Shimmy is an oscillation in aircraft landing gear that can occur both on landing and take-off, typically in a band of velocities. It causes excessive wear on components and can cause accidents. The nose wheel is roughly like a caster on a shopping trolley: the horizontal axle of the wheel is mounted in an assembly that is free to rotate about a vertical axis. Shimmy is (or at least includes) oscillation of the wheel assembly about this vertical axis. The current engineering approach has little understanding of the physical mechanisms causing shimmy, but relies on the use of shimmy dampers, and on systematic maintenance and replacement of landing gear components.

Traditional shimmy analysis considers the effect to be linear. The Study Group considered a simplified nonlinear model for shimmy, and studied both its linear stability and its nonlinear behaviour numerically. These results are broadly in agreement with observations of shimmy in some circumstances, but a more complex model would be needed to cover effects that are neglected here.

Problem presented by
Etienne Coetzee, Airbus

Study Group contributors
Maria Aguareles (Universitat Politècnica de Catalunya)
Sergei Anisov (Utrecht University)
Mahboubeh Asgari (UCL)
David Barton (University of Bristol)
Sunny Chiu-Webster (University of Cambridge)
Giles Hunt (University of Bath)
Joanna Mason (University of Bristol)
David Parker (University of Edinburgh)
David Rodrigues (University of Bristol)
Juan Sola-Morales (Universitat Politècnica de Catalunya)
Dominic Vella (University of Cambridge)
David Wood (University of Warwick)