Quote:
Originally Posted by Ken Fry
The Ecomobile was available with a rudder.
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Back to the topic of the windy slope. The concept of an airplane like rudder on the back of a full aero motorcycle makes an interesting thought experiment for my stance on the futility of an extended fin behind the rear wheel for the purpose of straight line tracking in side winds. A big fin in the back makes the bike into an arrow when it is going straight down the road except for the fact that arrows don't have two tires stuck to the road. The rear tire is fixed and can only roll straight ahead so even with the tail fin, your bike is not really like an arrow. The tail fin can only push the rear of the bike with the wind but it is forcing the rear tire to go sideways in order for anything to happen. Now look at the rudder sticking up high above the cg and far behind it like the low fin is. Which way would you actuate the rudder if you were flying the bike and got hit by a side wind? Would you actuate the rudder to amplify the force of the wind at the rear as you are trying to do with the tail fin? Again, this is not an airplane. The rear wheel is stuck to the ground and the most effective way to generate the lateral force needed to push back against the side wind is to LEAN the bike so it is camber thrusting and steering into the wind. You would actually use the high mounted rudder in the opposite direction that the tail fin provides by trying to rudder the top of the bike, even though it is behind the rear wheel, to roll INTO the wind. Think about it. Maybe counter intuitive. The rear of the bike to roll INTO the wind. Do tail fins help anything or are they just adding pressure for the side wind to blow you off of the road? I also wonder what any yawing action that did make it sideways past the tracking rear tire would do to the trail in the front geometry. If you could have the cg at the steering axis it would tend to stay neutral like the arrow. But the cg will probably be closer to midway between the wheels with a feet forward design. The yaw will pivot on the cg, forcing the steering axis laterally into the wind, causing the trail to counter steer and precess and lean the wrong way, with the wind.
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Just thinking out loud in the spirit of advancing the design concepts of a streamlined motorcycle which I believe in 100% and will one day own. I think Allert has the better handling design concept by possibly foregoing perfection in frontal drag to get safer rideability (the weather is terrible where I live but I still ride right through it every day) although his design is very high in the back to gain luggage space.
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I would like to see Craig and Allen truncate their tail fins into a Kamm to see if it is better in side winds as it may still be just as aero. And much easier to back out of the garage.