Landing gear.pdf

AIRCRAFT SUB-SYSTEMS ELEMENT (ESA 272) Landing Gear Systems Dr. Nurul Musfirah Mazlan Landing Gear Systems Introduction Landing gear designs for aircraft vary from fix arrangements to complex retractable. This chapter examines typical examples of landing gear and the systems by which they...

AIRCRAFT SUB-SYSTEMS ELEMENT (ESA 272) Landing Gear Systems Dr. Nurul Musfirah Mazlan Landing Gear Systems Introduction Landing gear designs for aircraft vary from fix arrangements to complex retractable. This chapter examines typical examples of landing gear and the systems by which they are operated. Introduction 2 Landing Gear Configurations Aircraft landing gear can be classified as either tricycle or conventional. Conventional geared aircraft: – Have two main wheel assemblies, one on each side of the aircraft, and a tail wheel. – 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. Landing Gear Configurations 3  An aircraft with a conventional landing gear Landing Gear Configurations 4  Tricycle landing gear: – Having a nose wheel assemblies and two main gear assemblies on each side of the aircraft. – Aircraft fuselage in a level attitude on the ground. – Advantages Cabin area is level, for passengers to move easily inside the aircraft. Stable on the ground. Easy to control when taxiing, during takeoff and landing. Landing Gear Configurations 5  Tricycle landing gear with dual main wheels on a Learjet (left) and a Cessna 172 also with tricycle gear (right) Landing Gear Configurations 6  Classification of landing gear – Main landing gear (main support of the airplane on land or water): Combination of wheels, Floats, Skis Shock absorbing equipment Brakes Retracting mechanism Control, Warning device Cowling, 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 Landing Gear Configurations 7 Main Landing Gear Landing Gear Configurations MEA322 Landing Gear Systems 2015 8  Nonabsorbing Landing Gear – Rigid landing gear Helicopters and sailplanes Rely pilot skill for soft ground contact – Shock-cord landing gear Used rubber shock cord – Spring-type gear Single, tapered strips or tubes of spring steel or composite material Landing Gear Configurations 9  Shock-Absorbing Landing Gear – Spring-oleo Struts (piston and coiled spring): Piston and cylinder arrangement provides an oil chamber and an orifice through which oil is forced during landing. The spring supports the aircraft on the ground, the oleo strut absorbs the shock of landing. Landing Gear Configurations 10  Shock-Absorbing Landing Gear – Air-oleo Principle operation is similar for all struts. The compressed air in the chamber supports the aircraft on the ground and act as shock absorber during taxiing. Can be used for either nonretractable or retractable landing gear. Landing Gear Configurations 11  Fixed Gear – Nonretractable (fixed) landing gear is attached to structural members of the airplane. – Often equipped with fairing to reduce the drag. – Wheel pants are used to cover the wheel and tire to reduce the drag. – Usually found on small aircraft. Landing Gear Configurations 12  Fixed gear Landing Gear Configurations 13  Retractable Landing Gear – Developed to eliminate the drag caused by the exposure of the landing gear to airflow during flight. – The retraction is accomplished with hydraulic or electric power. – In emergency, backup hydraulic systems, stored air or gas can be directed into actuating cylinders mechanical systems (operated manually) or free fall gravity systems. – Much more complex, primary importance in the safe operation of the aircraft. Landing Gear Configurations 14  The retractable gear of a Boeing 737 fair into recesses in the fuselage. Panels attached to the landing gear provide smooth airflow over the struts. The wheel assemblies mate with seals to provide aerodynamic flow without doors. Landing Gear Configurations 15 Landing Gear Components Landing gear assemblies are made up of various components. The following terms identify many of this components and presented here as they related to retractable landing gear systems. 1. Trunnion 2. Struts 3. Torque Links 4. Truck 5. Drag Link 6. Side Brace Link 7. Overcenter Link 8. Swivel Gland 9. Shimmy Dampers Landing Gear Components 16 1. Trunnion – Is the portion of the landing gear assembly attached to the airframe. – Supported by bearing assemblies. Landing Gear Components 17 2. Struts – Is the vertical member of the landing gear assembly. – Contains the shock- absorbing mechanism. – Also called outer cylinder. Landing Gear Components 18 3. Torque Links – Often referred to as a scissors assembly. – Used to connect the strut cylinder to the piston and axle. – Hold wheels and axle in a correctly aligned position. Landing Gear Components 19 4. Truck – Located on the bottom of the strut piston and has the axles attached to it. – Is used when wheels are to be placed in tandem or in dual tandem arrangement. – Can tilt fore and aft. – Often referred as a bogie. Landing Gear Components 20 5. Drag Link – Is designed to stabilize the landing gear assembly longitudinally. – If the gear retracts forward and aft, the drag link will be hinged in the middle. – Also called a drag strut. Landing Gear Components 21 6. Side Brace Link – Is designed to stabilize the landing gear assembly laterally. – If the gear retracts sideways, the side brace link is hinged in the middle. – Also called a side strut. Landing Gear Components 22 7. Overcenter Link – Used to apply pressure to the center pivot joint in a drag or side brace link. – The overcenter link is hydraulically retracted to allow gear retraction. – Also called a downlock and a jury strut. Landing Gear Components 23 8. Swivel Gland – Is a flexible joint with internal passages that route hydraulic fluid to the wheel brakes and the bungee cylinder of a landing gear. – Used where bend radius is too small or space limitations. – May be mounted on a bracket secured to the main-gear trunnion fitting. Landing Gear Components 24 9. Shimmy Dampers – Is a hydraulic snubbing unit that reduced the tendency of the nose wheel to oscillate from side to side. – Two design, piston and vane type. – Both of which might be modified to provide power steering as well as shimmy damper action. Landing Gear Components 25  Drawing of a Principle of a piston-type shimmy damper vane-type shimmy damper Landing Gear Components 26 Tires and Wheels Aircraft tires support the weight of the aircraft while it is on the ground and provide the necessary traction for braking and stopping. The tires also help absorb the shock of landing and cushion the roughness of takeoff, rollout, and taxi operations. Tire Classification 1. Type. 2. Ply rating. 3. Tube-type or Tubeless. 4. Bias ply tires or Radials. Tires and Wheels 27 1. Type. A common classification of aircraft tires is by type as classified by the United States Tire and Rim Association. Type Design and Rating I Smooth contour II High pressure III Low pressure IV Extra low pressure V Not applicable While there are nine types VI Low profile of tires, only Types I, III, VII, VII Extra high pressure, low speed and VIII, also known as a Extra high pressure, high speed Three-Part Nomenclature VIII Extra high pressure, low profile, low speed tires, are still in Extra high pressure, low profile, high speed production. Tires and Wheels (Tire Classification) 28  Type I tires are manufactured, but their design is no longer active. They are used on fixed gear aircraft and are designated only by their nominal overall diameter in inches. These are smooth profile tires that may be found on older aircraft. Tires and Wheels (Tire Classification) 29  Type III tires are common general aviation tires. They are typically used on light aircraft with landing speeds of