Recent Developments at the Numerical Simulation of Landing Gear Dynamics

Aircraft landing gears support the aircraft during ground operations, including take-off, landing impact, taxiing, gate handling and maintenance. Mostly for reasons of minimum mass and ground clearance, landing gears are slender structures which exhibit a considerable dynamic response to ground load excitations. As the landing gear is one of the few systems on the aircraft without redundancies, the knowledge of landing gear dynamics is crucial for aircraft design and aircraft safety. Simulation of landing gear dynamics is a cornerstone of aircraft loads analysis, as well for vertical loads resulting from touch-down as for longitudinal and lateral loads resulting from braking, steering and towing. Another important field of interest is landing gear vibrations like gear walk and shimmy. Those phenomena can be brake induced or result from tire spin-up at touchdown or simply from a coupling of dynamics of the running tire and structural mechanics of the landing gear leg. All those effects strongly depend on a number of parameters such as aircraft speed, landing gear vertical deflection, tire pressure and wear of the parts. Many of those parameters can only be estimated and might change during the operation of the aircraft. Numerical investigation is thus a challenging task. Analysis methods exist both in the frequency domain and in the time domain. As stability analysis is straight forward in frequency domain methods, this approach is still often used. However, in many cases nonlinearities are dominant which lead to limit-cycle characteristics of the vibrations. Here, multibody modelling or a mixture of multibody and finite element modelling including time domain simulation is used. In the article, a general outline is given of how vibration problems in landing gears can be treated by numerical analysis methods. The article will start with a classification of typical problems, give a short overview of classical papers, and explain typical approaches. In addition, alternative approaches for stability analysis and for the detection of limit-cycle oscillations as well as state-of-the-art modelling approaches will be presented.