DYNAMIC ANALYSIS OF 3D LANDING GEAR MODEL WITH POSSIBLE FLAW

Aircraft landing gear is considered one of the most critical systems for at least two reasons, i.e. operational safety and that of carried people and cargo. Great instantaneous forces arise in structural components of the landing gear during the touchdown. These forces need to absorb and dissipate the energy of fall. The aeroplane designed and operated according to aeronautical standards, nowadays in force, should in a safe way absorb the portion of energy due to the aircraft fall while on landing, and that of energy generated due to the horizontal movement on the surface. The greatest loads that affect the landing gear result from either the absorption of vertical-fall energy. Proper selection/adjustment of landing-gear characteristics is a very intrinsic issue [2-5]. However, properly adjusted characteristics enable minimisation of loads that occur in the landing-gear components at the moment of touchdown. Therefore, dynamic analyses of the landing gear are conducted to provide capabilities to forecast their behaviour under hazardous conditions. This kind of investigation with numerical methods applied is much easier and less expensive than stand tests. The FEM model of the main landing gear has been developed using four types of finite elements, i.e. hexagonal elements, tetragonal elements, shell elements and rod elements to describe the damping system located in the cylinder. To describe material properties of all mechanical components (such as: the piston body, the piston cylinder, the pilot sleeve, pins, the connecting rod, wheel rim and suspension arm), a materials chart describing parameters for the elastic-plastic range was used. The surface-type contact was defined between all mating components of the landing gear. One of the most fundamental problems faced in the course of studies was how to describe behaviour of the damping system located in the landing-gear strut. To do this, a mathematical finite element was implemented. These element enable, by means of suitably verified mathematical equation, description of how an actual oleo-gas damper affects the landing gear under landing conditions. In the developed numerical model of the landing gear account was taken also of the support-wheel-related subassembly, which includes such elements as: the wheel pin, the wheel rim, and the tyre. All parts of this subassembly,