Shimmy

[dfcullum]

After many years of putting up with main wheel shimmy on my RV-3, and trying a number of solutions, I finally tested the shimmy without wheel pants. Success! No shimmy at any taxi speeds. However, I don't want to fly without the pants, so what can I do? One recommendation was to put weight in the nose of the wheel pants (on the assumption that it was similar to flutter in an unbalanced aileron), but no improvement. Has anyone experienced this problem and found a solution? These are old-style pants. The problem is alleviated if I reduce the tire pressure to 15-17 PSI.

[David Paule]

Do you have the gear leg stiffeners on?

Dave

[Mike S]

Dennis, welcome aboard the good ship VAF

[Vac]

Technical thoughts from the RVator:

Gear Shimmy. With a rod gear leg, the wheels can move fore and aft, so if scrubbing action of the tire is absent, there is no damping and a fore and aft shimmy can result. This is most prevalent at low speeds (10-15 mph) on a paved surface. Turf surfaces (generally) have sufficient rolling resistance to provide a damping action. Out of balance wheels and higher than necessary tire pressure also promotes shimmy (lower air pressure increases rolling resistance, increasing damping action). Generally, shimmy occurs on landing roll out or while taxiing, and can be stopped with light brake application. Wheel shimmy can be minimized by using the lowest practical tire pressure, having well balanced wheels and tires, and brake disks that run true and don?t drag at one point of rotation.

Personal experience: RV-4, no stiffeners, Cleveland wheel/brake assemblies and six-ply tires, no shimmy if tires at or below 24 PSI. If tires inflated to higher pressure, shimmy likely during deceleration on paved surfaces as speed decreases through approximately 15 knots.

Cheers,

Vac