11.13 - Landing Gear Flashcards
What is the purpose of a tapered metering pin?
Small end of the metering pin is in the orifice when extended and as the strut collapses, it’s tapered shape steadily decreases the area of the orifice.
The energy in the landing impact is absorbed by the oil as it is forced through the decreasing size orifice and by the air which compresses as the oil is forced into the upper chamber.
Define tricyle and conventional landing gear?
Tricyle landing gear - Nose wheel unit forward of 2 main landing gear units (CG ahead of main landing gear)
Conventional type landing gear - Tail wheel behind 2 main landing gear units (CG aft of landing gear units)
Explain the servicing procedure for a landing gear strut?
Volume of nitrogen determines pressure (pre-charge).
Required pre-charge is found on a graph in Maintenance Manual/landing gear strut/ landing gear door.
Jack the aircraft, strut will give a maximum reading, the strut can be brought to correct pressure by means of a pressure gauge.
Disengage nitrogen bottle, check for leakage. Strut ready
How is a nose landing gear normally centred after take off?
As the strut extends, centring cams in the inner and outer struts ensure the wheel is in the correct position.
What is used to hold a landing gear down and locked?
Overcentre links which remain in position by means of the spring force of the bungee springs.
(Overcentre link between strut and side brace)
Explain the use of a trim cylinder?
A trim cylinder or tilt cylinder ensures the bogie beam (axle carrier) is at the correct angle to fit into the wheel well.
What is the purpose of sequence valves?
Sequence valves ensure operation of the hydraulic components according to a fixed sequence at the correct time and in the correct way.
(Gear extension and retraction sequence)
What happens to the hydraulic system when the emergency extension is actuated?
In this case, the hydraulic fluid must be able to flow around all hydraulically operated cylinders.
For this reason, a bypass valve is opened as the emergency extension system is operated.
What is the purpose of the green, red and amber lights for landing gear indication?
Green = the landing gear is ‘‘down and locked’’
Red = The landing gear is moving ‘‘up’’ or ‘‘down’’ (in transit)
Amber = The wheel doors are not closed
What position is the gear in if no lights are on?
Landing gear is ‘up’ and doors closed and locked
The light is out if the particular landing gear is ‘up’ and the doors are closed and locked. The cockpit crew is not distracted by an unnecessary warning.
How are wheels made up?
Rims are made of aluminium alloys and are of the split type hubs (2 pieces)
What type of bearings are used in aircraft wheels?
Conical roller bearings
What material are tyres made from and why?
Aircraft tyres are made of natural rubber.
Natural rubber conducts heat better than synthetic rubber.
What is the purpose of a wheel fuse?
To melt the plug core at 145^C allowing nitrogen to escape from the tire before pressure builds up due to heat causing a sudden decompression or explosion.
List the components in a braking system?
How is an aircraft steered on the ground?
Castoring system - Differential use of the brakes (used for small aircraft eg cessna)
Tiller system - Used for steep turns of large commercial aircraft
Rudder - Used for minor turning corrections at slow speed on runway etc
What happens to kinetic energy when the aircraft lands?
Upon landing, an oleo shock absorber converts kinetic energy into heat energy and part into a pressure increase.
What is wheel base?
The distance between the centre point of the nose or tail gear to the wheel axles of the main landing gear
What is wheel track?
The distance between the far right and far left landing main landing gear.
What gas is commonly used in landing gear struts?
Nitrogen gas is commonly used in landing gear struts
(compressed air??)
On landing, how is fluid flow within the strut slowed down?
Before landing, the small end of the tapered metering pin is in the orifice. Upon landing, as the strut collapses, the metering pin is forced up and it’s tapered shape gradually decreases the area of the orifice slowing down fluid flow.
What assists in preventing the aircraft from bouncing after landing?
The flapper valve closes after landing to prevent fluid flowing back into the piston which would cause a bounce. The fluid must flow through the small holes in the snubber tube to get back into the piston.
What ensures that the nose landing gear wheels are in the correct position after take-off?
Centring cams in the inner and outer struts. After take-off, as the strut extends, the centring cams force the nose wheel straight ahead.
What component(s) ensures that the process of landing gear extension and retraction occurs in the correct order?
Sequence valves ensure the correct sequence of operation occurs with the hydraulic components, landing gear door opening and closing, up-lock and down-lock mechanism.
What component ensures that the main landing gear is at the correct angle to fit properly in the wheel well?
A trim cylinder or tilt cylinder ensures the bogie beam is at the correct angle to fit into the wheel well.
What positions can the landing gear lever be placed?
The landing gear lever can be in the ‘’up’’, ‘’oft’’ (neutral) or the ‘’down’’ position.
How are aircraft wheel rims constructed?
Aircraft Wheel Rims are constructed from aluminium alloys in two parts (split hub) connected by bolts and nuts. An O-ring seal between the two parts prevents loss of nitrogen.
Main gear wheels in addition have splines which move the brake unit rotor vanes when the wheels are spinning. Ventilation holes and a heat shield aim to minimise heat transfer from the brake units.
What type of wheel bearings are used on aircraft wheel assemblies?
Conical roller bearings are used on aircraft wheel assemblies due to high radial and axial loads.
What colour light appears on the flight deck when the landing gear is down and locked?
A green light appears on the flight deck indicating the landing gear is down and locked.
The flapper valve is a _____ ______ _____ _____
One way check valve
What component reduces nose wheel vibration on take-off and landing?
A shimmy damper between the nose wheel cylinder and piston which transfers hydraulic fluid from one side of the piston to the other through a bleed hole.
(Transfer of this fluid which absorbs vibration)
What is toe-in and toe-out?
Toe-in is where the main landing gear wheels are closer together as you move forward. In this case, the wheels tend to try to move together.
Toe-out is where the main landing gear wheels are further apart as you move forward. The wheels tend to try to move farther apart.
Either condition is allowed within a certain tolerance specified by the Manufacturer in the AMM.
What is wheel camber?
Wheel camber is the amount an aircraft wheel is tilted from the vertical position. If it tilts outward from it’s strut, it’s positive camber and if it tilts towards it’s strut, it’s negative camber.
What is the most common type of ply used on modern commercial aircraft tyres?
Nylon
What is a shuttle valve used for?
A shuttle valve is used to direct either normal system hydraulic pressure or emergency compressed air into an actuator cylinder as a backup means of actuating the landing gear or applying brakes in the event of hydraulic pressure loss.
What is aquaplaning/hydroplaning?
Aquaplaning/Hydroplaning occurs on water-covered runways where a layer of water is between the tire and runway reducing traction. When brakes are applied, the tires will lockup due to the low surface friction and skid on the water surface
What do we call a multiple axle landing gear?
Bogie Beam or Axle carrier
What component attaches the inner cylinder to the outer cylinder?
Torque Link
What type of bearings are used in wheels?
Conical Roller bearings
What is meant by the concepts: Wheel base and wheel track?
Wheel base is the distance between the centre point of the nose gear or tail gear and main landing gear
Wheel track is the distance between the far right and far left main landing gear.
In what part of the landing gear do you find fluid and nitrogen?
Inner strut contains fluid (oil)
Outer strut contains compressed air (nitrogen)
What is the function of the centering cams?
Before being retracted into the wheel well, the nose gear strut is fully extended and the centering cams ensure it is centered.
The opposition to the landing impact is gradually increased in an oleo shock strut by a ________________ decreasing he size of the orifice
tapered-metering pin
Rebound is minimized with an oleo shock strut by restricting the flow of oil by the closing of the _____ valve
flapper
If the top of the main wheel of an airplane tilts outward, the wheel has a ______ camber
(positive or negative)
positive
The wheels of an airplane equipped with an oleo shock absorber are aligned by adding shims between the ___________
torque link arms
The wheels of an airplane equipped with an oleo shock absorber are aligned by adding shims between the ____________
torque link arms
The emergency brake system of a jet transport airplane uses _______ to actuate the brakes
nitrogen (compressed air via shuttle valves)
Most of the wheels used on modern aircraft are of the ________ type
(single-piece or two-piece)
Two-piece type
Wheels on modern high-performance airplanes are prevented from exploding from heat generated in the brakes by _________ installed in the inboard wheel half.
Fusible plugs
The bundles of high-strength steel wires that are molded into a tire are called the ______
beads
Nose wheel tires used on jet airplanes with engines mounted on the aft fuselage have a _____ or _____ molded into their outer sidewalls
Deflector or “chine” (N not M)
(deflects water sideways instead of rearwards into engine)
What does Shimmy mean?
Undesirable unsteadiness of the nose wheels is called “shimmying”.
What is the function of the carcass and how is it constructed?
The carcass serves to absorb the pressures on the tyre.
The carcass
consists of several nylon layers. Every layer (ply) consists of a large number of diagonal or radial threads. The threads of two consecutive layers
are at an angle to each other (90^C)
What kind of wheel rims are used?
Most aircraft have wheel rims that consist of two parts (split hub)
The two halves are connected to each other by means of
bolts and nuts. In addition, an O-ring seal has been installed between the two halves of the wheel rim to prevent loss of nitrogen from the “tubeless” tyres.
What are the main parts of an aircraft tyre?
How are aircraft wheels made up?
(components)
Wheel Rim (2 piece split hub)
Tire consisting of:
Thread
Carcass (cord body)
Shoulder
Side wall
Bead
Will auto braking work if the anti-skid system is inop?
Yes, the auto-breaking system will only trip itself off if:
- Thrust levers are pushed out of idle position
- the brake pedals are operated
- the speed of the aircraft has dropped below a certain value
- if there is a system malfunction
