Hi Sheepdog,
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Originally Posted by sheepdog 44
Here are some random thoughts mostly about mitigating crosswind dammage, than finding a perfect solution for it.
I would say increasing the dynamic stability of the bike will gain you a portion. A more advanced independent suspension, steering geometry, wheelbase and weight distribution will improve crosswind stability. Which begs the point that the "optimal" donor bike would need to be modified or custom made. As far as weight distribution, i've seen custom rigs where the driver almost sits over the front wheel. Others have the drive sitting low in the frame.
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I'm not following you on the more advanced suspension. Other than the Hossack,there's not a whole lot you can do. Tony Foale did say in one of his articles that excessive trail was bad in crosswinds. Without making an "Easy Rider" chopper, "sport bikes" have fairly small trail to my limited knowledge of motorcycles.
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Weight is a big deal. There was a nearly completely enclosed motorcycle that drove coast to coast on one large tank of gas. It was more stable full than empty. Electric motorcycles are the best clean sheet approach. You have 200 or more pounds of batteries that can be optimally placed for stability.
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Interesting that you mention weight, maybe the Monotracer's are "so stable" is because of their massive (~1000 lb. + riders) nature and limo-like length wheelbase. Calling them motorcycles is stretching the term in my opinion. I didn't realize at first how big they are until I saw a picture of a motorcycle beside one.
Vetter had to add some weights (18 lbs.) to his nose to damp the transient effects of cross wind gusts. It increased the polar moment of inertia.
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The simplest solution is the Bede Pulse autocycle with two outriggers made from trailer wheels. Making a non optimal form like Vetter's Honda Helix with openings (to counteract sidewinds???) is less effective than adding frontal area in outriggers and doing a completely enclosed streamliner. It would also be more commercially viable in cost and in the low driver skill involved than the Monotracer.
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I read that the outriggers are a problem on the Bede Pulse
http://www.autocycles.org/pulseoutrigger.html They experience high wear. I also understand they are tricky in a spin. A bike just drops which is no better. A relatively narrow motorcycle is appealing for lane splitting, otherwise, just go for a trike which the states recognize as a "motorcycle" for licensing purposes. I'd be reluctant to split lanes if I rode a motorcycle although tempting if stuck in traffic.
Motorcycles have a problem in the rolll axis from cross winds. It's inherent. Trikes don't have a roll axis problem except maybe in severe cornering if they are too narrow.
I'm not crazy about Vetter's gaping sides personally although it probably appeals to his open motorcycle mentality. This was all he could do without some other solution unknown to him. Stall Strips
Remember, he's a motorcycle fairing designer, not a rocket scientist.
I personally think Creasey's Voyagers are something only it's mother could love
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The nose is where you can affect crosswind stability without adversely affecting aerodynamics. I like Teri's thoughts on this. A rounded radiused nose is best for crosswind on cars cause it easily passes air from side to side. but on a tall thin bike you want something that equalizes the air pressure on either side. The wind blowing you is manageable. The suction on the other side, being multiplied by speed is the BIG issue. That is the real root of the problem! Suction, suction, suction!
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On a conventional aircraft wing, the leading edge (nose) is especially critical for lift, that's why it's heated (on jets) or has pneumatic de-icing boots for icing conditions.
Practical considerations dictate streamlined motorcycles have a somewhat bulbous nose (for our bodies behind) compared to the overall length. That being said, I believe some aero fix is required especially on the nose (leading edge). A gaping hole like Vetter's is
one way but not elegant. I don't think there is a perfect solution where cross wind effects disappear since we still have the sideways bluff body to blow around. Remember traditional kites fly with flat surfaces.
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I've thought about small deployable airflaps perpendicular to the airflow to ruin your aerodynamics when neccesary. Crosswinds are not an everyday issue. The last resort would be to just kill your aerodynamics when absolutely neccesary.
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I've had similar thoughts about manually deployed spoilers but Vetter lives in a place where it's an everyday problem. Where I live, the winds blow fairly consistently about 15-25 mph from the south and the roads are not very twisty. Vetter also experiences rapidly switching direction winds as well. Getting caught with your spoilers not deployed could be exciting (in a not good way!)
Theo22 in PM's has said his Evo-like motorcycle (same Honda as Allerts')
Cathelijne » e-motion is controllable in highly turbulent air from passing 18 wheelers. He attributes this to the relatively poor aerodynamics but is willing to give up low drag for less cross wind sensitivity. He chose lower frontal area instead of lower Cd. He said that in over 20 years of designing streamlined velomobiles, he and Allert have concluded that the better the Cd, the more sensitive it is to cross winds. They have over 20 years of experience. Don't discount that lightly.
As I said in my opening post, U2 pilots have a deployable stall strips and spoilers during landing but this is in a phase of flight where much concentration is required (not that the U2 is an easy plane to fly anytime).
I still think there is something that is completely passive automatic like stall strips or similar. They are there all the time and working without any thinking or you could have exotic failure prone electro-mechanical solutions.
-- Teri
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