Semi-levered landing gear and auxiliary strut thereof

Abstract

A semi-levered landing gear includes a main strut, a wheel truck pivotally attached at a main pivot to a lower end of the main strut and supporting forward and aft wheels, and an auxiliary strut attached at its upper end to the main strut and at its lower end to the wheel truck forward of the main pivot. The auxiliary strut includes a main piston that slides within a cylinder barrel and is attached at its lower end to the auxiliary pivot, and a floating piston that slides relative to the cylinder barrel and the main piston and divides the cylinder barrel into a pair of fluid chambers. The main piston includes snubbing holes or orifices through which fluid can flow between the two fluid chambers. The auxiliary strut also includes a lock-up valve that slides relative to the floating and main pistons and is configured to close the fluid path through the snubbing holes or orifices when the main and floating pistons are in predetermined positions relative to the lock-up valve, thereby locking the strut at a predetermined fixed length. The lock-up valve is configured such that the strut locks up at an intermediate length between a minimum and a maximum length of the strut, so that on takeoff, as the main strut extends, the auxiliary strut locks up to cause the wheel truck to tilt into a nose-up attitude. In one embodiment, the lock-up valve is actuatable to move into either a retracted position providing a short extension before locking up, or an extended position enabling the auxiliary strut to extend a greater amount before locking up. The auxiliary strut is also actuatable to extend the main piston for stowing the landing gear and to retract the main piston for tilting the wheel truck on landing approach.