Q&A: Why doesn't AeroVelo's speedbike use Golf Ball Dimples? 

yup, correct

Shadowboost - not so, "UFO" are round.... As in a flat golf ball...

not sure about projectiles at high speed. my guess is that there is a lot of research out there, that you can find for free.

possible...but yea, any area in contact with the air provides skin friction, and would be bad. Generally, if you have a big opening in your shape with a pipe going thru the interior, you could have made the whole thing smaller, and get rid some of skin friction. The high pressure areas in the front and low pressure in the back would now be a ring, instead of a circle. Somewhere the air has to be stationary.

Zach Hazen Boundary layer control is a pretty hot topic, that I know nothing about :P. What I know that RC planes have been used as proof of concept for boundary layer plasma actuation, and that it worked really well at keeping the boundary layer attached. Any system we implement would need to be human powered. For this year, we did not bother even looking at it, there were a lot of places we could get easier performance out of the bike and rider. The University of Toronto human powered vehicle design team (which I used to lead) will probably look into it in one of their upcoming ASME bikes.

It looks like it's going to become someone's Master's project.

+Jeremy Priede dimple surfaces have greater surface area than smoother surfaces. As such, they got greater drag if the flow is attached. We are very confident our flow is attached over the whole bike, so there is no reason to use dimples. We are confident of this because our drag in real life is very close to the estimated drag (and we estimate no separation) and if there was any separation, our drag would be much higher, very noticeable so.

Thanks, I had thought that it was turbulence that caused drag, but as you point out - it is separation that causes drag. And turbulence can be used by a golf ball to decrease separation (and thus decrease drag).

+Jeremy Priede nope. I suggest you watch the video again. There are a number of causes for drag, such as skin friction and separation. We got no separation on the bike, so no golf ball dimples are necessary. Skin friction causes drag, and gold ball dimples make it worse. Not only golf ball dimples have more surface area, which causes more skin friction, but they also make the air more turbulent. More turbulent air means faster moving air molecules are able to get closer to the skin of the vehicle, thus increasing the skin drag. So gold ball dimples are always bad, unless you have separation, and are not able to get rid of separation any other way. They are a last resort for cases where the shape cannot be changed.

The myth busters tried this with a car and they were wrong! The dimples made the cars mpg increase

@@VRagusila I'd think that turbulent flow allows outside air to contact turbulent air instead of the skin itself. Air on air contact is much more frictionless than air on a solid

I dont see why they would. They would increase skin drag, but I cant think of a mechanism that would result in more lift... Objects on underside of wings dont seem to affect the lift negatively too much either. All airplanes hang engines, rockets, missiles, fuel tanks, etc under the wing, keeping the top side as clean as possible, with the exception of turbulators.

what tube you talking about?

+John Hogue Drag forces are a small contribution to the energy of a baseball bat.

@@appa609 Regardless with what contributes as a "small contribution," many small contributions create one big one. In theory, yes it will help. If you have the means to do it, do it.

Waylon Jeffery well it’s not clear it will be a net positive contribution. Dumpling the bat is also going to slightly decrease the stiffness if the bat. The overall restitution may go down. And it would certainly cost more. Even if it were right it would be tiny.

dimples work for car-like object, or sphere like object. For an object with a tail that we can shape, it is not going to help. Not worth trying because we know the effects of even thicker tape on the back of the bike, which disturbs the airflow and causes higher drag. Dimples would add even more drag.

Well, the plot gets more density. Thickens is not a technical term :P Different air situations require different measures. If the manifold had any separation, dimples would definitely help. There might not be enough room to make the intake a shape that has no internal separation. The shape being fixed (or at least constrained) then the surface can be made to deal with some of the separated air. For us, we could make a shape with no separation quite easily. So no need to use surface features.

I work in very high end motorsports..( sorry not allowed to disclose where , so your guess where is pretty easy) and not used dimples to date. We say: its a solution for a problem created by yourselve....😄😄

yes, people have tried dimples. It is also attempted on cars, bike helmets, etc. While my understanding might be faulty, none of the other teams that went fast in the last 20 years ever used dimples, and they all tried to achieve the smoothest possible shape. Some experienced racers, such as the world champion for 15 years, Sam Whittingham, can feel the difference between different waxes. The smooth ones are always faster.

Hi, so sorry, I am not saying you personally have a faulty understanding, but the general understanding of why dimples work, may be faulty. I was thinking about fish, such as tuna, and sharks, also sailfish are very fast, but have scales that may also act like the dimples. Perhaps if someone tries the dimples and it turns out to help, there will be more research in dimple shape and size. If you have access to a wind tunnel you will be able to measure and compare the drag forces between a dimpled & smooth shell. No need to go out on the field. May be able to also apply this technology to swimsuits for competitive swimming, if it works.

Sean Rhoades Aerodynamics have a bad habit of working very differently depending on the fluid (air or water), size of objects and speed at which they travel. In water some surface roughness or scales do seem to help in some respects. Swimsuit makers have looked into it, and it is a very active research topic. Small channels on the surface of jet engine cowling seem to work as well, and it is being experimented on by NASA. Unfortunately, our time and budget doesnt allow us to research too many topics simultaneously. Tires and wheel aerodynamics are now our main areas where we think we can get a big advantage. The surface of the bike is as good as we will get it without a big research effort, and all existing evidence points for the air, at the speeds we travel at, smooth surfaces are best.

VRagusila I hope some golf ball company CEO sees these posts and helps your team with some more funds. It could happen!

quite likely on motorbike jackets, but I am not an expert. I find that a lot of new jackets use the back protection to change the shape of the rider, and provide a larger area of attached flow. Pretty neat trick.

Unfortunately you are wrong. Aerodynamics is not really intuitive. It took me a while to understand why mixing fast and slow air, due to turbulence, can bent a curve better than slow air from the laminar air. The trick is to understand that the air right next to the object is perfectly still relative to the object. The goal is to keep the air moving against the object, and not make it move backwards. For example, www.researchgate.net/publication/327793049_The_Effects_of_Reynolds_Number_on_Flow_Separation_of_Naca_Aerofoil is a test showing that separation occurs at higher angles of attack for higher Reynolds numbers, which increase linearly with speed. So faster air can bend the curve better than slow air. My understanding is not perfect, and still trying to find the best way to explain it. Good luck trying to understand it better, it is not simple, nor easy.

@@victorragusila7519 Unfortunately you are wrong.

@@lomasck care to elaborate? I always want to learn more about aerodynamics.

@@victorragusila7519 The problem with Aerodynamics is we cant see it.I think we are always trying to understand it that's why I was watching your video after all.Because I did not understand your explanation I came up with my simpler explanation. Perhaps I am wrong.I guess I was just challenging your story on it.OK .I just looked at some other explanations on RU-vid & have a important Question. Does the ball have to spin in flight.That could change everything.How important is the spin factor ?

@@lomasck The spin would definitely affect things, but I think that is a separate problem. Understanding it without spin is important to help understand it with spin later on. I looked for a few more videos to recommend for you, and because I need a refresher course in Aerodynamics, since i havent looked at it for a few years (off to a new obsession for now). I highly recommend this video, they explain boundary layer better than me, without going into Laminar VS turbulent discussion ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-5zLCofDSt_Q.html The Wiki page on flow separation also has some good info .en.wikipedia.org/wiki/Flow_separation We actually can see aerodynamics. We need a wind tunnel or day with fog, but we can see (with the help of smoke) the way the air behaves. It was probably one of the main tools that helped develop airplanes around the two world wars. I am sure you can find some really good videos of flow around balls or wings. A few points that helped me understand aerodynamics: 1) dont think of air as small balls that move around a wing. A faster small ball is harder to turn, whereas a slow one can turn easily. I think that is why intuitively, it is easy to think that fast air separates easier. 2) Air works more like molasses, it has viscosity. Much smaller than molasses, but it still exists. There is friction between all layers of air, and between air and any object. 3) Separation means air moves backwards over a wing (if we think of the wing as 0 velocity). For a ball going thru the air, it means the air sticks to the ball and travels with it. That is generally BAD. You dont want your ball (or wing) to grab a bunch of air and take it along, that creates lots of drag. You want the air to stay exactly where it was before your wing or ball moved thru it. That would be 0 drag (and impossible). Good luck, it took me a while to find an explanation that made it click for me. I was lucky to have a few classmates that took a lot more aerodynamics courses than me, and were very good at explaining it. Once you understand the effects of boundary layer velocity on pressure and separation, you should be able to derive the effect of spin.

thanks! :)

nah. They tested it on a car. which has a boxy shape. For that, dimples work. For our shape, since we can make it streamlined, it is not necessary.

it does on a car, because a car's exterior shape cannot be changed (much). If the shape is fixed (ball, car, truck) then surface aero devices, such as dimples, turbulators, etc, can help quite a bit. But for our bike we were able to use a nearly-perfect shape, so no need for those band-aid fixes. not sorry. :P