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| Company Name : |
| Spirit AeroSystems Malaysia Sdn Bhd |
| Industry : |
| Aerospace / Aviation / Airline |
| Type of Company : |
| Private Limited Company |
| Location : |
| Pusat Aeroangkasa Antarabangsa Malaysia (MIAC), LTSAAS, Subang, 40150 |
Some a/c have free castering nose wheels; most have steerable.
Uses foot power to steer the aircraft – no assistance
Some types will disengage when the gear is retracted
Some types have an automatic centering device when weight is off the a/c
Conventional gear use the tail wheel to steer
May be a castering type with no steering capabilities (rudder steers)
May be lockable, for parking purposes
Used where large amounts of force are required to steer
Controlled by pilots rudder pedals, OR
By a steering wheel, OR
By a combination of both
Most will require a towing bypass valve which allows
Ground crews to to the a/c without damaging the system
Purpose: reduce drag, or adapt a/c for landing on different surfaces
(consider retractable wheels on float systems)
Crank mechanism, or uses a lever pulled by the pilot
This method may use a mechanical latch system to lock wheels “up”
No emergency backup available for this system
Uses a central motor and push-pull rods
Uses microswitches to detect when gear is down/locked, or up/locked
Most common system of retraction for most sizes of a/c
Used exclusively where landing gear is too large to be retracted by other methods
May use ED pumps, electric pumps, hand or wind-driven pumps
4 possible methods of dropping gear when hydraulics are lost:
air bottle “blows” the gear down
hand crank or ratched
separate hydraulic system (may be hand pump)
mechanical system which releases UP locks, and gear free-falls
4 main components:
shock strut
the wheel
the brake assembly
the trunnion and side/drag brace
scissors (torque links)
actuating cylinder
down & up locks
the bungee system
Using hydraulics, landing gear retraction requires greater energy than lowering
Gear rotates on the trunnion pin
Extending landing gear requires a release of the UP lock first, then
The gear can begin free falling, slowed by the snubber in the orifice check valve
Final few degrees of travel may require hydraulic pressure assistance
Bungee system is used for emergency operation:
Gear doors must be operated before extension & after retraction
Positive indication must be provided to the pilot that gear is down & locked
Safety system includes squat switches and other microswitches
Squat switches tell pilot when weight of a/c is on the wheels
Squate switches are electrically “open” when on the ground
Some a/c use warning horns: they sound when:
If gear is retracted, and throttle retarded to below cruise
Landing gear position indicators: show position of Landing gear
May use a system of different color indicator lights
Two main types: Conventional, and Tricycle
Tricycle
Has nose wheel, which may be steerable
Main gear, on either side
Example: Cessna
Keeps aircraft level during take-off and landing
The most important advantage is its ease of ground handling.
Conventional
Two main wheels
One tail dragger wheel
Reduced drag in the air
Reduced landing gear weight
Requires more skill in ground taxiing
The most important advantage is the ability to operate the aircraft over rough terrain.
Main landing gear
Cushions landing impact
Heavily stressed area
Main Landing Gear consists of the main weight-bearing structure
Auxiliary landing gear includes tail wheels, skids, nose wheels, etc.
Includes Rigid landing gear, Shock-cord landing gear, Spring landing gear
Rigid: helicopters, sailplanes. No flexing other than the structure.
Shock cord system: uses “Bungee” cords
Spring type uses spring steel (some Cessna’s)
Dissipates landing energies by forcing fluid through a restriction
This fluid generates heat, dissipated into the atmosphere
Two types: Spring Oleo, and Air-Oil Oleo
Spring Oleo is history by now
Air Oleos are all very similar: a needle valve restricts fluid flow
Air in the oleo holds the weight of the a/c on the ground
Air Oleos present in both retractable and fixed gears
Non retractable, usually bolted on to the structure
Often uses fairings or wheel pants
Cessna 152
Advantages:
Lighter weight
Less compex
Least costly
Designed to eliminate drag (the greatest advantage)
Can be either fully or partially retractable
Direction of retraction depends on airframe model
Methods of retraction: hydraulic, electric, mechanical, pneumatic
Critical area of aircraft maintenance for safety reasons
Can be single float, or multiple
Definition may include floating hulls (ex. “Lake” aircraft)
Floating hulls may only require wing tip floats
Skis used for snow and ice (wood, metal, composites)
Skis may use shock cord to assist angle of ski attack
Skis are mounted on the same strut as tires
Exact definitions of some components will vary
The Oleo strut is the widely used form of shock absorption on aircraft landing ge
ar.
Portion of the landing which attaches to the airframe
Supported at the ends by bearings
Landing gear traditionally extends from the center
Vertical member, contains the shock absorbing mechanism
Top of the strut mounts onto the trunnion
Strut forms the cylinder for the oleo (“outer” cylinder)
Piston is the moving portion (aka piston rod, tube or inner cylinder)
Oil is forced from the lower portion of the strut to the upper
Oil flow is restricted or varied according to a metering pin
Final weight of a/c rests on air in the top of the strut
Snubbers are used to prevent a sudden dropping of gear on takeoff
Metering pin controls the flow of fluid between the chambers.
The shock of landing is absorbed by the fluid being forced through a metered orifice. The metering pin gradually reduces the size of the orifice as the shock strut extends, which avoids a rapid extension after the initial shock of landing and related bounce.
Chevron seals are used in shock struts to prevent the oil from escaping
On nose wheel struts, a cam is built into the strut for the purpose of straightening
the nose wheel before retraction.
Filling a shock strut: “exercise” the strut in order to seat the seals, and remove air bubbles from the fluid.
Most shock strut oil levels are checked by releasing the air, bottoming the strut, and checking to see if the oil is at the level of the filler plug.
Information about shock struts: see:
Manufacturer’s maintenance manual
Information decal located on the strut
Mfr’s overhaul manual
Also called scissors assembly
Two A-frame members
Connects and aligns upper and lower cylinders
Connects the strut cylinder to the piston
Restricts extension of piston during retraction
Correctly aligns axle to the strut
Located at the bottom of the strut piston
Axles are mounted on the truck
Trucks can tilt fore or aft to allow for a/c attitude changes
Stabilizes landing gear longitudiannly
May be hinged to allow retraction
Also called a drag strut
Stabilize gear laterally
May be hinged to allow retraction
Can be called a side strut
Use to apply pressure to the center pivot joint in a drag or side brace link
Overcenter link is hydraulically retracted to allow gear retraction
Also called a downlock, and/or a jury strut
Flexible joint with internal passages
Route hydraulic fluid to the wheel brakes
Used where space limitation eliminate flex hoses
Hydraulic snubbing unit
Reduces tendency of nose wheels to oscillate
Piston and rod filled with hydraulic fluid
Piston has an orifice restricting speed of travel
Slow movement has no restriction
Large shimmy dampers incorporate temperature compensation
Employ stationary vanes and rotating vanes
Small passages restrict fluid movement
Central shaft rotation is restricted from moving quickly
Check for leakage & effectiveness of operation
Check mounting bolts and hardware
Most dampers are fairly reliable
On low wing aircraft fuel pumps are required. To initially get fuel to the engine for starting, an electrical “boost pump” is turned on to pump fuel to the engine. After the engine is started, a mechanical fuel pump driven by the engine feeds fuel to the engine. The electric boost pump can now be turned off.
Each fuel tank is equipped with a drain valve located at the lowest point in the tank. This drain allows the pilot during preflight walk-around to check for and drain off any water which may have accumulated in the fuel tank. There is usually another drain located at the lowest part of the fuel piping system. This valve must also be drained during pre-flight to eliminate any water which may have accumulated in the fuel lines. Associated with this drain is a fuel strainer which filters out foreign matter which may be in the fuel system.
A vent line allows air to enter the tank as fuel is used. During hot weather, fuel may expand and overflow through the vent when tanks are full.
A fuel selector valve located inside the cockpit allows the pilot to select which tank(s) are to be in use during flight. Most small aircraft operate with the selector set on Both, such that both the left and right fuel tanks are simultaneous feeding fuel to the engine. The pilot may set the selector on Left or Right tank as a means of equalizing the loading of the aircraft. Usually, the selector should be set to both for take-off and landing. Pilots of low wing aircraft should exercise caution in their fuel management if tank selection is other than both. Running a tank dry can cause the engine to quit and vapour lock to occur in the fuel lines. It may be impossible to restart the engine under these conditions.
There is a fuel gauge in the cockpit for each fuel tank. The lower 1/4 of the fuel gauge indication is marked with a red line as a caution to the pilot of a low fuel condition. The pilot should never rely on the fuel gauge as the sole measure of fuel remaining. The gauges on aircraft are subject to a variety of indicator errors. The pilot should therefore double check the fuel remaining based on the power setting of the engine in flight and time in flight.
Inside the cockpit a fuel mixture control and a fuel primer pump are located on the instrument panel. The mixture control is used to adjust the air/fuel mixture for the altitude being flown. It allows the pilot to adjust the fuel/air ratio entering the engine. As altitude is gained, the intake air becomes less dense. Less fuel must be fed through the carburettor to permit the fuel/air mixture to remain correct proportion. If leaning is not accomplished by the pilot, a rich mixture (too much fuel) results. This is not only wasteful of fuel, but can result in fouled spark plugs due to carbon and soot buildup on the spark plugs. A rough running engine results. An additional gauge called an Exhaust Gas Temperature Gauge can be installed in the aircraft as an aid in achieving the proper “leaning” of the engine.
The fuel primer is a plunger that can be used in cold weather to inject fuel directly into the carburettor as an assist in starting the engine in cold conditions.
Three different grades of fuel are used in reciprocating engine aircraft. These grades are designated by octane rating and are colour coded so the pilot can insure the proper grade of fuel is being pumped into the tanks.
