Aircraft Landing Gear: Types and Functions

Landing Gear Purpose

• The primary purpose is to absorb shock during landing and allow for ground steering.

Landing Gear Types

• The first type of landing gear was skis used on the Wright Flyer.
• The first aircraft with wheels used a tricycle landing gear configuration.
• Tricycle gear consists of a main wheel pair behind the Center of Gravity (CG) and an auxiliary wheel under the nose.
• Tricycle gear replaced Tailwheel landing gear, which had become popular as engine technology allowed for powerful radial engines and large propellers that required a greater distance between prop and ground.

Tailwheel Configuration

• Tailwheel configuration is considered "conventional gear"
• Rudder pedals are connected to the tailwheel via cables and springs.
• Tailwheel is fully castering, locking in position for takeoff and unlocking in position for landing.
• Requires independent braking to steer.

Nose Wheel Configuration

• Most popular type.
• Nose wheel connected to rudder for steering.
• Some large aircraft utilize hydraulics for steering.
• Some have independent steering wheels or yokes for ground maneuvering.

Main Wheels

• Number and location vary depending on aircraft type.
• Some main gear have two wheels.
• Multiple wheels spread weight over a larger surface.
• Multiple wheels provide a safety margin if a tire fails.
• Heavier aircraft may have 4 or more wheels.
• A "boggie" or "truck" mechanism is used to attach multiple wheels to a single strut.

Tandem Wheel Configuration

• Main gear is in line down the center of the fuselage.
• Examples include Gliders and Harrier jets.
• Uses outrigger wheels to support the wings.

Skids

• Primarily found on helicopters.
• Has been used on fixed-wing aircrafts.

Four Wheel Landing Gear

• Used on helicopters.
• Wheels typically castering.

Ski's

• Used for operation on snow.
• Two styles:
  • Wheel can be removed, and a ski placed in its place.
  • Ski goes on over the wheel, sometimes allowing the wheel to protrude through the ski.

Helicopter Ski's

• Called "bear paws".
• Attach to skids and widen the ski profile to prevent sinking into snow.
• Function more like "snowshoes".

Hulls

• Referred to as "flying boats".
• Have outrigger pontoons to support the wings.

Floats on Helicopters

• Used for emergency water landings or as main gear.

Floats on Fixed-Wing Aircraft

• Primary purpose is to land and takeoff on water.
• Consist of two large pontoons supporting the aircraft's weight.
• Use rudders for low-speed steering.
• Rudders retract for high-speed stability.
• Some have one large float and two smaller outrigger floats at the wingtips.

Amphibians

• Aircraft that can operate on both water and land.
• Consists of floats with protruding wheels, or retractable wheels for water operation.
• "Flying Boats" are a type of Amphibian.

Fixed Gear

• Most small aircraft use fixed gear.
• More efficient at slower speeds.
• Weight savings minimize drag even with streamlined "pants".
• Direct attachment to the aircraft structure.
• Shock is absorbed by tire elasticity.

Fixed Bungee Cord

• Uses rubber to cushion shock loads.
• Includes rubber donuts or bungee cords.
• Bungee cords absorb both landing and taxi loads.

Fixed Shock Struts

• Most common shock absorber.
• Called "oleo struts".
• Cylinder is attached to the aircraft, and a piston is free to move inside.
• Torque or Scissor links hold the piston and cylinder together.