Module 11.13 Landing gear Flashcards
How is the main landing gear installed in a tail wheel configuration?
In front of the CoG
Where are the main landing gear in reference to the CoG in a tricycle configuration?
Behind the CoG, this prevents ground looping
What is a tandem gear configuration? How is it supported laterally?
Two gear aligned longitudinally
Outrigger gear give support
What do fixed gear increase?
In-flight drag
What gear would have a drag strut?
Gear that retract in the fore and aft direction i.e. Nose Landing Gear NLG
What is the side and drag strut in gear connected to?
The outer structure of the cylinder and the structure of the aircraft
How is the side/drag strut held in place?
By a downlock mechanism/lock stay
How is the side strut locked?
Downlock pulled into over centre position this is then held by two strong downlock springs
What is the purpose of the shortening link?
To shorten gear during retraction so it can fit in the wheel well
What does the gear pivot about?
Trunnion
What stops the gear spinning and falling out of the outer cylinder?
Torsion link
What is the purpose of cams in the NLG?
Upper and lower locating cam come together to centre the gear when there is no weight on the wheels
Some NLG have a torque link damper, what is the purpose of this? Cause?
Shimmy damper, stops shimmy of the axle cause by uneven, pressure, wear or runway surface
What are the two classes of shock absorbers?
- Solid
- Oleo-pneumatic
What is the strut partially filled with?
Oil and nitrogen gas
What do some oleo-pneumatic shock absorbers have?
Separator between oil and gas
The cylinders are free to extend within the range of what?
The torsion link
When weight is applied to the wheels, what reduces the movement of fluid between the upper and lower oil chambers?
Flutter plate with restrictor valves
What occurs to the shock absorbers when a force is applied? i.e. landing
Weight applied to wheels which compresses the gas this then forces the piston up. This moves the inner cylinder up and fluid to transfer from upper to lower chamber through the flutter plate
What occurs after the initial compression of cylinders?
Recoils back to an extended position
What is the shock strut dimension ‘X’ or ‘H’?
Extension of inner cylinder with weight on wheels
Where may the correct dimensions ‘X’ be found?
In graph with measured gas pressure and actual shock strut temperature
In normal extension/retraction how should the gear be moved?
Movement should be powered
What is the only movement with a backup/emergency?
Extension
How are the different extension/retraction conditions commanded?
Normal - lever
Emergency - Separate lever/handle
How is the lever protected from moving under vibration or accidental movement?
Detents
When the aircraft is on the ground, what stops the gear lever being moved?
Solenoid operated latch to stop movement. This is in the closed position when the power is off
Why is sequencing needed in gear movement?
To allow the doors to open prior to gear movement
What is the process of gear extension?
- Door uplock released
- Door opened
- Gear uplock released
- Gear down
- Door close
What should be installed to lockstay during towing?
Locking pins
Emergency extension handles are connected to what via a mechanical linkage?
Gear uplock
How is the gear held in place in the wheel well when the gear is retracted?
Up-lock hooks
Before operation of the emergency extension handle, why must the landing gear selector be placed in the off position?
Shut off system pressure and connect actuator chambers, ‘ damping mode’. Prevent hydraulic lock
Visual indication of what is given during extension and retraction?
Position of gear and doors
Where are position sensors located in gear systems?
- Gear up-lock
- Gear down-lock
- Door Up-lock
What are microswitches used to monitor?
Position of:
- Valves
- Gears
- Doors
When would a proximity switch be used instead of normal microswitch?
In areas of corrosion and contamination
What are the two different types of proximity switch?
- Reed switch
- Electronic switch
When would a microswitch be used?
Where physical contact is permissible
What does the sensor consist of in a reed switch?
Two spring loaded contacts, that are normally open, in a glass tube filled with gas to stop corrosion
How are the contacts closed so that the circuit operates the indicator?
Target is moved close to the sensor. The target has a magnetic field. No contact is needed
In the electronic proximity switch, what is the target and sensor?
Target - non mag ferrous material
Sensor - Sensing coil
What occurs to the coil when the target is nearby?
Varied impedance, triggers switching function
How is the wheel supported on the axle?
Tapered roller bearing
Aircraft wheels are made from what?
Forged or cast, aluminium alloy some are made from magnesium alloy
How are modern aircraft wheels constructed?
Two half hubs, inboard and outboard, that carry a tubeless tyre
What half of the wheel are the brake units attached to?
Inboard
How are the brake discs and wheels mated?
Steel drive keys bolted to the inside of the wheel
What prevents brake heat from damaging the wheels during normal braking?
Heat shield
What is the purpose of fusible plugs?
They release tyre pressure when the temperature exceeds a certain level, this is because it is plugged with a low melting point alloy
Where are fusible plugs not installed and why?
In the NLG as there are no brakes there
What half of the wheel are the fusible plugs in?
Inboard half
What half of the wheel is the inflating valve?
Outboard half
What half of the wheel are the tapered roller bearings?
Both
How are small light aircraft typically braked?
Using a single brake discs which is keyed or bolted to the wheel and turns with the wheel
Where are the 6 brake lining/pucks located?
3 are attached to each piston and the other 3 are stationary on the other side of the disc
When would dual discs brakes be used?
On aircraft that require more friction to slow them down i.e. heavier aircraft
What is located between the two discs?
Friction lining
What is the auto adjusting pin or wear indicating pin used for?
To indicate the wear of the friction lining
Large aircraft require multiple disc brakes, what are the main components of these?
- Torsion tube
- Piston housing
- Heat pack
What has slots to engage with the drive keys on the inboard half of the wheels?
Rotors
What is the wear indicating pin located on in a multi disk brake pack?
The stators
When should the wear indicating pin be checked to see if there is sufficient material on the stator?
When the brakes are applied
What is the benefit of carbon packs?
- 40% lighter than steel packs
- Can deal with 50% higher temperatures than steel
- 20-50% longer life
What is the advantage to segmented brakes?
Less bending due to heat
If a pack has 14 pistons how many hydraulic systems supply these?
1 - Supplies 7 called the normal braking
1 - Supplies 7 called the alternate braking
How is the switch between normal and alternate braking made and via what?
It is done automatically and via a shuttle valve
What controls the hydraulic fluid to the brakes?
Brake control valve
Where would the brake debooster be located?
Between the brake control valve and the user
How is the parking brake pressure kept?
Via a shutoff valve
How is permanent pressurisation of the parking brake maintained?
Brake accumulator
What does the ant skid system do?
Senses skid by changed in difference between a/c speed and wheel speed. It will release the brakes for a brief period
In an electronic system where would the anti skid valve be located?
After the brake control valve before debooster
What is the wheel speed sensor called?
Tacometer
How are tyres classified?
- Width
- Rim diameter
How are tyres categorised?
- Tubed
- Tubless
What is the fabric layer assembly in a tyre called?
Carcass
What angle of plies in a bias?
30° and 60°
What angle are radial plies laid?
90° to the direction of wheel spin
What keeps the tyre on the wheel?
The bead
What does the red dot signify on a tyre?
Lightest point of the tyre
What do the green dots signify on a tyre?
Small holes to let out entrapped gases
What carries the stator rotor assembly?
The torque tube
In an emergency what provides brake pressure?
The brake accumulator
When must brake not be applied?
At touchdown, as it can cause a blowout
In touchdown protection, what valve is controlled?
The anti skid valve
What is the purpose of auto brake?
To stop the aircraft at a certain deceleration rate without the pilots input
When would each auto brake position be used?
- Low and medium normal landing
- Max on a rejected take off
What is on ramp stage of landing roll?
- Smooth build up of pressure to the desired deceleration rate
What is on auto braking stage of landing roll?
- Constant brake pressure level
What is on off ramp stage of landing roll?
- Smooth decrease in brake pressure, initiated when the speed brakes retract or pilot operates the brakes
How can the aircraft be steered if the NLG steering is in operative?
Differential braking
How is the NLG steered?
By moving the rotatable collar
On the NLG what is the upper tension link attached to?
The rotating collar
How may the rotatable collar be actuated?
Hydraulically or mechanically
What gear would a shimmy damper be fitted to?
NLG
Where would a shimmy damper be fitted?
On the torsion link or collar
Why may the aircraft have main gear steering?
To reduce tire scrubbing
Is the main gear steering angle more or less than the NLG?
Less
- 5° - 8°
What must be done the NWS before towing?
Depressurised or isolated
Air ground sensing uses what sensor?
Proximity sensor
Where are the proximity sensors located?
Shock struts
What is used also on 4-6 wheel MLG to help air ground sensing?
Bogie bar
In modern aircraft (brand new) what may be used instead of proximity sensors?
Load sensors on landing gear beam
