Aircraft Landing Gear PDF

Aircraft landing gear - supports the entire weight of an aircraft during landing and ground operations. Skis - Aircraft that operate to and from frozen lakes and snowy areas Pontoon-type landing gear. - Aircraft that operate to and from the surface of water Basic landing gear types inc...

Aircraft landing gear - supports the entire weight of an aircraft during landing and ground operations. Skis - Aircraft that operate to and from frozen lakes and snowy areas Pontoon-type landing gear. - Aircraft that operate to and from the surface of water Basic landing gear types include those with wheels 1. Skids 2. Skis 3. Floats or Pontoons Amphibious aircraft - designed with gear that allow landings to be made on water or dry land. - the skis are retractable to allow use of the wheels when needed. Three(3) Basic Arrangements of Landing Gears: > Tail Wheel-Type Landing Gear (Conventional Gear) > Tandem Landing Gear > Tricycle-Type Landing Gear Tail Wheel-Type Landing Gear - It is also known as conventional gear because many early aircraft use this type of arrangement. - The main gear are located forward of the center of gravity, causing the tail to require support from a third wheel assembly. Steerable tail wheel - connected by cables to the rudder or rudder pedals, is also a common design. - Springs are incorporated for dampening. Tandem Landing Gear - This type of landing gear has the main gear and tail gear aligned on the longitudinal axis of the aircraft. - Sailplanes commonly use tandem gear - military bombers, such as the B-47 and the B-52, have tandem gear, as does the U2 spy plane. Tricycle-Type Landing Gear - The most commonly used landing gear arrangement is the tricycle-type landing gear. - It is comprised of main gear and nose gear. Tricycle-Type Landing Gear benefits: 1. Allows more forceful application of the brakes without nosing over 2. Provides better visibility from the flight deck 3. Prevents ground-looping of the aircraft. The nose gear of a few aircraft with tricycle-type landing gear is not controllable. On light aircraft, the nose gear is directed through mechanical linkage to the rudder pedals. Heavy aircraft typically utilize hydraulic power to steer the nose gear. Control is achieved through an independent tiller in the flight deck. The main gear on a tricycle-type landing gear arrangement is attached to reinforced wing structure or fuselage structure. Many main gear have two or more wheels. Multiple wheels - spread the weight of the aircraft over a larger area. - provide a safety margin should one tire fail. - Heavy aircraft may use four or more wheel assemblies on each main gear. Bogie When more than two wheels are attached to a landing gear strut. Tricycle-type landing gear arrangement consists: air/oil shock struts gear alignment units support units retraction and safety devices steering systems wheel and brake assemblies, etc. Two classification of aircraft landing gear: 1. Fixed 2. Retractable Fixed - small, single-engine light aircraft have fixed landing gear, as do a few light twins. - means the gear is attached to the airframe and remains exposed to the slipstream as the aircraft is flown. Retractable - stow in fuselage or wing compartments while in flight. - Most retractable gear have a close-fitting panel attached to them that fairs with the aircraft skin when the gear is fully retracted. - Other aircraft have separate doors that open, allowing the gear to enter or leave, and then close again. The forces of impact on an aircraft during landing must be controlled by the landing gear. This is done in two ways: 1. the shock energy is altered and transferred 2. the shock is absorbed by converting the energy into heat energy. Types of Shock Absorbing and Non-Shock Absorbing Landing Gear: > Leaf-Type Spring Gear > Rigid > Bungee Cord ≥ Shock Struts Leaf-Type Spring Gear - The gear flexes initially and forces are transferred as it returns to its original position. - The most common example of this type of non-shock absorbing landing gear are the thousands of single-engine Cessna aircraft that use it. - this type made from composite materials are lighter in weight with greater flexibility and do not corrode. Non-shock absorbing struts made from: Steel Aluminum Composite material Rigid - many early aircraft were designed with rigid, welded steel landing gear struts. - Shock load transfer to the airframe is direct with this design. - Use of pneumatic tires aids in softening the impact loads. - Modern aircraft that use skid-type landing gear make use of rigid landing gear with no significant ill effects. (ex. Rotorcraft) Bungee Cord - The use of bungee cords on non-shock absorbing landing gear is common. - allows the strut assembly to flex upon landing impact. - positioned between the rigid airframe structure and the flexing gear assembly - made of many individual small strands of elastic rubber. Piper Cub bungee cord landing gear - transfer landing loads to the airframe (left and center). Rubber, donut-type shock - transfer is used on some Mooney aircraft (right). Shock Struts - True shock absorption occurs when the shock energy of landing impact is converted into heat energy. - the most common method of landing shock dissipation in aviation. - Shock struts are self-contained hydraulic units - They must be inspected and serviced regularly to ensure proper operation. - sometimes referred to as an air/oil or oleo strut. A typical pneumatic/hydraulic shock strut uses compressed air or nitrogen combined with hydraulic fluid to absorb and dissipate shock loads. A shock strut is constructed of two telescoping cylinders or tubes - The upper cylinder is fixed to the aircraft and does not move. - The lower cylinder is called the piston and is free to slide in and out of the upper cylinder. Two chambers are formed. - The lower chamber is always filled with hydraulic fluid - the upper chamber is filled with compressed air or nitrogen. Orifice - located between the two cylinders provides a passage for the fluid from the bottom chamber to enter the top cylinder chamber when the strut compressed. Metering Pin - for controlling the rate of fluid flow from the lower chamber into the upper chamber. Metering tube - this is used on some types of shock struts. - the holes in the metering tube control the flow of fluid from the bottom chamber to the top chamber during compression. Recoil valve - restricts the flow of fluid during the extension stroke, which slows the motion and prevents damaging impact forces. Axle - provide installation of the aircraft wheels. Upper cylinder - contains a valve fitting assembly. - It is located at or near the top of the cylinder. Valve - provides a means of filling the strut with hydraulic fluid and inflating it with air or nitrogen as specified by the manufacturer. Packing gland - employed to seal the sliding joint between the upper and lower telescoping cylinders. It is installed in the open end of the outer cylinder. Packing gland wiper ring - It is designed to keep the sliding surface of the piston from carrying dirt, mud, ice, and snow into the packing gland and upper cylinder. Torque links or torque arms - To keep the piston and wheels aligned Shimmy Damper - helps control oscillations of the nose gear. Upper locating cam - mates into a lower cam recess when the nose landing gear shock strut is extended before landing and before the gear is retracted into the wheel well. locking or disconnect pin - enable quick turning of the aircraft while towing or positioning the aircraft when on the ramp or in a hangar. Jacks - should always be placed under the prescribed points. towing lug - designed means for attaching a tow bar. instruction plate - gives directions for filling the strut with fluid and for inflating the strut. Sleeves spacer or bumper ring - limits the extension stroke Two common types of high pressure strut servicing valves 1. Valve-core type 2. Core-free valve fittings swivel nuts - engage threads on an internal stem that loosens or draws tight the valve stem to a metal seat. Bleeding Shock Struts - This can be caused by low hydraulic fluid quantity in the strut - normally done with the aircraft on jacks to facilitate repeated extension and compression of the strut to expel the entrapped air. manufacturer's maintenance instructions - give the procedure for checkin; and adjusting tow-in or tow-out. straight edge - held across the front of the main wheel tires just below axle height. carpenter's square - placed against the straight edge creates a perpendicular that is parallel to the longitudinal axis of the aircraft. A gap in front indicates the wheel is towed-in. A gap in the rear indicates the wheel is towedout. Camber - is the alignment of a main wheel in the vertical plain. - camber is said to be positive if the top of the wheel tilts outward from vertical. - Camber is negative if the top of the wheel tilts inward. trunnion - fixed structural extension of the upper strut cylinder with bearing surfaces that allow the entire gear assembly to move. drag brace - is used to restrain against the pivot action built into the trunnion attachment. electric/hydraulic system also known as power pack system Restrictors - used in the nose wheel actuator inlet and outlet ports to slow down the motion of this lighter gear. Large aircraft retraction systems are nearly always powered by hydraulics. Auxiliary Electric Hydraulic Pumps are also common Gear indicators - used to communicate to the pilot the position status of each individual landing gear at any time. Squat Switch or Safety Switch - This is a switch positioned to open and close depending on the extension or compression of the main landing gear strut. Solenoid - extends a shaft to physically disable the gear position selector is one such method found on many aircraft electromagnetic sensor - returns a different voltage to a gear logic unit depending on the proximity of a conductive target to the switch. Go-no go gauges - used to set the distance Ground locks - commonly used on aircraft landing gear as extra insurance that the landing gear will remain down and locked while the aircraft is on the ground. Landing Gear Position Indicators - used to inform the pilot of gear position status. - blinking indicator lights indicate gear in transit - green lights means it is safe to land - all lights out indicates that the gear is up and locked ramp/track - guides the roller or pin in such a manner that the nose wheel is straightened as it enters the wheel well. Dust and sand mixed with grease produce a very destructive abrasive compound. When cleaning a wheel bearing, use the recommended cleaning solvent. Do not use gasoline or jet fuel. To lubricate a tapered roller bearing, use a bearing lubrication tool or place a small amount of the approved grease on the palm of the hand. Over-travel - action of the cylinder piston beyond movement necessary for landing gear extension and retraction. Latches - used in landing gear systems to hold the gear up or down and/or to hold the gear doors open or closed. Cables - are connected to the sector to permit emergency release of the latch rollers. locking link - It is adjustable to provide the correct amount of over-center travel of the side brace links. Collapsible side brace - common geometry used to lock landing gear in the down position