Modeling the compression dynamics of main a landing gear strut of a helicopter

Аuthors

Zagidulin A. R.^*, Podruzhin E. G.^**

Novosibirsk State Technical University, 20, prospect Karla Marksa, Novosibirsk, 630073, Russia

*e-mail: zagidulin@corp.nstu.ru
**e-mail: planer@craft.nstu.ru

Abstract

The paper proposes a method for simulating the two-dimensional motion of an arbitrary holonomic rigid-body system. This method allows to automate the process of constructing models of aircraft landing gear legs with arbitrary kinematic schemes. It is based on the solution of the Lagrange equations of the first kind. The method allows to model equality (bilateral) and inequality (unilateral) constraints, which restrict the motion of the rigid bodies system. The ideal holonomic constraints are imposed on the positions of the bodies. These constraints are described by the following equations

where x is the position vector of the bodies of the system ; for equality (bilateral) constraints ; for inequality (unilateral) constraints; d is the number of constraints , which are imposed on the system.
The equations of system motion are written in matrix form as follows:
  where F is the vector of active forces; a is the acceleration vector; is the vector of Lagrange undetermined multipliers; J is the Jacobian matrix of the constraint vector; M is the diagonal matrix of lumped masses and moments of inertia of the rigid bodies.
The software, which was developed on the basis of the proposed method, was used to simulate the compression dynamics of the landing gear during landing impact. The main landing gear leg of the Ka-62 helicopter was chosen for modeling (Fig. 1). The model consists of the following five rigid bodies: wheel (1), lever (2), shock strut piston (3), shock strut cylinder (4), and load, which is applied to one leg (5). 

Fig. 1 The model of the main landing gear leg of the Ka-62 helicopter
Swivels a, b, c, and d and sliding joints e and g restrict two degrees of freedom. These joints are defined by two equality (bilateral) constraints. The cylinder rod stop f, which restricts one degree of freedom, is modeled by one inequality (unilateral) constraint. Thus the model includes a total of 13 constraints. The model also includes three forces, which act on the system: the tire-compression force P_T, the axial force in the strut shock absorber P_sh.a. and the lifting force P_L.
Figure 2 shows the calculated dependence of the force, which acts on the piston of the shock strut absorber, on the compression of the shock strut absorber as well as the diagram of the polytropic compression of gas in the first chamber of the shock strut absorber.

Fig. 2 Diagram of the axial force, which acts on the shock strut absorber, and polytropic compression of gas depending on piston stroke

Keywords:

Modeling the compression dynamics of main a landing gear strut of a helicopter

Keywords:

helicopter landing gear, oleo-pneumatic shock strut absorber, shock-absorption model, method of Lagrange undetermined multipliers

References

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