Bifurcation Characteristics of Emergency Extension of a Landing Gear Mechanism Considering Aerodynamic Effect

The emergency extension system for nose landing gear (NLG) is vitally important for safe landing in the event of hydraulic source failure. To study the dynamic properties of NLG emergency extension, it is necessary to explore the aerodynamic load in detail, which is a potential adverse factor that hinders the successful deployment of NLG. The emergency extension failure of a door-linkage NLG mechanism was studied from a novel bifurcation perspective in this paper. NLG models (excluding and including aerodynamic loads) formulating the mechanism as a series of steady-state constraint equations were derived. Solutions to these equations were continued numerically, and the NLG retraction-extension cycles in different models were compared. The critical condition for smooth extension was obtained based on the bifurcation analysis. The failure principle was explained, that is, the disappearance of bifurcation points characterizing the successful locking. The variations of bifurcation point as a function of spring parameters and door aerodynamic loads were investigated. An effective solution to the failure was put forward in which the unlocking force is reduced by 33.0%.