Simulation of Landing Gear Dynamics Using Flexible Multi-Body Methods

Abstract

The predominant task of an airplane is no doubt to fly with the best performance achievable. It must not be forgotten, however, that it will spend a good part of its life on the ground. Landing gear dynamics, especially shimmy and brake-induced vibrations, is one of the problems faced today by the aircraft community. Though they are not catastrophic, they can lead to fatal accidents due to excessive wear. It can also shorten the gear life and cause discomfort to the pilot and passengers. Although equations for representing various parts of a landing gear are well established, solving the problems manually with mathematical programs can be slow and laborious. Simplifications made to reduce problem size may introduce inaccuracies such that a design modification to correct a problem in one area causes unforeseen vibrations in other parts of the structure. In many cases, vibration problems may not be uncovered until physical prototypes are built and tested, adding considerable time and expense to the product development cycle. However, many commercially available computer-aided engineering tools have made it possible to test some of the problems in the design phase by simulating the landing gear impact and rolling. An adequate modeling of tire and brake dynamics is an important issue for the analysis of the behavior of an aircraft during ground maneuvers as potentially unstable phenomena such as gear walk and shimmy may occur in these phases. At the German Aerospace Center (DLR), simulation of such an unstable and complex phenomenon during aircraft ground maneuvers is done to detect vibrations in aircraft landing gear and study the effect of brake dynamics and other important parameters that may affect the stability and comfort.