Realistic Evaluation of Airplane Brake Vibration by Laboratory Test and Analysis

Abstract An important part of the design of airplane brakes is the laboratory verification of their capability to absorb the kinetic energy of the airplane under various operating conditions ranging from normal service energy levels to the very high energy of a rejected takeoff (RTO). These “stops”, as dynamometer brake applications are called, must demonstrate acceptable temperature levels for the wheel and tire, the ability of the brake to carry out numerous taxi and service type stops without any servicing, and acceptable wear rates for the friction material so as to make the brake economically feasible for use by the airlines. These laboratory tests are typically carried out on an adjustable inertia roadwheel dynamometer. The wheel and tire are “landed” against the flywheel of the dynamometer until the correct radial load is developed on the tire. The brakes are then applied to decelerate the dynamometer to a low taxi speed or stop it completely. With such a system various spectrums of landing and multiple taxi stops can be programmed to yield a simulation of actual airplane operation. An attempt has been made to extend this type of dynamometer testing to examine the vibrational characteristics of the brake as part of the total landing gear system, in addition to its performance as an energy absorber. Since these total-system vibrations can be destructive to both the brake and the landing gear structure, this type of vibrational evaluation is as important as the energy evaluation of the brake. For many transport aircraft, particularly those with four or more wheels per landing gear, it is impossible to incorporate the entire landing gear into the dynamometer testing. The nature of the testing extension has therefore been to simulate the behavior of the gear with simpler devices called simulators. In order to duplicate as nearly as possible the vibrational characteristics that will be experienced on the airplane, various types of landing gear simulators have been used in conjunction with dynamometer testing. This paper discusses the pros and cons of landing gear simulators and a proposed approach that would utilize the simulator in a program to more accurately predict actual airplane landing gear vibrational characteristics.