Like you, I have my experience with cars. I would like to know how negative the caster angle was on the plane. Yes, unlike in cars where the caster angle is positive, and the more positive it is, the better stability, and wheel return. But its harder to turn the wheel. In the nose wheel of a plane, the caster angle is negative, very much like in a shoping cart. But similar principles apply. Stability should improve with a more negative angle, and wheel return to center should be better but it should be harder to turn. In a shopping cart, when the wheel doesn't have a full load, it will also shimmy. Im also curious if the weight of the plane in motion is evenly distributed to all wheels, or is the weight on the nose wheel light. and if the air pressure in the tire was adjusted to compensate for a lighter load. IMHO most common causes for a shimmy like that would be an over inflated tire, a tire out of round, or an unbalanced tire. Also there is a posibility that the wheel was modded in a way that the caster angle was decreased, (moved closer to 0) If everything checks out, Im betting on an over-inflated tire same can be observed in a car when the tires are over-inflated going over a bump, the tire will bounce, and steering wheel will oscilate. I do agree that the wheel pants could amplify the oscilation. In the past open wheel race cars suffered from catastrophic crashes due to aerodynamics on the open wheel. I really dont know anything about airplane landing gear, but am comparing the sympthoms to automotive tech. I do admit, no where on a car or a bike is the wheel caster negative so its hard to compare the two.
"Maybe I should have emphasized caster angle a little more... caster angle (the angle from the vertical pivot point to the contact patch of the tire on the pavement, similar to the trail on a motorcycle) can improve the stability and natural tendency of the tire to track true. I agree with all of the points that Mark L has made, but the video I saw showed the shimmy continuing all the way down the runway... if the caster angle and balance had been properly done, the shimmy would tend to cancel out as the plane went down the runway. Granted, I know more about motorcycles and cars than I do about planes, but once the bird is on the ground, I would think similar rules would apply. Yes damping is important, but if the geometry of the set-up is off, it won't help the shimmy unless the gear is "locked in" (too stiff) which kind of defeats the purpose of a castering nose wheel doesn't it?"
