11.13 Landing Gear Flashcards
What two types of landing gear are there
Nose wheel type (1 nose 2 main gear)
Tail wheel (2 nose 1 main gear)
What type of landing gear do all jet aircraft have
Nose wheel type (Directional stability for take off and landing)
Where is the centre of gravity on tail wheel aircraft
Aft of main wheels
Additional turning moment when landing on wet or icy runway
How is the brake out moment influenced
Greater at higher speeds
Further the centre of gravity behind the wheels
Closer the main landing gears are together
Where is the centre of gravity in nose wheel aircraft
Before main wheels
Returning moment around the centre of gravity on landing prevents ground loop of aircraft
In relation to brakes, what is an advantage of nose wheel aircraft
More forceful application of brakes, landing at lighter speeds with out nosing over
What does a greater angle of attack on nose wheel aircraft allow
Greater decrease of lift on touchdown
What is the weight carried on the main wheels called
Main wheel loading
What are 4 or 6 wheel landing gears called
Bogies
How does the nose gear retract
Forward into the fuselage
How far can the rudder pedals steer the aircraft
80’degrees left or right
On what aircraft are hydraulic powered steering systems used
Heavy aircraft
Transmit signals from the rudder pedals to the steering control valve
What does a shock strut do on landing gear
Absorb shock on landing
Uses compressed nitrogen and hydraulic fluid to absorb shock (dampening shock)
What transmits the landing gear shock loads from the drag strut to the aircraft structure
Trunnion link
What does the trunnion link rotate in
Spherical bearings
Transmit vertical and drag loads to airframe with out transferring torque to the structure
What is the inner cylinder of the strut made of
Ultra high tensile steel
Keep weight low
What are the torsion links used for
Allow inner cylinder to move up and down in the outer cylinder but not rotate
What is a torsion link damper used for
Counteract wheel shimmy
What is wheel shimmy and how does it occur
Rapid oscillation of the wheel to the left and right of direction of travel
Caused by uneven tire pressure, uneven runway surface, uneven tire wear
Why is the torsion link damper filled with hydraulic fluid
To keep it pressurised
What does the drag strut do
Stabilised the shock strut
What does the side strut do
Gives lateral support to the shock strut
What does the main gear actuator do
Converts hydraulic pressure into mechanical energy to extend and retract the gear
What does the gear down lock mechanism do
Ensures 2 parts cannot fold together when main gear is extended
What does the fluid metering device measure in the gear actuator
Speed at which actuator cylinder operates
What is the lock strut also called
Jury strut (always centred)
What does the Dow lock sensor do
Sense when the gear is down and locked in position
On what part of the gear is a lock pin inserted to prevent reaction on the ground
Lock strut
What is the purpose of the up lock roller on the gear up lock
Push the up lock hook out of the release position in to spring held engaged position
What oil does the shock strut use for dampening
Red mineral oil
What is the purpose of the flow orifice in the shock strut
Allows laminar flow (non resistant) one direction and turbulent flow (high resistance) the other direction
How is progressive dampening achieved in a shock strut
A tapered metering pin (fitted to the inner cylinder)
What decelerates the vertical motion of aircraft on landing in the shock absorber
High gas pressure and greater restriction of fluid flow
What does the rebound valve do in the shock strut
Restricts return flow of oil
What do the upper and lower bearings do in the shock strut
Upper bearings - keeps inner cylinder aligned with the outer
Lower bearings - Keeps inner cylinder aligned inside the outer
What does the gland housing assembly do
Seals the housing against the environment and pressurises oil
What does the main gland seal do in the gland housing assembly in the shock strut
Keeps the nitrogen gas and hydraulic pressure in the strut
What seals are used in the inner and outer cylinder of the shock strut
Inner - Dynamic seal (linear or rotational movement)
Outer - Static seal (steady or pulsating pressure)
What is the advantage of a spare seal actuating valve for shock struts
Seals do not have to be immediately replaced and can continue in service
Where are the spare seals for gland housing assembly kept
Spare seal cavities
What is the lock strut dimension ‘H’ a measure of
Extension of the inner cylinder
What is the result of too much gas or too much oil in a shock strut
Too much gas - soft strut
Too much oil - strut operates harshly
Why must the wheel gear tuck be able to be tilted
So it can be retracted in to the wheel well
Where do the body gears turn in relation to the nose gear
Opposite direction
What is the purpose of the body gear trunnion
Guides landing loads into the fuselage
What is the purpose of the side brace on the main gear
Directs forces from the body gear into the trunnion
What unit is the shock absorber on the centre gear
2 stage oleo pneumatic unit
What lever moves the connecting link in the shortening mechanism
Bell crank lever (turning the upper link)
What does the lock stay do for the nose gear
Gives secondary support for the down and locked position
Controls alignment of the folding drag strut
What are the upper and lower links made of the lockstay
Upper - aluminium
Lower - Steel
How is an unlock position maintained
Up lock roller and uplock hook
What is the purpose of a fluid metering device on a downlock actuator
Slows down the alignment of the struts and speed of the nose gear operation
What gives the nose gear down lock indications
Two proximity sensors
What does the actuator do
Converts hydraulic pressure into mechanical energy to extend or retract a gear
What is the purpose of the cantering cams
Ensure the nose gear is in straight and forward position before retraction
When does the nose gear proximity sensor give a ground signal
When the shock absorber is compressed to a certain position or when within a certain distance of their overcentre position
(Otherwise give a flight signal)
What make up the shock absorber on nose gear with 4 tubes
Sliding tube and plunger tube
Sliding tube has metering tube for oil transfer
Why do the centring cams return the wheels to the centre or neutral position
Prevent jamming when the gear is retracted
When are towing lugs designed to shear
If towing load is more than the limit
Decreases risk of damage to the sliding tube
When do you know the re servicing of oil is good in the shock strut
The overflow is free of air bubbles
Is the shock absorber kept fully compressed during air servicing
Yes
What are hydraulically powered steering systems also called
Follow up systems
What are the 2 basic methods of actuation for nose wheels steering
2 jack method
Rack and pinion method
What do the cable drums do in a mechanical steering system
Transmit inputs from the tiller to the steering cables
Does the interconnect actuator have to be retracted or extended for the rudder pedals to be connected to the nose wheels steering system
Retracted
What does the bypas valve do in the steering control
Protects system against high pressure developed in the actuator during towing
What is a cable compensator for in a steering system
Prevent fails inputs to steering control valve
When is the null point on a mechanical steering system
Pulling actuator reaching the end of its stroke
For electrical system steering, what are the two main valves
Selector valve and servo valve
What is a BSCU
Braking and steering control unit
What are the 3 methods used to overcome tyre damage from scrubbing
Bogie beam
Rotating truck beam
Single axle for main gear wheels
What is main gear steering automatically activated
When the speed decreases below a certain value
Automatically centred when speed increased above a certain value
What is the bypass valve for on the front doors
Opens the doors via gravity, up lock is unlocked
What gives signals when the doors are in the fully opened position
Proximity sensors
Where is the leg door connected to on the nose gear
Back of the nose gear leg
What fairings are used on the main doors
Hinged and fixed fairings
What do the ramps do inside the main doors
Make sure the doors do not interfere with the gear during fall extension
What are the 2 methods of locking the doors
Mechanical actuator with mechanical lock
Hook with door up p-lock and up lock roller
How are the hinged and fixed fairings attached to the aircraft
Hinged - via adjustable rod to wing skin
Fixed - attached to shock strut by studs and rods
What is the gear lever shaped like
A gear wheel
How are control inputs from the landing gear lever transmitted
Via electrical signals or mechanical cables
What indicated gear up or gear down next to the gear lever
Green and red lights
What positions are there in a mechanical and electrical gear system
Electrical - Up, Down
Mechanical - Up, Down, Off
What is an LGCIU
Landing Gear Control Interface Unit
How many way valves are selector valves for the gears
3/4 way valves
(Up selected, piston moves to the left)
(Down selected, piston moves to the right)
Off - Centre position
What is the difference between electrical and mechanical selector valves
Electrical uses a solenoid to remove hydraulic pressure
How is the gear level Locked on the ground
De-Energised solenoid
When is the hydraulic pressure isolated from the landing gear in an electrical system where there is no OFF position
When speed is above 250KTS
Safety valve closes
What shape Indicates the landing gear
2 triangles (Not visible when gear is up and locked)
If systems disagree green triangles always in front of red
What colour Indication are the doors when they are not up and locked
Amber
What does the door operating gear sequence valve do
Make sure the gear can begin to extend or retract only when the doors are fully open
How many sequence valves do the nose gear have
2
What allows the doors to be opened on the ground
Door bypass valve
What type of valves are hydraulic fuses
Safety valves
Areas danger to hydraulic leaks due to foreign objects
How is the life span for tyres calculated
Number of landings and take offs (approx 150)
How quick can a tyre accelerate under load from zero to 220kts and what temp will it reach
60’seconds (110 Celsius in heat)
What temp can tyres drop to in flight
-20 Celsius
What load can each main gear tyre carry
23,000kg
What disk brakes do small or large aircraft use
Small - single disk
Large - multi disk
How many times the load may an aircraft have to carry a heavy landing
2 times
What are the wheels on large jet aircraft mainly made of
Aluminium alloy (light and strong)
How are the wheel halves held together
Tie bolts
What prevents heat from wheels damaging the wheels and tires during normal braking
Heat shield
What temperature can brake disks reach on heavy braking
1000 Celsius
What automatically releases tyre pressure when a temperature of a wheel increases to a certain level
Fusible plug (Thermal relief plugs)
(Filled with alloy of low melting point) (Inside wheel - 300 Celsius)
(Wheel flange - 180 Celsius)
When are fusible plugs melted after extreme high energy braking
10 mins after aircraft brings aircraft to stop
What bearings do all aircraft have
Tapered wheel baring
What are Type 3 tyres
Low pressure (less than 160mph)
Greater width section in relation to rim diameter
What are Type 7 tyres
High pressure (Jet aircraft up to 225mph)
What are Type 8 tyres
Very high pressure (military aircraft up to 280mph)
What are the 3 main measures of a tire size
Width, rim diameter and outside diameter
What is the tyre carcass made of
Layers of rubber coated nylon chord fabric
What are beads in the tyre
High strength tensile steel wires embedded in rubber (1,2 or 3)
(Anchor the carcass)
How many times can tyres be retreaded before being scrapped
10
How are the vent holes in tyres usually marked
Yellow or green
What is a balance mark on a tyre and what is it coloured
Lightest part of the tyre (red dot)
What do belt plies do in the tyre
Give tyres strength in tread
Where does the carcass give give strength to the tyre
Sidewall
What do chippers do in the tyre
Improve durability in bead area
What are advantages of radial tyre over conventional tyre
Lighter and better performance
What are the disadvantages of radial tyres compared to conventional tyres
Expensive and cannot be retreaded as much
What is hydroplaning
Tyre squeezing water from under tread (lifting the tyre)
What is viscous hydroplaning
Slippery action on thin film of water, acts like a lubricant
What is reverted rubber hydroplaning
Locked tyre skidded over runway, generating friction heat and steam, lifting tyre off runway
What does a properly inflated tyre have a deflection of
32% (good tread wear)
Over inflated - less than 32%
Under inflated - more than 32%
If the tyre is deflated more than 45% how much heat is generated
More than 3 times normal heat
Why is under inflation worse than over inflation
Excessive stress, ply separation and weakening of carcass
How much is the pressure reduced by when not under load
4%
How much does the tyre pressure change for every 3 Celsius
1%
When is the tyre worn on tyres with a centre groove
When middle groove is no longer visible over length of 10cm or more
How many times can an aircraft fly when a tyre has reaches its normal wear limit
15 times
When must a tyre be removed if a chevron cut is more than
8mm deeper than the bottom of the nearest groove
What are tyre bulges caused by
Overheating in tread area
Where can you find the wheel interface (transmission unit)
On the axle of the wheel
What do the pistons change in a brake piston housing
Hydraulic brake pressure into load
What is an advantage of a self sealing coupling in a break piston housing
Do not have to bleed the brakes after installation
What is the purpose of the adjuster in brakes
Responsible for brake clearance and compensate for brake wear
What does the torque tube do in the brake
Transmits the torque of the stator disks to the piston housing
(Done by splines)
What does the heat pack in the brake consist of
Rotors and staters
When brake pressure is applied friction between these give braking effect
What are the advantage of carbon packs over steel packs
Around a third lighter, less wear and can withstand much higher temperatures
What are the allowable temperature limits of carbon and steel heat packs after a rejected take off
Carbon: 2500-3000 Celsius
Steel: 1500-2000 Celsius
What are the disadvantages of carbon to steel heat packs
More expensive
However can be recycled (2 used can be made in to 1 new one)
What is the metal drive block for on carbon heat packs
Protects the carbon disk during installation on the axle and wheels are being installed on brake unit
What gives a visual indication of the overall wear of the heat pack
Wear indicator pin (Pack does not have to be removed)
Fully worn when pins align with bracket
How many landings does 1mm of pin length correspond to on brakes
20-30
What must be ensured when checking for brake wear
Parking brake is on
Brakes are cold
What do the brake pedals operate on large aircraft with power braking
A metering valve (more pressure to brakes)
What is differential braking
Independently operating left hand or right hand brakes
What are the brake pedals connected via
Connection rods
What hydraulic system normally powers the normal brake metering
4 (1 as backup)
What does in flight braking do
Stops rotation movement of the wheels during retraction
Generates high Gyro movement
What is the BSCU
Braking Steering Control Unit
Controls normal braking, automatic braking, in flight braking, anti skid, nose wheel steering and temperature monitoring
What does the brake pressure transducer do
Limits the brake pressure in proportion to brake pedal travel
What gives the artificial feel at the brake pedals
Master cylinder
What powers the parking brake when the hydraulic power is switched off
Accumulator pressure
If that decreases then restored with electrical pump
When does the anti skid automatically turn off
When the aircraft is below a certain speed ( e.g. 10 KTS)
Avoids danger of releasing brakes when not wanted
What is the brake release signal for each wheel
2 sets of 4 green lines
Why would and automatic brake system be used
Reduce delay between touchdown and application of brakes (Less than 1 second)
Each second delay reduces stopping distance by 60m
How much increase of drag do speed brakes give
40-80%
When are the speed brakes applied (% of aircraft weight on wheels)
65%-90% weight on wheels
What does the servo valve do for the brakes
Sends pressure to the brakes
What does the deceleration rate depend on
Runway length
What rate of deceleration is selected when a blue light illuminates
Medium deceleration, auto braking system armed
What colours are 0-4 and 5-9 for brake temp
1-100 Celsius) (9-865 Celsius
0-4 white
5-9 amber above 300 Celsius
How is temperature of wheel brakes measured
Thermocouple
How are brakes cooled
Electrically driven cooling fan
3 phase motor
What are micro switches
Switch devices that can open and close an electrical circuit at very high speeds
What do 3 greens indicate
Landing gear is down and locked
Amber light - gear in transit and not locked
