Influence of Variable Side-Stay Geometry on the Shimmy Dynamics of an Aircraft Dual-Wheel Main Landing Gear

Abstract

General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. Full terms of use are available: http://www.bristol.ac.uk/pure/about/ebr-terms Copyright © by SIAM. Unauthorized reproduction of this article is prohibited. Abstract.Commercial aircraft are designed to fly but also need to operate safely and efficiently as vehicles on the ground. During taxiing, take-off, and landing the landing gear must operate reliably over a wide range of forward velocities and vertical loads. Specifically, it must maintain straight rolling under a wide variety of operating conditions. It is well known, however, that under certain conditions the wheels of the landing gear may display unwanted oscillations, referred to as shimmy oscillations, during ground maneuvers. Such oscillations are highly unwanted from a safety and a ride-comfort perspective. In this paper we conduct a study into the occurrence of shimmy oscillations in a main landing gear (MLG) of a typical midsize passenger aircraft. Such a gear is characterized by a main strut attached to the wing spar with a side-stay that connects the main strut to an attachment point closer to the fuselage center line. Nonlinear equations of motion are developed for the specific case of a two-wheeled MLG configuration and allow for large angle deflections within the geometrical framework of the system. The dynamics of the MLG are expressed in terms of three degrees of freedom: torsional motion, in-plane motion, and out-of-plane motion (with respect to the side-stay plane). These are modeled by oscillators that are coupled directly through the geometric configuration of the system as well as through the tire/ground interface, which is modeled here by the von Schlippe stretched string approximation of the tire dynamics. The mathematical model is fully parameterized and parameters are chosen to represent a generic (rather than a specific) landing gear. In particular, the positions of the attachment points are fully parameterized so that any orientation of the side-stay plane can be considered. The occurrence of shimmy oscillations is studied by means of a two-parameter bifurcation analysis of the system in terms of the forward velocity of the aircraft and the vertical force acting on the gear. 1. Introduction. The technical term shimmy is generally used to describe the self-sustained oscillations of a system with one or more rolling wheels and represents a relatively well-studied problem in engineering. Typical examples of shimmy with which the reader may be familiar range from the weaving of a towed trailer at high speeds to the sudden oscillation of a loose trolley wheel. The phenomenon first began to attract research interest in connection with the undesirable oscillation of the steering mechanism of early automobiles. These vehicles shared the common design elements of a single front axle rigidly connected to the front wheels, and the severity of the problem increased further with the development...

Effects of Freeplay on Dynamic Stability of an Aircraft Main Landing Gear

“…In addition to the torsional, lateral and longitudinal motion allowed previously 4 and expressed by the angles ψ, δ and β, we extend our model to include compression of the main strut. This motion is represented by the addition of an axial degree of freedom expressed by the variable η.…”

“…2 Our focus here is on main landing gear (MLG) shimmy. 3 In a previous study 4 we used a nonlinear model with three DoFs to express the dynamics of a MLG of dual-wheel configuration, using numerical continuation methods to study the onset of shimmy oscillations. This model allowed for a single side-stay of arbitrary orientation and we found its positioning to be highly influential on the complexity of the behaviour observed, owing to additional geometric coupling between the different oscillatory DoFs.…”

Optimization of a Main Landing Gear Locking Mechanism Using Bifurcation Analysis

“…Bifurcation analysis and numerical continuation method have been widely applied to aircraft dynamics analysis for many years, as discussed in the review by Sharma et al [13]. For example, landing gear shimmy oscillations have been studied to identify regions in which the only stable steady-state solution is that where these is no shimmy motion and their boundaries with regions where shimmy exists considering two key parameters: the forward velocity of aircraft and the vertical force acting on the landing gear [14][15][16]. Similarly, the characterization of aircraft ground handling behaviors has been studied using bifurcation analysis method.…”

Modeling of shimmy oscillations in aircraft landing gear

“…The developed models of shimmy oscillations are mainly based on different number of degrees of freedom, different analysis methods and different ways of modelling the elastic tyres [8][9][10][11][12][13][14]. These models allow for the analysis of the stability and the response of shimmy oscillations.…”