What is shimmy, and how is it mitigated in the nose wheel?

• A. Shimmy is rapid, oscillating steering of the nose wheel due to instability; mitigated by damper systems, proper tire pressures, and steering linkages.
• B. Shimmy is a type of brake fade under heavy load.
• C. Shimmy is wheel wobble during gear retraction; mitigated by lowering speed.
• D. Shimmy is gear door flutter; mitigated by lubrication.

Answer: (A)

Shimmy is rapid, self-excited side-to-side oscillation of the nose wheel steering that can occur when the nose gear, tire, and steering linkage enter a vibrating condition. This instability can be triggered by factors like braking, steering input, or runway irregularities, and it can damage components if not controlled. The best way to mitigate it is through a combination of damping and proper geometry: a nose-wheel shimmy damper absorbs energy from the oscillations and quickly slows them down, preventing the vibration from growing. Keeping tire pressures within specification ensures the tire’s dynamic stiffness and response don’t promote resonance, and correctly adjusted steering linkages (with proper lubrication and minimal play) prevent loose or binding motion that can sustain shimmy. Some designs also include anti-shimmy devices or centering mechanisms to help return the wheel to straight travel. Other options describe different issues that aren’t about nose-wheel oscillation, such as brake fade, wobble during gear retraction, or gear-door flutter.