Conceptual design of a hard landing indication system using a flight parameter sensor simulation model

A Flight Parameter Sensor Simulation (FPSS) model has been developed to assess the conservatism of the landing gear loads calculated using a hard landing analysis process. Conservatism exists due to factors of safety that are added to the hard landing analysis process to account for uncertainty in the measurement of certain flight parameters. The FPSS model consists of: (1) an aircraft and landing gear dynamic model to determine the 'actual' landing gear loads during a hard landing; (2) an aircraft sensor and data acquisition model to represent the aircraft sensors and flight data recorder (FDR) systems to investigate the effect of signal processing on the flight parameters; (3) an automated hard landing analysis process, representative of that used by airframe and equipment manufacturers, to determine the 'simulated' landing gear loads. Using a technique of Bayesian sensitivity analysis, a number of flight parameters are varied in the FPSS model to gain an understanding of the sensitivity of the differencebetween 'actual' and 'simulated' loads (measured as Mean-Square Error (MSE)) to the individual flight parameters in symmetric, two-point landings. This study shows that the tyre-runway friction coefficient and aircraft vertical descent velocity (Vz) contributed the most to the spin-up and spring-back drag axle response load MSE and bending moment MSE. It was also found that aircraft vertical descent velocity, mass, centre of gravity position and tyre type had significant influences on the maximum vertical reaction vertical axle response load MSE. Due to the modelling technique, it was also found that vertical acceleration was as significant as Vz in reducing the MSE. While ground speed and aircraft pitch did not change considerably from the 'actual' to the 'simulated' landings, their interactions with tyre-runway friction coefficient and aircraft vertical descent velocity contributed to the MSE in all cases. Of equal importance, it was also shown that within the range studied, shock absorber servicing state and tyre pressure do not contribute significantly to the MSE and learning the true value of these flight parameters would not reduce the MSE.