High fidelity landing gear modeling for real-time simulation

The paper presents a high fidelity landing gear model for real-time simulation implemented in MATLAB/SIMULINK. The gear is assembled from strut elements connected with rotary joints, allowing the representation of any landing gear configuration and geometry as a chain of these basic elements. Every base element features two degrees of freedom, a linear shock strut deflection and a rotary deflection. The equations of motion of the gear elements are coupled with the aircraft rigid body dynamics. They have been derived using the Newton-Euler method for multi body systems according to the principle of Jourdain which postulates that the virtual performance of constraint forces and moments vanishes. The masses of the gear elements are considered rigid bodies with individual inertia tensors. To remain technically correct, the equations are based on the same inertial frame as that used for the aircraft motion, an earth-centered inertial frame. The contact point of each of the tires is computed based on actual tire shapes and not on infinitesimally thin discs. Normal tire forces are computed as nonlinear spring and damper forces depending on the distance of the center of rotation of the tire from the contact point with the ground and the rate of change of this distance respectively. Axial and lateral Friction as well as braking forces and moments can be computed from different tire models.