What is shimmy on landing gear and how is it controlled?

• A. Shimmy is lateral oscillation of the wheel assembly due to dynamic instability; controlled by shimmy dampers, friction dampers, and proper nose wheel alignment and tire condition.
• B. Shimmy is vertical vibration of landing gear.
• C. Shimmy is a type of wheel wear.
• D. Shimmy is a flight control input.

Answer: (A)

Shimmy is lateral oscillation of the landing gear wheel assembly, driven by dynamic instability between the wheel, tire, and steering linkage as the gear moves. In flight, taxi, or after touchdown, the wheel and its axle act like a pendulum with steering forces, and if energy isn’t damped quickly enough, a small disturbance can grow into a rapid side-to-side wiggle. This motion is centered in the wheel assembly and is distinct from vertical gear vibration or simple tire wear.

The best way to control shimmy is to damp it out with dedicated damping devices and to reduce the factors that excite it. Shimmy dampers, which can be hydraulic or friction-based, absorb energy from the lateral motion and restore stability, preventing the oscillation from growing. Proper nose-wheel alignment and tire condition also play crucial roles: correct alignment minimizes unwanted steering input and toe-in/out variations that can feed the oscillation, while good tire condition (uniform roundness, proper inflation, and even wear) ensures consistent contact forces and reduces the tendency to shimmy. Regular checks of the gear joints, lubrication, and anti-shimmy devices help keep the system stable.

Shimmy is not vertical gear vibration, nor a wear issue, nor a flight-control input. It’s specifically about lateral motion of the wheel assembly and how damping and proper fitment keep that motion from becoming unstable.