This paper investigates the unlocking of a
non-conventional nose landing gear mechanism that
uses a single lock to fix the landing gear in both its
downlocked and uplocked states (as opposed to having two separate locks as in most present nose landing gears in operation today). More specifically, we
present a bifurcation analysis of a parameterized mathematical model for this mechanical system that features elastic constraints and takes into account internal
and external forces. This formulation makes it possible to employ numerical continuation techniques to
determine the robustness of the proposed unlocking
strategy with respect to changing aircraft attitude. In
this way, we identify as a function of several parameters the steady-state solutions of the system, as well as
their bifurcations: fold bifurcations where two steady
states coalesce, cusp points on curves of fold bifurcations, and a swallowtail bifurcation that generates
two cusp points. Our results are presented as surfaces
of steady states, joined by curves of fold bifurcations,
over the plane of retraction actuator force and unlock
actuator force, where we consider four scenarios of the
aircraft: level flight; steep climb; steep descent; intermediate descent. A crucial cusp point is found to exist irrespective of aircraft attitude: it corresponds to the
mechanism being at overcentre, which is a position
that creates a mechanical singularity with respect to
the effect of forces applied by the actuators. Furthermore, two cusps on a key fold locus are unfolded in a
(codimension-three) swallowtail bifurcation as the aircraft attitude is changed: physical factors that create
these bifurcations are presented. A practical outcome
of this research is the realization that the design of this
and other types of landing gear mechanism should be
undertaken by considering the effects of forces over
considerable ranges, with a special focus on the overcentre position, to ensure a smooth retraction occurs.
More generally, continuation methods are shown to
be a valuable tool for determining the overall geometric structure of steady states of mechanisms subject to
(external) forces.
History
School
Aeronautical, Automotive, Chemical and Materials Engineering
This is an Open Access Article. It is published by Springer under the Creative Commons Attribution 4.0 Unported Licence (CC BY). Full details of this licence are available at: http://creativecommons.org/licenses/by/4.0/