Implications of simultaneous freeplay on limit cycle oscillations of aeroelastic system with aileron and trim-tab

Abstract

Nonlinear effects can change substantially the dynamics of a flight. Friction and freeplay in control surfaces can also imply to change the stability of aerial vehicles or limitations in the operational flight envelope. In this context, this research comprises an investigation of the dynamics of Limit Cycle Oscillations (LCO) due to simultaneous freeplay on aileron and trim-tab. The influence of friction is considered too. The proposal comprises to apply three methods to predict LCO amplitudes and frequencies: harmonic balance method (or describing functions) combined with the equivalent linearization technique; numerical continuation; and normal form method. For the three approaches, adaptations and developments will be made to consider the nonlinear friction and double freeplay. It will be considered a four degrees of freedom aeroelastic system and unsteady aerodynamic forces written in the time domain though rational function approximations to establish a state space representation. An extended Hénon's technique will be developed to integrate in time the nonlinear equations of motion. It will be discussed the implications of simultaneous freeplay, combined with friction, on the LCO also using bifurcations diagrams to analysis the aeroelastic stability. (AU)