Predicting Landing Gear Carbon Brake Vibration and Performance via Subscale Test and Analysis

Variation of the coefficient of friction generated in aircraft landing gear brakes can cause vibration or performance problems that damage aircraft or make control of the brake difficult. A means of detecting and predicting the range of such variation is therefore useful during the design stage of a brake. Two causes of stochastic variation, and subscale test methods to characterize the range of variation are presented. A mathematical model is developed that employs the subscale test data to represent the statistical probability of variation in full-scale brake performance. This variability is otherwise difficult to predict or detect due to the improbability of occurrence. Measured flight test brake data is compared with model predictions for two different carbon brake specimens used in full-scale carbon brake designs, and the model is shown to correlate well. An examination of the correlation, and related flight test data indicate that excessive brake torque gain caused by water desorption transition can lead to severe brake performance and vibration problems. The model in this paper enables identification of candidate brake lining materials that have a propensity for these performance problems, and allow them to be eliminated in the brake design stage. Consideration of desorption, and its probability of occurrence, offers insights to improve subscale testing, dynamometer testing, and flight-testing.