Simulation of Landing Gear Dynamics and Brake-Gear Interaction

Abstract

The term landing gear indicates one of the main functions of the gear, namely the containment of the landing gear impact but it fails to describe the other functions, such as provision of means for the aircraft to maneuver on the ground, taxi and take off. Landing gear dynamics, especially shimmy and brake-induced vibrations, is one of the problems faced today by the aircraft community. Landing gear vibrations may lead to fatal accidents due to excessive wear, it can also shorten the gear life, and affect comfort to the pilot and passengers. Among the most important reasons for landing gear vibrations are unsuitable combination of structural stiffness, damping, and pneumatic tire characteristics further more an unlucky combination of brake system design with the tire physics can produce a serious vibration problem. Shimmy may be caused by a number of conditions such as low torsional stiffness, excessive free play in the gear, wheel imbalance, or worn parts. 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. 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 ground maneuvers. 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 important parameters that may affect the stability and comfort. A multi-body simulation (MBS) model of a landing gear was prepared using Nastran for this purpose and imported into the MBS tool SIMPACK. An adequate modeling of tire and brake dynamics is an important issue for the analysis of the behaviour of an aircraft during ground maneuvers as potentially unstable phenomenon such as gear walk and shimmy may occur in these phases and was also implemented into the MBS tool. With the help of all these modules different ground maneuvers were simulated including braked maneuver. Effect of various parameters on landing gear vibrations was also studied. Finer points are highlighted in the conclusion which may require more detailed study and analysis.