Aircraft Landing Gear Systems

Landing Gear Systems

• Landing gear designs vary from fixed arrangements to complex retractable systems.

Landing Gear Configurations

• Aircraft landing gear can be classified as either tricycle or conventional.
• Conventional geared aircraft:
  • Have two main wheel assemblies and a tail wheel.
  • Are suitable for rough field operations and associated with older aircraft.
  • Advantages:
    • Reduced drag in the air.
    • Reduced landing gear weight.
  • Disadvantages:
    • Less stable on the ground.
    • Require more skill when taxiing, during takeoff and landing.

Tricycle Landing Gear

• Have a nose wheel assembly and two main gear assemblies.
• Allow the aircraft fuselage to be in a level attitude on the ground.
• Advantages:
  • Cabin area is level, making it easy for passengers to move inside the aircraft.
  • Stable on the ground.
  • Easy to control when taxiing, during takeoff and landing.

Classification of Landing Gear

• Main landing gear:
  • Supports the airplane on land or water.
  • Components:
    • Wheels, floats, or skis.
    • Shock absorbing equipment.
    • Brakes.
    • Retracting mechanism.
    • Control and warning devices.
    • Cowling and fairing.
    • Structural members for attachment to the primary structure of the airplane.
• Auxiliary landing gear:
  • Tail or nose wheel installations.
  • Skids.
  • Outboard pontoons.
  • Cowling and reinforcements.

Types of Landing Gear

• Non-absorbing landing gear:
  • Rigid landing gear (used in helicopters and sailplanes).
  • Shock-cord landing gear (uses rubber shock cords).
  • Spring-type gear (uses single, tapered strips or tubes of spring steel or composite material).
• Shock-absorbing landing gear:
  • Spring-oleo struts (piston and coiled spring).
  • Air-oleo (principle operation is similar to spring-oleo struts).

Fixed Gear

• Non-retractable landing gear attached to structural members of the airplane.
• Often equipped with fairing to reduce drag.
• Wheel pants are used to cover the wheel and tire to reduce drag.
• Usually found on small aircraft.

Retractable Landing Gear

• Developed to eliminate drag caused by exposure of landing gear to airflow during flight.
• Retraction is accomplished with hydraulic or electric power.
• In emergency, backup hydraulic systems, stored air or gas can be directed into actuating cylinders.
• Much more complex, with primary importance in the safe operation of the aircraft.

Landing Gear Components

• Components of landing gear assemblies:
  • Trunnion (attached to the airframe).
  • Struts (vertical member of the landing gear assembly).
  • Torque links (connects strut cylinder to piston and axle).
  • Truck (located on the bottom of the strut piston).
  • Drag link (stabilizes the landing gear assembly longitudinally).
  • Side brace link (stabilizes the landing gear assembly laterally).
  • Overcenter link (applies pressure to the center pivot joint).
  • Swivel gland (used in retractable landing gear).
  • Shimmy dampers (used to reduce shimmy).

Tires and Wheels

• Types of tires:
  • Type I (smooth contour, no longer active, used on fixed gear aircraft).
  • Type II (high pressure, not applicable).
  • Type III (low pressure, common general aviation tire).
  • Type IV (extra low pressure, not applicable).
  • Type V (not applicable).
  • Type VI (low profile, not applicable).
  • Type VII (extra high pressure, low speed, and extra high pressure, high speed).
  • Type VIII (extra high pressure, low profile, low speed, and extra high pressure, low profile, high speed).