Continuation analysis of landing gear mechanisms

• Main Author: Knowles, James
• Published: University of Bristol 2012
• Subjects: 621.134381
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.570854

Current landing gear mechanism analysis methods focus on determining purely geometric behaviour of the retraction mechanism, to ensure that the landing gear will meet its stowed constraints. For detailed analysis work, dynamic simulation is the standard method to determine underlying causes of nonlinear behaviour. The work presented in this thesis provides an alternative analysis approach for analysing quasi-static landing gear mechanisms, to be used to complement and inform the use of dynamic simulations. This alternative method of investigating quasi-static mechanisms is first presented for two planar mechanism example cases: an overcentre mechanism and a nose landing gear mechanism. The method uses static equilibrium equations along with equations describing the geometric constraints in the mechanism. In the spirit of bifurcation analysis, solutions to these steady-state equations are then continued numerically in parameters of interest. Results obtained from the numerical continuation agree with the equivalent results obtained from two overcentre mechanism dynamic models, whilst offering a considerable computation time reduction. The analysis performed with the nose landing gear model demonstrates the flexibility of the continuation approach, allowing conventional model states to be used as continuation parameters without a need to reformulate the equations within the model. The modelling approach is then demonstrated for the case of non-planar landing gear mechanisms, with application to a three-dimensional aircraft main landing gear mechanism model. A design case-study is performed on the landing gear actuator position to demonstrate the potential industrial relevance of the method. The trade-off between maximal efficiency and peak actuator force reduction when positioning the actuator is investigated. The problem formulation allows actuator force, length and efficiency information to be obtained from a single numerical continuation run with minimal data post-processing. Finally, a model of a dual sidestay landing gear mechanism is, presented and used to investigate the mechanism downlock sensitivity to attachment point deflections. Motivation for this study is provided by a desire to understand the underlying nonlinear behaviour that may prevent a dual sidestay landing gear from down- locking under certain conditions. An investigation into the effect of sidestay angle reveals that the geometry prevents the gear from fully retracting at certain sidestay angles. Sidestay flexi- bilities are then introduced to enable the downlock loads to be investigated. It is demonstrated that deflections of even a few milimetres can provide a force barrier to the landing gear down- locking. The underlying nonlinear behaviour is attributed to the formation of double hysteresis loop in the force-locklink angle plane.