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Parts & Functions of Retractable Wing Gear


1. JURY STRUTS – side struts are held in place by this component in which also folds out when the gear is lowered.

2. SHIMY DAMPER – It controls nose wheel shimmy through hydraulic damping.

3. WHEEL WELL – a recessed compartment on the underside of an airplane for the reception of a wheel of a retractable landing gear.

4. CASTORING – Ability of the nose wheel to turn to either side in response to the result of differential braking or forces on the rudder.

5. TORQUE LINKS – Rotary movement of the inner cylinder is stopped and up and down movement is limited by this component.

6. SIDE STRUT – It supports the leg laterally during crosswind landings, take-offs, and taxiing.

7. TILLER – The nose wheel can be steered both by using the rudder pedals or the TILLER.

8. TRUNNION – The leg is attached to the wing spars by this component on which the leg is free to rotate laterally.

9. RUBBER CORD – A landing gear shock absorption system wherein the landing force is directed against a number of turns to form a grommet/loop

10. SEPARATOR PISTON – The fluid and gas inside the oleo-pneumatic strut are kept apart by this.

11. FLUTTER VALVE – It limits the rate of movement of the landing gear strut when it is extending or contracting.

12. HYDRAULIC FLUID – It consists the upper cylinder of the oleo-pneumatic strut & dampen

oscillations of the pistons.

13. LANDING GEAR – It is the undercarriage of an aircraft and may be used for either takeoff or landing.

14. SHIMMY – It is a rapid, sinusoidal oscillation or vibration into the nose undercarriage unit.

15. HYDRAULIC SYSTEM – It normally provides the operating power for retractable landing gears.

16. TAILDRAGGER – A landing gear layout that has a tail wheel behind the main wheels.

17. AXLE – A bar connected to the center of the wheel that allows it to turn.

18. TRICYCLE – Most aircraft use this type of layout wherein the two main undercarriage units are positioned just aft of the aircraft’s CG.

19. SPRING STEEL LEG – A type of fixed landing gear shock absorption system usually employed at the main undercarriage positions.

20. GAS – It supports the aircraft on the ground & cushions bumps during taxiing and absorbs shock on landing.

21. MECHANICAL LOCK – Safety devices that are intended to prevent inadvertent retraction of landing gears when the aircraft is on the ground.

22. TORSION – A type of load sustained by the landing gear during ground maneuvering.

23. STRUT – An aircraft component designed to resist compressive forces.

24. TOWIING – The forward movement of an aircraft using the power of a specialized ground vehicle attached to or supporting the NLG.

25. DRAG STRUT – It supports the leg in a fore and aft direction and rearward bending loads during braking.

Parts & Functions of Retractable Wing Gear


TRUNNION – The leg is attached to the wing spars by a cylindrical beam by this component on which the leg is free to rotate laterally.

STRUT OUTER CYLINDER – The upper part of the legs forms the outer cylinder or the oleo pneumatic strut.

STRUT INNER CLYLINDER – Is connected to the wheel boogie or truck beam.

The truck beam can pivot in its central point in a controlled way. This allows all main wheels to be on the ground with the fuselage in the take-off or landing attitude.

WHEELS – There are axles connected to a pair of brake wheels at each end of the truck beam.

UPPER AND LOWER TORQUE LINKS – Prevent rotation between the shock strut inner and outer cylinders without affecting their reciprocating action during normal operation of the strut.

DRAG STRUT – Supports the leg in a fore-and-aft direction.

UPPER AND LOWER SIDE STRUT – Supports the leg laterally. They fold out when the gear is lowered and are then held in place by the JURY STRUT.

JURY STRUT – Folds out during extension. It is pulled over center by the DOWN LOCK ACTUATOR geometrically locking the gear down (DOWNLOCK ACTUATOR).

  • Side struts are held in place by this component in which also folds out when the gear is lowered.

SPRING – If the gear is lowered without hydraulic power, then the over centering action will be performed by an internal spring in the DOWN LOCK ACTUATOR.


Parts & Functions of Retractable Wing Gear

The thread of the tire is situated in the CROWN and SHOULDER section.

[TREAD – rubber is plain and smooth or molded on a block pattern (diamonds)]

SIDEWALL – allows the tire to be flexible

BEAD – seated inside the flange of the wheel


      • Provides storage space for the system fluid and sufficient air space
      • Prevent over pressurization
      • Delivers and receives oil from the actuator
      • It provides a head of fluid for the pump
      • To supply fluid at a constant rate
      • Draw oil from the reservoir and deliver a supply of fluid to the system
    • PURPOSE 
      • Keep the fluid clean during use
      • Removes foreign particles from the fluid
      • Safety device to relieve excess pressure
      • Return fluid to the reservoir
      • Some are adjusted to blow off at a pressure slightly higher than normal system pressure (Thermal relief valve)
      • Direct fluid to the appropriate side of an actuator
      • Controls the direction, pressure, and flow rate of a fluid flowing through the circuit
      • Provides a passageway to direct fluid. It also acts as a return path for the oil to the reservoir.
      • To dampen out pressure fluctuations
      • Store hydraulic fluid under pressure
      • Provides small emergency supply of fluid when the pump failed
      • Allows thermal expansion and contraction of fluid trapped in the pipes


The pump circulates the fluid from the reservoir to the pressure filter to remove foreign particles in the fluid if there is any through the selector valves. In this arrangement, the system pressure line goes through each selector valve. Fluid is always allowed free passage through each selector valve and back to the reservoir until one of the selector valves is positioned to operate a mechanism.

When one of the selector valves is positioned to operate an actuating device, fluid is directed from the pump through one of the working lines to the actuator. With the selector valve in this position, the fluid flow through the valve to the reservoir is blocked. The pressure builds up in the system to overcome the resistance and moves the piston of the actuating cylinder; fluid from the opposite end of the actuator returns to the selector valve and flows back to the reservoir. The relief valve will relieve excess pressure if the selector is not returned to its neutral position before the fluid is directed back to the reservoir.

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