MAIN LANDING GEAR SHOCK ABSORBER – PRINCIPLE
OF OPERATION
In flight no load are applied to MLG (suppose the MLG retracted). The
pressure of the nitrogen balances the pressure of the hydraulic fluid in the
cylinder and maintains the separator piston in a neutral position.
The shock absorber starts to operate as soon as the helicopter touches the
ground following two subsequent phases
• first stage damping
• second stage damping
FIRST STAGE DAMPING
The first stage damping starts as the helicopter touches the ground: the
trailing arm, as a result of the impact, pulls the piston rod and moves the
separator piston.
The pressure of the oil in the chamber increases and consequently the oil is
forced to flow through the variable device orifice.
SECOND STAGE DAMPING
During the second stage damping, the displacement forces compress the
spring loaded piston which, as a consequence, opens the holes allowing the
oil to flow to the separator piston. The separator piston is pushed against the
nitrogen which gets pressurized and absorbs landing loads.
When the nitrogen has completely absorbed the landing loads, the pressure
is at its maximum and the gas starts to extend pushing the separator back to
its position forcing the oil to get back to the barrel through the holes. The
shock absorber starts retracting and the oil flows back to the barrel forcing
the spring loaded piston to return to its initial position closing the holes.