Abstract: For the case in which the rigid mode and the first n modes of a flexible airplane are considered, the body of the airplane is defined as a multi-mass equivalent system and the calculation formulas of the parameters of the system are derived, which presents a model for testing/verifying landing impact load, landing work etc. under the influence of fuselage vibrations and also presents a simple and clear equivalent system for landing gear design analysis. The formula for calculating the landing work, displacement at the wing tip, the shears and bending moments of the wing of a flexible airplane are also given. From an overall point of view, structure deformation of airplane must be considered and optimization design must be used in landing gear design of a flexible airplane.

Key words: aircraft design, physical model, equivalent modal analysis, flexible airplane, landing gear, landing impact response