a banner tied in such a way that it will remain relatively flat in the wind, then it seems that the benefits of putting in vents are minimal unless you make your banner into Swiss cheese.</p>
<p>You are simply better off making a slightly small banner to achieve the same reduction in load.</p><img src="https://counter.theconversation.com/content/53220/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Matthew Mason receives funding from Australian Research Council and the Bushfire and Natural Hazards Cooperative Research Centre. </span></em></p><p class="fine-print"><em><span>Jonathan Roberts is an Associate Investigator with the Australian Centre for Robotic Vision and co-founder of the UAV Challenge flying robot competition. </span></em></p>Attend any ANZAC Day parade and you might see people carrying banners with holes cut in them. They’re supposed to cut any drag or wind resistance but do they do any good?Matthew Mason, Lecturer in Civil Engineering, The University of QueenslandJonathan Roberts, Professor in Robotics, Queensland University of TechnologyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/516242015-12-02T17:47:10Z2015-12-02T17:47:10ZThe design decisions behind Amazon’s strange-looking delivery drone<figure><img src="https://images.theconversation.com/files/103929/original/image-20151201-26544-2kore2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Amazon Prime Air</span></span></figcaption></figure><p>The unusual look of <a href="http://www.bbc.co.uk/news/technology-34963684">Amazon’s delivery drone</a> combines elements of both fixed-wing aircraft, such as traditional passenger aeroplanes, and rotocraft such as helicopters, in a design that looks like neither. But despite its unusual looks the boxy drone has been designed with the requirements of its door-to-door delivery duty in mind.</p>
<p>Rotocraft can take off and land vertically, which will be an essential requirement if the company is to deliver possibly fragile packages safely and precisely as part of its <a href="http://www.amazon.com/b?node=8037720011">Amazon Prime Air service</a>. The downside is their lower efficiency and range. As a hybrid of the two, the Amazon drone allows the convenience of vertical take-off and landing, and with its fixed-wing features, the possibility of smooth and quick flight to deliver packages up to around 15 miles away within 30 minutes.</p>
<p>The rotary element includes eight propellers organised in four pairs of coaxial rotors – where one is mounted over the other – in a quadcopter layout. These are fitted to two horizontal booms, one to either side of the drone’s central torpedo-like fuselage which carries the packages and the batteries to power it. Coaxial rotors are less efficient than single rotor propellers and they require about 40% more power for the same thrust. But they do provide larger thrust for a given rotor area – a way of packing the most thrust into a small-bodied aircraft.</p>
<h2>Power and stability</h2>
<p>The basic principle behind a quadcopter layout is that thrust produced by each of the propellers can be controlled independently to stabilise the attitude of the vehicle. Unlike a helicopter, manual control of a quadcopter is practically impossible. The reason that quadcopters have become so popular – and easy to fly – is only due to the rise of affordable autopilot systems that intelligently monitor and stabilise the drone.</p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/104119/original/image-20151202-22456-y8j8qu.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/104119/original/image-20151202-22456-y8j8qu.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/104119/original/image-20151202-22456-y8j8qu.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=366&fit=crop&dpr=1 600w, https://images.theconversation.com/files/104119/original/image-20151202-22456-y8j8qu.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=366&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/104119/original/image-20151202-22456-y8j8qu.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=366&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/104119/original/image-20151202-22456-y8j8qu.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=459&fit=crop&dpr=1 754w, https://images.theconversation.com/files/104119/original/image-20151202-22456-y8j8qu.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=459&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/104119/original/image-20151202-22456-y8j8qu.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=459&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A box wing design, where the upper and lower wing surfaces ‘wrap around’.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Annular_box_wing.svg">Steelpillow</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>The fixed-wing aspect of the drone is composed of two wings. The rear wing is a box wing design, incorporating three vertical tail fins, one with a horizontally-mounted propeller. While rarely used, box wings are theoretically more efficient than conventional wings due to the reduction of what is known as <a href="https://www.grc.nasa.gov/www/k-12/airplane/induced.html">vortex-induced drag</a>. </p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/103930/original/image-20151201-9279-cw5uk7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/103930/original/image-20151201-9279-cw5uk7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=488&fit=crop&dpr=1 600w, https://images.theconversation.com/files/103930/original/image-20151201-9279-cw5uk7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=488&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/103930/original/image-20151201-9279-cw5uk7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=488&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/103930/original/image-20151201-9279-cw5uk7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=613&fit=crop&dpr=1 754w, https://images.theconversation.com/files/103930/original/image-20151201-9279-cw5uk7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=613&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/103930/original/image-20151201-9279-cw5uk7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=613&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Experiments with smoke reveal strength and size of wingtip vortices.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/File:Airplane_vortex_edit.jpg">NASA</a></span>
</figcaption>
</figure>
<p>This drag occurs due to the high-pressure air on the wing’s lower surface escaping around the wing-tips, causing drag and reducing the effectiveness of the wing. In order to work around this, this the box wing design provides a continuous surface that blocks the movement of air from lower to upper surface. Winglets on conventional aircraft are designed to play a similar role.</p>
<p>The box wing also has some structural advantages, but in practice there are aerodynamic trade-offs which mean it is normally discarded in favour of large wing spans. In Amazon’s case, the box wing design provides the necessary lift in an aircraft that’s also small – so that it’s easier to land in your garden.</p>
<figure class="align-left zoomable">
<a href="https://images.theconversation.com/files/103926/original/image-20151201-26578-1uws5mi.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/103926/original/image-20151201-26578-1uws5mi.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/103926/original/image-20151201-26578-1uws5mi.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/103926/original/image-20151201-26578-1uws5mi.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/103926/original/image-20151201-26578-1uws5mi.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/103926/original/image-20151201-26578-1uws5mi.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/103926/original/image-20151201-26578-1uws5mi.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/103926/original/image-20151201-26578-1uws5mi.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A winglet on the wing tip, designed to reduce drag.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:CO-Winglet.JPG">Hecki</a></span>
</figcaption>
</figure>
<p>The front wing also features winglet-like fins to reduce drag, only these are inverted to point downwards so that they can also double as a place to fit the landing gear, two wheels, in a way that doesn’t create excessive additional drag.</p>
<p>Conventional fixed-wing aircraft usually have their wings set more or less centrally between the nose and tail, whereas the wings of this drone are positioned at the extreme front and rear, giving the aircraft its curious square appearance. </p>
<p>For an aircraft to be stable and safe to fly, the centre of mass must be positioned in front of the centre of lift. On a conventional aircraft the centre of lift is roughly aligned with the main wings and the aircraft’s weight is nearer the nose. The centre of mass for Amazon’s drone will probably be close to the centre of the aircraft to ensure it is balanced when operating in vertical flight. The use of a larger wing area at the rear will help to bring the centre of lift backwards, behind the centre of mass, to ensure it remains stable in forward flight.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/MXo_d6tNWuY?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
</figure>
<p>For its control surfaces, the drone has elevons – a combination of ailerons (which control aircraft roll) and elevators (which control pitch). When synchronised they can be used to control the aircraft’s angle of pitch up or down, and when moved in opposite directions they control the roll of the aircraft. This design is another decision that potentially reduces mass, cost and complexity, although potentially at the cost of control.</p>
<p>The aircraft is one of several prototypes being evaluated by Amazon, and shows some interesting concepts. Inevitably, there’s a difficult compromise to be struck between the need for vertical take-off and landing and forward flight efficiency. The wings and control surfaces add extra weight, reducing flight time, while the rotors, their motors, and the extra structural elements they require will add more weight and drag, reducing its range. It will be interesting to see how Amazon balance these conflicting requirements as their designs progress.</p><img src="https://counter.theconversation.com/content/51624/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Pejman Iravani receives funding from the Bath Alumni Funding to develop UAVs for undergraduate teaching. </span></em></p><p class="fine-print"><em><span>David Cleaver and Jonathan du Bois do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Amazon’s latest delivery drone looks strange - here’s how it flies.Pejman Iravani, Lecturer in Mechanical Engineering, University of BathDavid Cleaver, Lecturer in Aerospace Engineering, University of BathJonathan du Bois, Lecturer in Electromechanical Engineering, University of BathLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/445222015-07-10T12:44:21Z2015-07-10T12:44:21ZScience says a 17-mile stage might be the Tour de France’s toughest test<figure><img src="https://images.theconversation.com/files/88036/original/image-20150710-16930-1qk4ty2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Keeping it together. Staying out the wind. the TTT at the Giro d'Italia.</span> <span class="attribution"><span class="source">Aukje de Vrijer</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>The Tour de France has been rolling for more than a week now and has finally made it to France in a brutal few days that has seen <a href="http://www.letour.com/le-tour/2015/us/stage-4.html">220km stages</a>, major crashes, cobbles, steep ramps and <a href="http://www.cyclingweekly.co.uk/racing/tour-de-france/tony-martins-abandons-tour-de-france-with-broken-collarbone-181565">broken bones for two race leaders</a>. But perhaps the biggest challenge lies just around the corner in an intriguing Stage 9, where the riders have to cover what looks like a trifling 28km.</p>
<p>The problem is that those 28km come in a <a href="http://www.letour.com/le-tour/2015/us/stage-9.html">lumpy team time trial from Vannes to Plumelec</a>, and include a 2km finish at a 6.2% incline. Normally, that wouldn’t set the heart racing for the main contenders, but this will be an exciting test. Each team must bring five riders to the line together before the clock stops; with Tours sometimes decided by seconds, cooperation is now required for the riders to win.</p>
<h2>Playing hide and seek</h2>
<p>That teamwork is essential in a team time trial was made painfully clear in the recent team time trial at the Dauphiné Liberé, a week-long stage race that is a traditional warm-up event for the three-week romp around France. In a stage comparable to the Stage 9 Tour route, several teams lost one or two riders early in the time trial as the road rose and fell. This is a huge risk, or a huge error, depending on whether it was planned or not. </p>
<p>Simply put, the more riders you have, the less time each of them needs to cycle in the front position, the position where aerodynamic drag is experienced most and most power must be expended to maintain a competitive speed. <a href="https://theconversation.com/the-science-behind-tour-de-frances-hide-and-seek-tactics-29008">In a previous article for The Conversation</a>, I have outlined the benefits of drafting – but these benefits are amplified in the team time trial. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/88037/original/image-20150710-16909-k10ten.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/88037/original/image-20150710-16909-k10ten.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/88037/original/image-20150710-16909-k10ten.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=405&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88037/original/image-20150710-16909-k10ten.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=405&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88037/original/image-20150710-16909-k10ten.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=405&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88037/original/image-20150710-16909-k10ten.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=509&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88037/original/image-20150710-16909-k10ten.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=509&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88037/original/image-20150710-16909-k10ten.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=509&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Preparing for pain. But will they stil be together at the end?</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/dnet/3547245570/in/photolist-6psywo-6pswmJ-nyuPJq-ngZ6rr-nwr1PJ-nybMZM-nAfzwx-nytNQV-nye7XU-nytUkx-ngZ9wh-nye7gy-nyeaif-nAfx58-ngZ8Py-nye8Yw-ngZ9UG-nAfzpP-6pok5H-o2NECq-6pokdB-6pssSy-6poknr-6poqHF-6porLB-6porAV-nxZS95-6psxXm-6pordH-6pooLg-8x22xd-8x1XdS-6pojGz-6pstCW-6pswbW-ojfYRL-8x1Vyq-ooQRbz-8x1U4E-8wYGSF-ooQRxr-8wXXdZ-6poqbH-8wY1Ck-6psyjL-6psw1E-6pss8y-6e5GmV-ngsq9k-ngsxhE">E. Dronkert</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Drafting behind your fellow team member <a href="https://www.exploratorium.edu/cycling/aerodynamics2.html">can lead to at least a 15% reduction in required power output</a> compared to the front rider while cycling at the same velocity. Having a rider behind you <a href="https://www.youtube.com/watch?v=PevpVXelq8A">is of benefit too</a> as it removes the void which acts as a drag to the rear. All this means that drafting is crucial for the team time trial – and riders need to optimise their aerodynamics by riding closely together. At the same time, they will need to share the load of riding in the front position and distribute the team’s energy optimally over the race. That is a tough call to make. Each bump in the road will suit different riders best.</p>
<h2>Aero heroes</h2>
<p>Aerodynamics do not only play a role in drafting, they also play a role in how to optimally pace yourself during a time trial. In scientific literature, a lot <a href="http://www.abcc.co.uk/pace-judgement-in-time-trials/">has been written</a> on pacing a time trial, but that has mostly focused on individual performance. Much less is known about how to pace a team time trial.</p>
<p>So, let’s put you in the skinsuit and aero helmet for a moment. When you are cycling in front position, you can imagine yourself cycling through a big bowl of table-tennis balls: the air molecules. Now imagine that you would like to accelerate and cycle twice as fast through this big bowl of balls: you will hit twice as many balls per second, but also, you will hit them with twice the impact force per ball. This means that the air frictional resistance is four times as large (twice as many balls x hitting them twice as hard). </p>
<p>Using some more biomechanics, the power that is needed to overcome this air-frictional resistance (that has become four times as large) while cycling at a velocity (that has become twice as large) is now eight (4x2) times as large compared the power required to cycle at the original velocity. It sounds exhausting – and it is. </p>
<p>In fact, it means that it requires relatively more power to accelerate above average velocity than it would save to decelerate below average velocity. The below image helps to understand why riding to beat <a href="https://theconversation.com/how-bradley-wiggins-can-break-cyclings-toughest-record-41655">cycling’s world hour record</a>, for example, calls for an evenly paced race rather than variable pace. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/88039/original/image-20150710-17458-142j0ct.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/88039/original/image-20150710-17458-142j0ct.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/88039/original/image-20150710-17458-142j0ct.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88039/original/image-20150710-17458-142j0ct.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88039/original/image-20150710-17458-142j0ct.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88039/original/image-20150710-17458-142j0ct.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88039/original/image-20150710-17458-142j0ct.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88039/original/image-20150710-17458-142j0ct.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Faster is harder.</span>
<span class="attribution"><span class="source">Florentina Hettinga</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<h2>Risk strategy</h2>
<p>Individual time trials have been seen in the Tour de France since 1934 and are a fairly straightforward test of one rider’s ability against another (assuming the weather doesn’t sharply change during the stage). Team time trials, however, demand more debate because the format can clearly favour the strong team, while handicapping strong individual riders who are supported by relatively weaker team mates. We have seen that drafting is crucial, and we have seen that were it possible, an even-paced strategy with each rider taking equal shifts in front would be optimal. As we have hinted at above though, not all riders are equal. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/88045/original/image-20150710-17482-1xb9h8d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/88045/original/image-20150710-17482-1xb9h8d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/88045/original/image-20150710-17482-1xb9h8d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/88045/original/image-20150710-17482-1xb9h8d.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/88045/original/image-20150710-17482-1xb9h8d.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/88045/original/image-20150710-17482-1xb9h8d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/88045/original/image-20150710-17482-1xb9h8d.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/88045/original/image-20150710-17482-1xb9h8d.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">This is a sub-optimal aerodynamic configuration.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/waltarrrrr/8677471122/in/photolist-edNiR5-edL5nJ-edNcHw-hoJkkd-RMsFX-hoJfyG-edG1Wf-9whrZN-rRpmAh-bbmL4M-b7AFwB-9weqx4-g3t14e-kPyfEZ-sgub5w-6y4eGz-bbmJwB-bbmK2F-6f5h7e-bbmJEp-bbmKat-bbmKWR-87WzqW-bbmLb4-bbmKxZ-b7qnVr-bbmKQz-bbmKqx-bbmKhD-bbmJNz-bbmLot-bbmJWn-bbmLhn-bbmKL6-phsxyp-9UDVxf-9MAmDc-edFZPA-bUNft6-9whrsE-ahiLjj-bUNfEB-9weqe2-9weq38-7TQSk6-51vo1j-bUGPce-bUGPjr-9Kuhya-hoJgaG">waltarrrrr</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<p>They are not equally strong, so teams need to think about how to structure the strategy as the team rolls through their turns on the front. Also, not all riders are equally large, and teams need to think about how to position them: better for a small rider to cycle behind a large rider rather than vice versa. And lastly, remember that the time of the fifth rider over line is the time that counts for the win. That offers the possibility of sacrificing riders. They might burn off the weakest riders in the early stages, or keep the weaker climbers as fresh as possible for the final ramp. It can be a huge risk. The Dauphiné Liberé team time trial saw most, if not all, teams arrive at the finish with the bare minimum – and all it takes is a late puncture to bring that strategy crashing down. </p>
<p>The complexity of pacing, strategy, aerodynamics, power and gradient may seem hidden at first glance as the teams glide past in sleek formation, but with so many factors at play, there are so many aspects that can go wrong. It’s unlikely anyone will win have won the Tour once Sunday’s team time trial is over, but don’t be surprised if a couple of contenders have seen their chances slip away.</p><img src="https://counter.theconversation.com/content/44522/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Florentina Hettinga does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Mountains? Pah. 60kph sprints and 220km stages? They’re nothing. The thing most troubling the teas battling for the yellow jersey is this time trial.Florentina Hettinga, Lecturer Sport Science, School of Biological Science, University of EssexLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/416552015-06-02T13:45:49Z2015-06-02T13:45:49ZHow Bradley Wiggins can break cycling’s toughest record<figure><img src="https://images.theconversation.com/files/83645/original/image-20150602-6997-ldxuji.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Wiggo is days away from 60 minutes of pain.</span> <span class="attribution"><span class="source">Sebastien Nogier/EPA</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>The <a href="http://www1.skysports.com/cycling/news/15264/9838682/smashing-hour-world-record-inspiring-cyclist-bradley-wiggins">challenge for Bradley Wiggins</a> is beautifully simple: complete the greatest number of laps of a velodrome track in one hour by pedalling as close as possible to the black racing line. However, the simplicity is deceptive, the pain is intense, and cycling’s hour record requires meticulous preparation in terms of equipment, training and strategy in order to have the best chance of success. </p>
<p>The wind can be a friend to the cyclist, but is more often the foe. This is because the power needed to overcome drag rises in proportion to the cube of velocity, so at 50kmph, more than 90% of the rider’s power output is spent fighting the wind. </p>
<p>A skilled road racer can use the wind to their advantage by <a href="https://theconversation.com/the-science-behind-tour-de-frances-hide-and-seek-tactics-29008">slipstreaming to save energy</a> before choosing the prime moment to attack, but when the rider is alone against the clock there is no place to hide. This is why the time-trial is known as the “race of truth” and the <a href="http://www.cyclingweekly.co.uk/tag/hour-record">hour record</a>, which is held under relatively stable conditions in a velodrome, is possibly the perfect time-trial. </p>
<h2>Marginal gains</h2>
<p>Alex Dowsett is the current holder of the hour record in a year which has seen a glut of attempts after the sport’s governing body <a href="http://www.cyclingweekly.co.uk/news/latest-news/hour-record-rule-change-athletes-hour-scrapped-123397">eased back on the rules</a>. On May 2, <a href="http://movistarteam.com/equipo/alex-dowsett">Dowsett</a> rode to a remarkable distance of 52.937km (Wiggins is targeting <a href="http://www.cyclingweekly.co.uk/news/latest-news/sir-bradley-wiggins-reveals-hour-record-target-distance-174752">55.250km</a>).</p>
<p>I was lucky enough to help <a href="http://www.writtle.ac.uk/pge_PressRelease.cfm?ID=1215">construct the training plan</a> which got Alex there, and the experience offers up some useful insights into just what it takes.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/83649/original/image-20150602-6976-n552gu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/83649/original/image-20150602-6976-n552gu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/83649/original/image-20150602-6976-n552gu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=298&fit=crop&dpr=1 600w, https://images.theconversation.com/files/83649/original/image-20150602-6976-n552gu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=298&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/83649/original/image-20150602-6976-n552gu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=298&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/83649/original/image-20150602-6976-n552gu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=374&fit=crop&dpr=1 754w, https://images.theconversation.com/files/83649/original/image-20150602-6976-n552gu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=374&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/83649/original/image-20150602-6976-n552gu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=374&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">And 52.937 km later, you get to celebrate. Alex Dowsett on the Manchester velodrome.</span>
<span class="attribution"><a class="source" href="http://www.crankphoto.co.uk">Chris Keller-Jackson</a></span>
</figcaption>
</figure>
<p>Since Francesco Moser’s successful attempt in 1984 (51.151 km) when he adopted a special skinsuit, disc wheels and low-profile frame, aerodynamics have featured prominently in the technical preparation. People may remember the intriguing battle between <a href="http://www.cyclingweekly.co.uk/news/battle-of-the-brits-hour-record-heroes-27170">Graeme Obree and Chris Boardman</a> as they traded blows over the record and adopted a range of startling on-bike positions in the pursuit of aerodynamic advantage. </p>
<p>Current rules on equipment and riding position are still strict, so any gains come from refinements that take many hours of wind tunnel testing. But they can be found. </p>
<p>Even something as simple as the skinsuit and socks underwent numerous redesigns for Alex‘s attempt to ensure the fabric and fit produced minimal drag. In fact every possible trick of engineering and physics was afforded Alex from the use of custom aero equipment like the disc wheels, frame, handlebars and helmet through to the use of low viscosity lubricants and ceramic bearings. </p>
<p>We even estimated that by heating the velodrome to 28-29 degrees celsius, the reduction in air density and subsequent drag would more than compensate for any loss of performance due to dehydration – although he did still take the precaution of precooling with an ice jacket.</p>
<h2>Easing off</h2>
<p>Training for the hour is pretty similar to tuning an engine. The key to effective physical preparation is to ensure the training is correctly sequenced and monitored to optimise gains in fitness whilst avoiding overtraining. By employing mostly high volume endurance riding with regular intense intervals and carefully timed races, Alex’s fitness was systematically developed with the goal of generating greater power output for the same blood lactate concentration and heart rate. </p>
<p>However, improvements are often masked by accumulated fatigue so a taper was employed prior to the event whereby training load, but not intensity, was reduced to help recovery without compromising fitness. In spite of research, tapering is still very much an art with many cyclists under-performing if they feel “too fresh”: sometimes as a coach you really can be too good.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/83652/original/image-20150602-6955-kj6bjw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/83652/original/image-20150602-6955-kj6bjw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/83652/original/image-20150602-6955-kj6bjw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/83652/original/image-20150602-6955-kj6bjw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/83652/original/image-20150602-6955-kj6bjw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/83652/original/image-20150602-6955-kj6bjw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/83652/original/image-20150602-6955-kj6bjw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/83652/original/image-20150602-6955-kj6bjw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Looking for a smart start.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/toasty/914441359/in/photolist-2oNKyk-5mfbt4-hNJJvt-p2CD3J-ieksfj-qyfyBh-nJ8eNA-iNxnMX-4D14F1-pC4RX2-ftsRg4-dYoLEK-9Ejxgc-fAzXdg-fDiP6C-2gP5ix-fwEW4n-pEb6uJ-at6dj7-fxU3Eb-fySWhi-pmpLnE-oFn4Ye-qGMSWp-svdL46-pjbLqw-hNFzwm-qaSraY-thMioR-9sXPMk-pYv2Tf-rdEWQB-qXGor6-7NYfve-8MXhjZ-pPVCZw-95rwVx-8oTvmn-r7Q3z1-sodcbE-mqs6dU-q3WdnY-3q2Q57-oTHvBL-qqyV3d-qZ6qJ7-4V6Yux-9kiucX-qu5NHJ-fBkwit">Kenneth Lu</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>The hour record is an aerobic event, in fact the intake of air is pretty crucial you might say. But it also demands a significant contribution from those anaerobic <a href="http://sportsmedicine.about.com/od/anatomyandphysiology/a/MuscleFiberType.htm">Type II muscle fibres</a> which don’t get their energy from oxygen and which are engaged at the tortuous start when the rider is trying to churn a massive gear into life.</p>
<p>Theory states that provided the athlete maintains an even pacing strategy at a power output where heart rate, oxygen uptake and blood lactate concentration remain close to a steady state, then the maximum speed should be achieved. Not only is this sweet spot difficult to judge, but the hour record is raced from a standing start that threatens to immediately over-tax the anaerobic systems which tire quickly. The dilemma for Wiggins will be the same as for every hour record racer: go out too slow and valuable speed is lost; too fast and you are plunged into an oxygen deficit that takes dozens of laps to repay.</p>
<p>The precise mechanisms of fatigue are hotly debated in the literature but what we do know is that as time passes any theoretical steady state is lost: fuel is burnt, <a href="http://www.news-medical.net/health/What-are-Metabolites.aspx">chemicals build up which contribute to exhaustion</a>, water is lost and heat accumulates. </p>
<p>The postural muscles throughout the body which maintain the rider’s unnatural aerodynamic position struggle under the strain of high cornering forces and the fixed wheel becomes an instrument of torture with no break from the relentless rhythm of pedalling – there is no freewheeling relief on a track bike. There is some respite as the bike accelerates through each bend, but this is accompanied by an abrupt drop in speed at the start of the following straight. Consequently, the perception of effort rises and the rider’s willpower to continue and ability to hold the line are tested.</p>
<h2>Pace planning</h2>
<p>And so to the biggest deception of all. During the opening 20 minutes the pace is easily manageable with the freshness of the taper, the warm air, the full aero package and low friction components. The speed is “free” and the temptation to ride too fast is great: many have. The previous record holder, Australia’s Rohan Dennis (52.491km), almost paid the price of an ambitious start to slow significantly later on. And it is not hard to pick out Jack Bobridge’s failed attempt from the chart below.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/83660/original/image-20150602-6990-fhsylv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/83660/original/image-20150602-6990-fhsylv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/83660/original/image-20150602-6990-fhsylv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/83660/original/image-20150602-6990-fhsylv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/83660/original/image-20150602-6990-fhsylv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/83660/original/image-20150602-6990-fhsylv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/83660/original/image-20150602-6990-fhsylv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/83660/original/image-20150602-6990-fhsylv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Comparing the pacing. How the riders have approached this year’s Hour record attempts.</span>
<span class="attribution"><a class="source" href="https://twitter.com/xavierdisley/status/598394274036744192/photo/1">B Xavier Disley, PhD</a></span>
</figcaption>
</figure>
<p>Alex’s hour on the other hand was well-drilled with the pace rehearsed over thousands of training laps. He rode to a strict schedule, never going too deep, never accumulating a debt he could not repay. And in the last third of the race, confident that he had budgeted wisely, he attacked Dennis’s record.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/lIKgYg0xN3c?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Highlights of Rohan Dennis’ record ride.</span></figcaption>
</figure>
<p>Was his a “perfect hour” as it was dubbed by his sponsors, or was it too respectful? Maybe it was the euphoria of success, but Alex didn’t show the usual signs of exhaustion at the finish, even lifting his bike above his head in celebration. What is for certain is that Wiggins, having openly pledged to set a record that will stand for many years, cannot afford to hold anything back, not even in the first 20 minutes.</p><img src="https://counter.theconversation.com/content/41655/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Mark Walker does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Riding a bike for 60 minutes doesn’t sound like the hardest thing in the world, but trying to cover 55km will push the Tour de France winner to the limit.Mark Walker, Deputy Head of the School of Sport, Equine & Animal Sciences, Writtle CollegeLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/295682014-07-24T20:24:26Z2014-07-24T20:24:26ZThe aerodynamics of a Tour de France time trial<figure><img src="https://images.theconversation.com/files/54621/original/78vg4v65-1406090949.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Cyclists in the Monash Wind Tunnel are able to measure the effects of their gear on wind resistance.</span> <span class="attribution"><span class="source">Monash University</span>, <span class="license">Author provided</span></span></figcaption></figure><p>As the <a href="https://theconversation.com/topics/tour-de-france">Tour de France</a> approaches its final days, teams will be looking to place their top riders in the best possible position for the all-important individual time trial in the penultimate stage, where the winner of the Tour is determined.</p>
<p>There’s no better example of the importance of this stage than <a href="https://greglemond.com/">Greg LeMond</a>’s legendary Tour victory in 1989. Fellow rider <a href="http://www.nytimes.com/2010/09/01/sports/cycling/01fignon.html">Laurent Fignon</a> had a 50-second lead heading into the stage, but lost to LeMond by just eight seconds, the smallest winning margin in Tour history. </p>
<p>In 2011, our very own <a href="http://www.cadelevans.com.au/">Cadel Evans</a> gained the yellow jersey in the final time trial stage, <a href="http://www.heraldsun.com.au/sport/evans-seals-tour-de-france/story-fn8s9i81-1226062095558">winning the tour</a> by 94 seconds.</p>
<p>Unlike the gruelling mountain stages the tour is renowned for, the final 2014 individual time trial stage – a 54-kilometre race from <a href="http://www.letour.com/le-tour/2014/us/stage-20.html">Bergerac to Perigueux</a> tomorrow – will take place over relatively flat terrain. </p>
<p>This stage exposes individual riders with no team members to support them across the finish line. It showcases individual speed (typically around 55km/h) and those who can cycle from start to finish in the shortest time possible. </p>
<h2>Cycling to win</h2>
<p>There are two critical factors that govern the time taken for a rider to complete the stage: </p>
<ol>
<li>the power output they sustain over the duration of the course</li>
<li>the magnitude of the resistive forces that oppose their forward motion. </li>
</ol>
<p>At these speeds and with shallow hill gradients, up to 95% of the total resistance is attributed to the aerodynamic drag force. This is why aerodynamics is particularly critical to time trial stages, and why teams invest so many resources in finding ways to minimise drag force. </p>
<p>The drive to improve aerodynamics over the past two decades has impacted the positioning of riders on their bicycles, leading to advances in frame design and equipment geometry. </p>
<p>For the final stage of the Tour, riders will replace their standard road bicycles with more aerodynamically shaped frames and wheels, assume positions of lower aerodynamic drag, and utilise streamlined helmets and skin-suits. </p>
<p>Many attribute Greg LeMond’s famous 1989 victory to a last-minute decision to race with revolutionary time trial bars (which are now standard) and a streamlined helmet.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/54619/original/zn7c3rdq-1406090670.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/54619/original/zn7c3rdq-1406090670.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/54619/original/zn7c3rdq-1406090670.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=384&fit=crop&dpr=1 600w, https://images.theconversation.com/files/54619/original/zn7c3rdq-1406090670.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=384&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/54619/original/zn7c3rdq-1406090670.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=384&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/54619/original/zn7c3rdq-1406090670.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=482&fit=crop&dpr=1 754w, https://images.theconversation.com/files/54619/original/zn7c3rdq-1406090670.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=482&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/54619/original/zn7c3rdq-1406090670.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=482&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">LeMond in 1989. Note his helmet and handlebars.</span>
<span class="attribution"><a class="source" href="http://www.flickr.com/photos/bw94/2927911618/in/photolist-5sJj7N-8CRNuL-4CqiJ7-92qsuC-8uTsbs-xi7Y5-932oQS-92BLG5">BeWePa/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>We now understand that this decision likely provided him with a competitive advantage over Fignon, who rode with the less streamlined standard circular-tubed cow-bars and no helmet.</p>
<h2>Optimising aerodynamics</h2>
<p>To continue to gain a competitive advantage, athletes in the Tour need to take full advantage of the latest research in cycling aerodynamics, which investigates new ways to further reduce aerodynamic drag force and optimise rider position and equipment. </p>
<p>The primary tool used to optimise the aerodynamics of the bicycle-rider system is the wind tunnel, fast becoming a necessity for top-performing teams across the world. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/DeZbrXHa8Qk?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The Monash Wind Tunnel being used in the lead up to the 2012 London Olympics.</span></figcaption>
</figure>
<p>Once these were constructed for the primary purpose of aerospace and automotive applications. However recently we have seen leading bicycle manufactures develop their own wind tunnels in order to optimise the aerodynamic performance of their bicycle designs and cycling teams.</p>
<p>Finely tuned wind tunnel testing simulates different environmental conditions – even the interactions between multiple riders. Current cycling research investigates the complete system and all interactions between the cyclist, their bicycle, and the equipment choices available to them – rather than treating each as a separate component. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/54618/original/bd4rfwkz-1406090288.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/54618/original/bd4rfwkz-1406090288.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/54618/original/bd4rfwkz-1406090288.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/54618/original/bd4rfwkz-1406090288.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/54618/original/bd4rfwkz-1406090288.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/54618/original/bd4rfwkz-1406090288.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/54618/original/bd4rfwkz-1406090288.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/54618/original/bd4rfwkz-1406090288.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=501&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption"></span>
<span class="attribution"><span class="source">Monash University</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>According to David Burton, manager of the <a href="http://www.monash.edu.au/research/infrastructure/platforms/wind.html">Monash Wind Tunnel</a>: </p>
<blockquote>
<p>Aerodynamics is critical to these types of events, which are often reduced to seconds. Using force measurements performed in the wind tunnel, we often see that minor changes in rider position, equipment or test conditions could easily account for the small margins seen over the duration of a 50-kilometre time trial.</p>
</blockquote>
<p>Due to the large role that the aerodynamic forces play in cycling speed, the largest gains in cycling performance are most likely to arise from research that pushes the boundaries of equipment design, rider position and race tactics, with a focus on optimising aerodynamics. </p>
<p>One thing is for certain: aerodynamics will have played a significant part in the success of the rider who comes down the Champs Elysees and is named the winner of the 2014 Tour de France.</p><img src="https://counter.theconversation.com/content/29568/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Timothy Crouch receives funding from the Australian Research Council (project number LP100200090).</span></em></p>As the Tour de France approaches its final days, teams will be looking to place their top riders in the best possible position for the all-important individual time trial in the penultimate stage, where…Timothy Crouch, Experimental Aerodynamicist, Monash UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/243942014-03-14T04:36:00Z2014-03-14T04:36:00ZNose jobs and turbo boosts: Formula 1 car redesign in 2014<p>The big race of the annual Australian <a href="http://www.grandprix.com.au/">Formula 1 Grand Prix</a> is coming up this Sunday at Albert Park, Melbourne – and it marks the beginning of a new era as a new set of rules and regulations are adopted this season. </p>
<p>The new rules will have a massive impact on the main aspects of an F1 race: the way cars sound, drive and look.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/43911/original/yhjf7qyj-1394765900.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/43911/original/yhjf7qyj-1394765900.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/43911/original/yhjf7qyj-1394765900.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=141&fit=crop&dpr=1 600w, https://images.theconversation.com/files/43911/original/yhjf7qyj-1394765900.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=141&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/43911/original/yhjf7qyj-1394765900.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=141&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/43911/original/yhjf7qyj-1394765900.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=177&fit=crop&dpr=1 754w, https://images.theconversation.com/files/43911/original/yhjf7qyj-1394765900.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=177&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/43911/original/yhjf7qyj-1394765900.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=177&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Nice nose job: cars at (left) Melbourne Grand Prix 2013 and (right) at the pre-season test in Spain this year.</span>
<span class="attribution"><span class="source">EPA/Diego Azube/Roman Rios</span></span>
</figcaption>
</figure>
<h2>Safety and fuel efficiency</h2>
<p>This year, teams are only allowed to use 140L of fuel per race and the engine rev limit has been set at 15,000rpm (revolution per minute), as opposed to the 18,000rpm previously allowed. </p>
<p>Also, F1 is switching to 1.6L V6 engines (rather than V8 or V10). However, engine turbo has been allowed again (last used in 1988) which can spin up to 100,000rpm – and, of course, generates an amazing noise. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/43925/original/2w95kr6y-1394769126.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/43925/original/2w95kr6y-1394769126.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/43925/original/2w95kr6y-1394769126.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=500&fit=crop&dpr=1 600w, https://images.theconversation.com/files/43925/original/2w95kr6y-1394769126.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=500&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/43925/original/2w95kr6y-1394769126.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=500&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/43925/original/2w95kr6y-1394769126.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=628&fit=crop&dpr=1 754w, https://images.theconversation.com/files/43925/original/2w95kr6y-1394769126.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=628&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/43925/original/2w95kr6y-1394769126.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=628&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Changes to the 2014 Formula One cars have focused on safety and fuel-efficiency.</span>
<span class="attribution"><span class="source">The Conversation</span></span>
</figcaption>
</figure>
<p>Car engines are now more reliant on hybrid technology, and F1 will look to reduce wasted energy. </p>
<p>The concept of a Kinetic Energy Recovery System (<a href="http://www.formula1.com/inside_f1/understanding_the_sport/8763.html">KERS</a>) was introduced in 2009. It worked by harnessing waste energy (mostly heat) created under braking and transforming it into electricity, which could provide additional power for up to 6.67 seconds per lap. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/43921/original/szgvc2ft-1394768008.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/43921/original/szgvc2ft-1394768008.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/43921/original/szgvc2ft-1394768008.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=662&fit=crop&dpr=1 600w, https://images.theconversation.com/files/43921/original/szgvc2ft-1394768008.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=662&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/43921/original/szgvc2ft-1394768008.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=662&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/43921/original/szgvc2ft-1394768008.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=832&fit=crop&dpr=1 754w, https://images.theconversation.com/files/43921/original/szgvc2ft-1394768008.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=832&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/43921/original/szgvc2ft-1394768008.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=832&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">McLaren’s redesign includes the new ‘anteater’ nose.</span>
<span class="attribution"><span class="source">EPA/Mazen Mahdi</span></span>
</figcaption>
</figure>
<p>Starting this year, teams will be using Energy Recovery Systems (<a href="http://www.formula1.com/inside_f1/understanding_the_sport/8763.html">ERS</a>) which combine twice the power with a performance effect around ten times greater by harvesting waste heat energy from the rear brakes and the turbocharger to charge a battery pack that powers motors.</p>
<p>Teams are also only allowed to use five engines throughout the season before incurring a penalty (as opposed to eight engines last year) which makes reliability a high priority for F1 engineers. </p>
<p>The minimum weight of the car has increased from 642kg to 691kg (without fuel), the maximum fuel that a car can carry for a race is limited to 100kg (compared with around 150-160kg last year) and the fuel flow rate to the engine is restricted to 100kg/hr. There were no such limitations last year adding to the importance of the F1 teams’ strategic planning for each race in 2014.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/hFHmYFlbFn8?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Red Bull F1 team explaining the new rules for 2014.</span></figcaption>
</figure>
<h2>A new look</h2>
<p>The nose height has been dramatically reduced (from 550mm to 185mm) for safety purposes – mainly to prevent cars launching upwards in case they rear-end a racing car in front (see below for video of Mark Webber crashing in Valencia in 2010).</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/6GQ0MBMhDjo?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The lower nose is designed to prevent cars from launching upwards.</span></figcaption>
</figure>
<p>The lower nose design and narrower front wing results in a 20% reduction in downforce. The narrower front wing was put in place for safety purposes to reduce punctures caused by <a href="http://www.formula1-dictionary.net/f_w_endplate.html">end plates</a> damaging competitor’s tyres (which typically happens at the start of the race when all cars barrel into the first corner).</p>
<p>Teams can try to regain lost downforce by redesigning rear suspension elements. This is one of many challenges each team will face and it will be interesting how each team reacts.</p>
<h2>Why F1 racing matters to all of us</h2>
<p>The new rules imposed on F1 teams this year are to be considered as part of the larger shift in the automotive industry. As increasingly tight government regulations around car emissions are introduced <a href="http://en.wikipedia.org/wiki/European_emission_standards">in Europe</a> and <a href="http://en.wikipedia.org/wiki/Corporate_Average_Fuel_Economy">the US</a>, Formula 1 is once again placing itself to be a vehicle for innovation that could trickle down to commercial cars.</p>
<p>Some of the technological advances that we take for granted today were inherited from car racing – such as innovations in suspensions, disc brakes, automatic transmissions, engine efficiency, materials selection and design and safety.</p>
<p>After four years of Red Bull-dominated Formula 1, the 2014 rules have already brought a new direction to the sport. Let’s hope the teams capitalise on these changes.</p><img src="https://counter.theconversation.com/content/24394/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Hamza Bendemra does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The big race of the annual Australian Formula 1 Grand Prix is coming up this Sunday at Albert Park, Melbourne – and it marks the beginning of a new era as a new set of rules and regulations are adopted…Hamza Bendemra, Doctoral Candidate, Engineering, Australian National UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/229852014-03-05T10:29:38Z2014-03-05T10:29:38ZHard Evidence: how will the 2014 World Cup ball swerve?<p>There are now only a few months to go until the biggest sporting event of 2014 – the FIFA World Cup in Brazil – and questions are being asked. Will the <a href="http://www.telegraph.co.uk/sport/football/world-cup/10674397/World-Cup-2014-Stadium-delays-are-threat-to-fans-safety-says-Fifa-head-of-security.html">stadiums</a> be ready? Are the <a href="http://www.reuters.com/article/2014/02/20/us-soccer-world-airlines-idUSBREA1J2B620140220">airports</a> ready for the crowds?</p>
<p>But one matter rises above all others – and may have an impact on the destiny of the cup itself: how will the ball move through the air?</p>
<p>The words “Love me or Lose me” appear beside Adidas’s new World Cup football – <a href="http://www.adidas.co.uk/worldcup">the Brazuca</a> – on billboards the world over. They implore the reader to accept the football for what it is and may be a subtle nod to the controversy which dogged the Brazuca’s ancestors: the Jabulani and Teamgeist.</p>
<p>Since 1970, every World Cup football has been made by Adidas, an ideal opportunity to showcase their latest developments in ball design and technology. In 2006 they took a radical departure from the norm with the Teamgeist. Traditionally, a football is constructed from 32 panels stitched together by hand. The Teamgeist had 14 panels which were glued together with heat (thermally bonded), resulting in a ball more “marble-like” than previous generations. </p>
<p>The change was not only aesthetic. Players using the ball complained of erratic behaviour in flight. For the next World Cup (South Africa, 2010) Adidas had considerably redesigned the ball – the Jabulani – which had only eight thermally bonded panels. Unfortunately, the criticism of the ball was, if anything, louder than it had been four years earlier. Many coaches and players compared the Jabulani to a beach ball which swerves unpredictably.</p>
<p>What, if anything, went wrong? And will the same fate greet the new ball, the Brazuca, which has just six polyurethane panels? Many of the barbs aimed at the previous footballs commented on their unnatural lightness – hence the frequent comparisons to beach balls – but both the Teamgeist and Jabulani are just below the maximum mass limit of 445g (the lower limit is 420g). </p>
<p>Their radical design is different from a standard stitched football in two ways. First, fewer panels mean shorter seams. By my own measurements, a 32-panel football has a seam length of around 405cm, compared to 345cm on the Teamgeist and 203cm on the Jabulani. Second, thermal bonding created a much lower seam profile. A laser-scan of the surface of the Jabulani and a stitched football shows the stitched seam is more than twice as deep as the Jabulani’s. The floating, beach ball-like behaviour of these footballs isn’t because they are light, but because they are smooth.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/41617/original/byy86xr9-1392581383.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/41617/original/byy86xr9-1392581383.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/41617/original/byy86xr9-1392581383.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=455&fit=crop&dpr=1 600w, https://images.theconversation.com/files/41617/original/byy86xr9-1392581383.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=455&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/41617/original/byy86xr9-1392581383.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=455&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/41617/original/byy86xr9-1392581383.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=572&fit=crop&dpr=1 754w, https://images.theconversation.com/files/41617/original/byy86xr9-1392581383.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=572&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/41617/original/byy86xr9-1392581383.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=572&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A laser scanned profile of the seams from a 32-panel stitched football and the adidas Jabulani.</span>
<span class="attribution"><span class="source">John Hart, Centre for Sports Engineering Research, Sheffield Hallam University</span></span>
</figcaption>
</figure>
<p>As air flows over a smooth, sleek object, it hugs the surface until it has passed over it completely, creating very little drag. Air flowing over a ball behaves differently, it separates from the surface, creating an area of low pressure behind it – a wake. The low pressure region creates drag force and slows the ball. At low speeds, the air flow is smooth (laminar) and separates early, creating a large wake and relatively high drag force. As speed increases the air becomes more chaotic (turbulent) which helps it stick to the ball for longer, reducing the size of the wake and lowering drag force.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/41618/original/y8hrbpsv-1392581662.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/41618/original/y8hrbpsv-1392581662.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/41618/original/y8hrbpsv-1392581662.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=221&fit=crop&dpr=1 600w, https://images.theconversation.com/files/41618/original/y8hrbpsv-1392581662.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=221&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/41618/original/y8hrbpsv-1392581662.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=221&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/41618/original/y8hrbpsv-1392581662.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=277&fit=crop&dpr=1 754w, https://images.theconversation.com/files/41618/original/y8hrbpsv-1392581662.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=277&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/41618/original/y8hrbpsv-1392581662.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=277&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The wake behind a scale-model football at low (left image) and high (right image) air speed. The difference in the size of wake is clear.</span>
<span class="attribution"><span class="source">Carre MJ, Goodwill SR, Haake SJ / Proc Inst Mech Eng Part C J Mech Eng Sci.</span></span>
</figcaption>
</figure>
<p>Crucially, the seams of a football disturb the air helping it to enter “low drag” at lower speeds. A perfectly smooth football would be unplayable; high levels of drag would radically alter the behaviour of the ball. In addition, at certain speeds a ball can experience smooth and chaotic air flow over different regions of its surface. The resulting asymmetrical wake creates a force imbalance, pushing the ball in a particular direction. While cricket and baseball players take advantage of this effect to create <a href="http://www.espncricinfo.com/magazine/content/story/258645.html">swing</a>, in football the effect occurs at speeds too low to be useful.</p>
<p>The image below shows the drag behaviour of a 32-panel football, it enters low drag at around 60kmph, at which point the chaotic or smooth method of swerving is mostly unavailable. The swerve in football is generated by <a href="http://physicsbuzz.physicscentral.com/2012/06/perfect-free-kick-and-magnus-effect.html">spinning the ball</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/41619/original/354m87r5-1392581958.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/41619/original/354m87r5-1392581958.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/41619/original/354m87r5-1392581958.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=496&fit=crop&dpr=1 600w, https://images.theconversation.com/files/41619/original/354m87r5-1392581958.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=496&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/41619/original/354m87r5-1392581958.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=496&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/41619/original/354m87r5-1392581958.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=623&fit=crop&dpr=1 754w, https://images.theconversation.com/files/41619/original/354m87r5-1392581958.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=623&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/41619/original/354m87r5-1392581958.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=623&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">How the drag of a 32-panel football (measured as the coefficient of drag) changes with air speed. Data obtained from a wind tunnel.</span>
<span class="attribution"><span class="source">Takeshi Asai, University of Tsukuba, Japan</span></span>
</figcaption>
</figure>
<p>The kind of shots which caused trouble in 2006 and 2010 were flat, because the ball had very little spin. The ball seemed to move unpredictably, suddenly swerving and changing direction. Due to the balls’ smoothness, chaotic or smooth airflow could occur at ball speeds experienced during shots and free kicks. In addition, low spin causes the forces acting on the ball to change direction rapidly and unpredictably, leading to unstable flight. This is equivalent to a particular pitch in baseball called the “<a href="http://baseball.physics.illinois.edu/knuckleball.html">knuckleball</a>”.</p>
<p>This effect can occur with other footballs but importantly, the increased smoothness of the Jabulani and Teamgeist made it occur more frequently, at speeds regularly experienced in play.</p>
<p>Will the new Brazuca behave in the same way? There are a couple of reasons why I don’t expect the same amount of controversy at this World Cup. Although the Brazuca uses the same thermal bonding technology of previous generations, the seams are much deeper. This is obvious when handling the ball and a laser scan shows a depth of 1.56 mm, 50% deeper than our 32-panel ball and three times deeper than the Jabulani.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/41620/original/rxmfwz4b-1392582254.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/41620/original/rxmfwz4b-1392582254.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/41620/original/rxmfwz4b-1392582254.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=252&fit=crop&dpr=1 600w, https://images.theconversation.com/files/41620/original/rxmfwz4b-1392582254.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=252&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/41620/original/rxmfwz4b-1392582254.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=252&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/41620/original/rxmfwz4b-1392582254.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=316&fit=crop&dpr=1 754w, https://images.theconversation.com/files/41620/original/rxmfwz4b-1392582254.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=316&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/41620/original/rxmfwz4b-1392582254.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=316&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The scanned seam profile from the adidas Brazuca.</span>
<span class="attribution"><span class="source">John Hart, Centre for Sports Engineering Research, Sheffield Hallam University.</span></span>
</figcaption>
</figure>
<p>With six panels, the Brazuca has the fewest panels of any World Cup football. However, I measured the seam length to be 327cm, greater than the Jabulani. Each panel <a href="http://www.soccerbible.com/news/general/archive/2013/12/03/adidas-brazuca-world-cup-ball-testing.aspx">resembles a four-armed windmill</a> and doesn’t have the large regions of smoothness present on previous panel designs, which further avoids the chaotic or smooth airflow problem. </p>
<p>To complete the argument, the figure below shows the aerodynamic performance of a 32-panel football, a Brazuca and a Jabulani. Notice how the Brazuca behaves very similarly to the 32-panel football and how the Jabulani doesn’t enter low drag until nearly 90kmph, making it prone to the chaotic or smooth behaviour described earlier.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/41621/original/9drq364d-1392582326.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/41621/original/9drq364d-1392582326.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/41621/original/9drq364d-1392582326.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=496&fit=crop&dpr=1 600w, https://images.theconversation.com/files/41621/original/9drq364d-1392582326.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=496&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/41621/original/9drq364d-1392582326.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=496&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/41621/original/9drq364d-1392582326.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=623&fit=crop&dpr=1 754w, https://images.theconversation.com/files/41621/original/9drq364d-1392582326.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=623&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/41621/original/9drq364d-1392582326.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=623&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The aerodynamic data for a 32-panel football, the adidas Jabulani and the adidas Brazuca. Data obtained from a wind tunnel.</span>
<span class="attribution"><span class="source">Takeshi Asai, University of Tsukuba, Japan</span></span>
</figcaption>
</figure>
<p>It is interesting to note that the frenzied media reports regarding the odd behaviour of the Jabulani died down once the matches had begun in earnest. While players and coaches may well find something to complain about with the Brazuca, it is certainly not a beach ball.</p>
<p><em><a href="https://theconversation.com/topics/hard-evidence">Hard Evidence</a> is a series of articles in which academics use research evidence to tackle the trickiest public policy questions.</em></p><img src="https://counter.theconversation.com/content/22985/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Simon Choppin works for the Centre of Sports Engineering Research, Sheffield Hallam University who consult for adidas.</span></em></p>There are now only a few months to go until the biggest sporting event of 2014 – the FIFA World Cup in Brazil – and questions are being asked. Will the stadiums be ready? Are the airports ready for the…Simon Choppin, Research fellow, Sheffield Hallam UniversityLicensed as Creative Commons – attribution, no derivatives.