Chapter 29: Landing Gear Systems
29.1 Purpose and Components
- The landing gear supports the aircraft on the ground, absorbs landing shocks, and allows for
- taxiing and steering.
- Oleo-Pneumatic Strut: The most common type of shock absorber. It consists of a cylinder
- containing both hydraulic fluid and compressed nitrogen gas.
- During compression (landing), the fluid is forced through a small orifice, which damps the
- impact.
- The compressed nitrogen acts as a spring, supporting the aircraft's weight and re-extending
- the strut.
- Torque Links (Scissors): A hinged link that connects the inner and outer cylinders of the
- strut, allowing it to compress while preventing it from rotating.
- Nose Wheel Steering: Allows the pilot to steer the aircraft on the ground using tiller wheels
- r rudder pedals.
- Shimmy Damper: A small hydraulic damper on the nose gear that prevents rapid, unstable
- scillations (shimmy) of the nose wheel during takeoff and landing.
29.2 Retraction Systems
- Operation: Retractable landing gear systems are typically operated hydraulically. When the
- gear is selected UP, hydraulic pressure is directed to actuators that retract the gear into wheel
- wells, which are then covered by doors to maintain aerodynamics.
- Locks: Up-locks and down-locks are mechanical locks that ensure the gear is held securely
- in the extended or retracted position.
- Safety Devices:
- A selector lock prevents the gear lever from being moved to the UP position while the
- aircraft is on the ground. This is controlled by weight-on-wheels switches (also known as
- squat switches or an air/ground logic system).
- Ground locks (safety pins with red flags) are inserted manually on the ground to prevent
- accidental gear retraction.
- Emergency Extension: In case of a hydraulic failure, an emergency system allows the gear
- to be lowered. This often involves mechanically releasing the up-locks and allowing the gear
- to free-fall into the down-and-locked position due to gravity and air loads.