NONLINEAR MODEL FOR AIRCRAFT BRAKE SQUEAL ANALYSIS - STABILITY ANALYSIS AND PARAMETRIC STUDIES

Results are presented from analyses of primary squeal-mode vibration i n aircraft brake systems. System stability is investigated by determin ing the eigenvalues of linearized perturbation equations at each stead y-state operating point of the nonlinear system. Time-history response s are obtained by integrating the complete set of nonlinear dynamic eq uations. Results are given from analyses conducted using two versions of the nonlinear squeal model, a single-wheel model representing a typ ical dynamometer configuration, and a fore-aft wheel pair model repres enting one side of a main landing-gear truck. In general, the model pr edicts system instability at low braking pressures and stability at hi gh braking pressures. The effects on stability of variations in brake pressure, friction coefficient, and torsional stiffness are shown. The nonlinear squeal model indicates that system instability can occur wi th a constant friction coefficient and that system stability decreases with increasing brake-friction coefficient. It is shown that proper s election of brake heat stack mechanical properties and design geometry can produce a stable system. Results indicate that a fore-aft brake p air will be more unstable than a single brake, which is in agreement w ith dynamometer and airplane test data.