Design and analysis of semi-active landing gears for transport aircraft

Landing gears of commercial passenger transport aircraft play an increasingly important role for safety, comfort and for weight considerations. As a result and in particular for future large aircraft with take-off weights up to 600 metric tons, the contribution of the landing gears to the structural weight would become prohibitive if standard designs would simply be extrapolated. Pilot reports indicated problems caused by fuselage vibrations due to runway/landing gear excitation. This resulted in comfort loss for the passengers and for the pilots, who had difficulties to read flight displays and were therefore hampered in safely handling the aircraft. The influence of these sometimes violent oscillations on the lifetime of the airframe structure has not yet been investigated but might be substantial. These facts motivated research to investigate new concepts for advanced landing gears and to optimize their associated design parameters. The reduction of vertical accelerations of the fuselage, particularly the front section, where the most violent oscillations were found, was the primary goal of the research work. A nonlinear multibody model base was derived to simulate and optimize a semi-active nose landing gear. It is based on an existing and operating aircraft (AIRBUS A 300) and includes besides the conventional and the semi-active gear the whole elastic airframe structure and a set of different runway profiles. A multimodel multiobjective parameter optimization process was used to derive an optimal control system for the semi-active gear suitable for a wide range of ground operations. The performance of the semi-active gear was assessed by comparison with the simulated behavior of the conventional gear. Time domain as well as frequency domain analysis deduced by fast FOURIER transformation were used to evaluate the system performance. For all ground operations inspected, important improvements in the vertical acceleration of the fuselage sections were found. (orig.)Available from TIB Hannover: RN 437(96-11) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman