Aircraft Landing Gear Presentation PDF

Purpose of Landing Gear The purpose of landing gear seems obvious. It is primarily there to absorb the shock loads of landing, and allow for steering the aircraft when it is on the ground. Many different types of landing gear. Different Types of Landing Gear The first gear was ski’s / s...

Purpose of Landing Gear The purpose of landing gear seems obvious. It is primarily there to absorb the shock loads of landing, and allow for steering the aircraft when it is on the ground. Many different types of landing gear. Different Types of Landing Gear The first gear was ski’s / skids on the Wright flyer. Different Types of Landing Gear The first aircraft with wheels, had tricycle gear. In a tricycle configuration the main wheels are located behind the center of gravity causing the nose to pivot downward, and an auxiliary wheel is placed under the nose.  When engine technology replaced the pusher props and props were mounted out front (radial engines) than the tricycle gear was replaced with the tail wheel landing style.  Big Engines Large Props The tail wheel design was developed to increase the distance between the prop and the ground. This became so popular that it is called “conventional gear.” This configuration has the disadvantage of being difficult for ground maneuvering. When engine technology advanced so the engines could now produce more power at speeds that would allow for shorter props then the tricycle gear popularity came back. This is mainly due to the superior ground handling advantages.  Tail Wheels Rudder pedals attached to the tail wheel. Cables and springs. To allow for steering. Some are fully castering…must be locked in streamlined position for take-off and unlocked for landing. To steer this type you would have to use independent braking. Ground Looping!!!  Nose wheels Most popular. Nose wheel connected to rudder for steering. Some large aircraft would use hydraulics to steer. Some have independent steering wheels or yokes for ground maneuvering.  Main Wheels The number and location vary on the use of the aircraft. Some main gear have two wheels. Multiple wheels spread the weight of the aircraft over a larger surface. Multiple wheels also provide a safety margin should one tire fail. Heavier aircraft will use 4 or more wheels. When more than two wheels are attached to a single strut the attaching mechanism is called a “boggie or truck”.  Tandem Wheels Main gear is in line down center of fuselage. Examples: Gliders and or Harrier jet. This type of arrangement has outrigger wheels supporting the wings.  Skids Found primarily on Helicopters. Have been used on aircraft.  Four Wheel Landing Gear Used on Helicopters. Wheels normally castering.   Ski’s Used for operation on snow Two Styles used on Aircraft. Wheel comes off and the ski goes on in place of. Ski goes on over wheel…sometimes the wheel is allowed to protrude through the ski bottom for operation on tarmac.  Helicopter Ski’s Ski’s on Helicopters called “bear paws” attach to skids. Designed to widen the skid profile to prevent the skid from sinking into the snow. Note: More like a “snow shoe” than a ski.  Hulls These are commonly referred to as “flying boats”. Will have outrigger pontoons to support the wings.  Floats on Helicopters Used for emergency purposes…ditching into water…or Can be main gear.  Floats Primary purpose - to be able to land and take off of water. Consists of two pontoons that are large enough to support the aircraft’s weight o the water. Use rudders to steer the floats during low speed maneuvering. Rudders must be able to retract for high speed operations. (Too sensitive at high speed.) Some aircraft use one large float under the hull with two smaller outrigger floats at the wing tips. To stabilize the aircraft.  Amphibians Term used to describe an aircraft that can be operated on the water as well as on land. This can consist of a set of floats with wheels that protrude from the float hulls or are retractable for water operation. This term is also used to describe flying Boats that have landing gear that retracts into the hull for water operations.  Fixed / Rigid Gear Most small aircraft have fixed gear. This is because the aircraft fly slowly enough that they gain efficiency by using fixed gear. The weight savings make up for the additional drag inefficiencies, especially when the wheels are enclosed in streamlined wheel fairing or “pants.” Small aircraft and helicopters that normally land softly have their landing gear directly fixed to the structure of the aircraft. Some of the shock is absorbed by the elasticity of the tires.  Fixed / Bungee Cord Some aircraft use rubber to cushion the shock loads. Can be rubber donuts (Beaver) Can be bungee cords. The bungee cord suspension excepts both landing and taxi loads.  Fixed / Shock Struts Most common used shock absorber is the air/ oil shock absorber more commonly called an oleo strut. The cylinder is attached to the aircraft and a close fitting piston is free to move up and down inside the cylinder. The two pieces are held together with torque links or scissors links.  Retractable Gear As the speed of the aircraft increases, the parasitic drag from a fixed gear offsets the advantage of its lightweight hence it becomes advantageous to retract the gear into the wing or fuselage. This can be done: Mechanically with sprockets and chains and a hand crank Electrically with motors and actuators Hydraulically Pumps, actuators, lines and valves. Any way you do it you need a system to put the gear down in an emergency.