Sports Aerodynamics #2: Motorbike Wheelies!

Some say… That motorbikes where invented by car designers on half the budget, And that secretly, they found driving on half the number of wheels twice the fun. All we know is, aerodynamics make them both go faster!   Drag But in case of a motorbike, it’s all a bit more difficult. Let’s start with the obvious: Motorbike drag is a disaster: apart from some laminar flow around the front fairings, turbulence is king everywhere else. With open wheels, sharp edges and a driver shifting position every two seconds, it’s a challenge to bring down drag. Over time, people have come up with all sorts of clever ways to shield & streamline the driver. But sidewind sensitivity and practicality are big concerns, as you can perhaps imagine. Pulling wheelies Obviously, drag can be overcome by more power. But with acceleration and drag both trying to flip you over backwards, they add up to make you wheelie even faster. And as cool as that may sound, it’s the sign you’ve reached your maximum acceleration rate. When you’re in a race, that’s not what you want. So imagine there is something that could push the front wheel down onto the ground, that would help a great deal. That’s exactly why over the past years, Ducati and others have been experimenting with front wings on their bikes: although not much, they create downforce on the front wheel, counteracting the torque of acceleration and drag. Cornering The effect of downforce on cornering is a bit more complex though, as the aerodynamic vector tilts together with the lean angle of the bike: the downforce generates more pressure and thus more grip, but it also pushes you outwards. The net effect is only positive with a tire friction coefficient of more than one, or when the rider is leaning more into the corner than the bike itself, keeping the downforce as vertical as possible. More power So once you’ve found a way to put more down power, it’s a matter of generating more of it. But more power means bigger cooling demands, and more cooling means bigger radiators. Unless you can use them more efficiently. Airflow through a radiator is generated by a pressure difference between front and back. Increasing this pressure difference increases the driving forces for this airflow and thus the cooling performance. Computational fluid dynamics simulations allow you to identify or even create a suitable high and low-pressure zone for this purpose. Typically the high-pressure inlet is located at the front of the bike and the low-pressure outlet located on the sides for example.   Comfort Not all bikes are designed to go as fast as possible though: some are there to enjoy miles & miles of highway cruising. Just you, the road, and perhaps a bit of unwanted wind noise. Designing the front windshield and the shape of your helmet are crucial towards reducing noise levels. This noise is in part the result of the turbulent kinetic energy of the airflow being dissipated in the form of noise energy. Simulating the sound power generated in the airflow around the rider greatly helps to understand where this noise is coming from. Heat Another effect of this turbulence is the heat transfer rate: a turbulent flow is much more capable of transferring heat between the rider and the surrounding air. That can be good when you need some chill on a hot summer day but can make you freeze on a cold winter night. And on that bombshell, it’s time to end this second movie on sports aerodynamics! Thanks for watching and don’t forget to click the like button and leave some comments! See you soon! ----------------------------------------------------------------------------------------------------------- Wouter Remmerie Wouter is the Founder of AirShaper, an online, virtual wind tunnel. With this tool and these videos, we want to make aerodynamics accessible to everyone! Interested in more content like this on the field of aerodynamics? Make sure to click that subscribe button, we post new videos every week! Looking for a way to test your Aerodynamics projects without all the hassle and the huge costs coming with it? Check out https://www.AirShaper.com and see how easy it can be!

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