Landing Gear Flashcards
functions to provide a means of maneuvering the aircraft on the ground
landing gear
functions to support the aircraft at a convenient height to give clearance for propellers and to facilitate loading
landing gear
functions to absorb the kinetic energy of landing and provide a means of controlling deceleration
landing gear
Landing Gear Layout
tricycle layout, tailwheel or taildragger
nose wheel unit forward of two main gear units
tricycle layout
tail wheel behind the main wheels
tailwheel or taildragger
landing gear type fitted for slow, light aircraft, and some larger aircraft on which simplicity is of prime importance
fixed (non retractable) landing gear
The reduced performance caused by the drag of the landing gear (fixed landing gear) during flight is offset by the _______, ________, and ________.
simplicity, reduced maintenance, low initial cost
landing gear type utilized for higher performance aircraft because of more progressive drag; retracted into wings or fuselage during flight
retractable landing gear
downsides of retractable landing gear
increased weight, greater complication, additional maintenance
3 main types of fixed landing gear
spring steel leg, rubber cord (shock absorber), oleo-pneumatic struts
usually employed at the main undercarriage positions
spring steel legs
A spring steel leg consists of a ______ or tapered spring steel.
tube
In a spring steel legs, the upper end is attached by _____ to the _______ and the lower end terminating in the ______ on which the wheel and brake are assembled.
bolts, fuselage, axle
type of fixed landing gear used as a shock-absorber
rubber cord
In a rubber cord, the undercarriage is usually in the form of ________.
tubular struts
The undercarriage of a rubber cord is designed and installed so that the landing force is directed against a number of turns of rubber in the form of a ______ or ______.
grommet, loop
Some fixed main undercarriages and most fixed nose undercarriages are fitted with this type of fixed landing gear. What is this type of fixed landing gear?
oleo-pneumatic struts
In oleo-pneumatic struts, the design of individual struts _____ considerably but the operating principle is _____ for all.
varies, same
One point worthy of consideration in oleo-pneumatic struts is the fitting of _____ to oleo-pneumatic strut.
spats
an aerodynamic fairing which may be required to minimize the drag of the landing gear structure
spats
A simple oleo-pneumatic strut consists of _________, one free to slide inside the other.
two concentric cylinders
The cylinders in a simple oleo-pneumatic strut are filled with ________ and _____.
hydraulic fluid, gas
The hydraulic fluid and gas in the cylinders of oleo-pneumatic struts are kept apart by a _______.
separator piston
In a simple oleo-pneumatic strut, the outer or upper cylinder is attached to the ________.
airframe structure
In a simple oleo-pneumatic strut, the outer or upper cylinder houses the _______ and a _______.
inner or lower cylinder, piston assembly
In an oleo-pneumatic strut, these are connected to the bottom of the inner cylinder. What are these?
wheels, axle
In an oleo-pneumatic strut, the inner cylinder is ______ and move up and down within the outer cylinder.
free to rotate
In an oleo-pneumatic strut, _______ and up and down movement is limited by the _______.
rotary movement, torque links
In an oleo-pneumatic strut, what connects the inner and outer cylinders together?
torque links
What are other terms for torque links?
torsion or scissor links
Landing gear is subject to torsion loads during ground maneuvering and these loads are taken by the ________.
torque links
The ______ the radius of turn, the ______ will be the load felt by the torque links so all turns should be made as wide as possible.
smaller, greater
In an oleo-pneumatic strut, the are on the outer cylinder is filled with ______.
hydraulic fluid
In an oleo-pneumatic strut, the are on the inner cylinder is filled with _______ which may be _______ or _______.
compressed gas, air, nitrogen
It is a free-floating piston which keeps the fluid and gas apart.
separator piston
The _____ supports the weight of the aircraft on the ground, cushions bump during taxiing, and absorbs the _____ on landing.
gas, shock
Its purpose is to dampen oscillations and control the rate of compression and extension of the cylinders.
hydraulic fluid
In an oleo-pneumatic strut, the purpose of the hydraulic fluid is to _________ and control the rate of __________ of the cylinders.
dampen oscillations, compression and extension
The piston connected to the lower cylinder has _____ in it which restricts the flow of fluid through the piston, thus, dampening the movement between the cylinders.
holes
fitted to the lower cylinder piston assembly
flutter valve
consists of a free-floating circular plate with a large central hole
flutter valve
free to move up and down within its housing
flutter valve
In an oleo-pneumatic strut, on the top of the inner cylinder, there is a ________ plus a series of holes around the perimeter.
small central orifice
If the fluid is flowing upwards, the strut is ______.
extending
If the fluid is flowing downwards, the strut is ______.
contracting
If fluid is flowing ________, the plate will be pushed up with it, blocking off the outer holes and allowing a limited flow only through the central orifice.
upwards
If fluid is flowing ________, then the plate will be pushed down allowing a greater flow of fluid through all of the holes.
downwards
Flutter valve then limits the rate of movement, more restriction when _______, less restriction when ________.
extending, contracting
Determine the scenario:
the gas pressure will support the weight of the aircraft with the lower cylinder approximately on the midway of its stroke
Aircraft stationary on the ground
Determine the scenario:
cushioned by the gas pressure and dampened by the limited flow of fluid through the orifice
bumps during taxiing
Determine the scenario:
gas pressure will cause the lower part of the leg to extend to its fullest extent
takeoff
Determine the scenario:
strut shortens, and fluid is forced through the flutter valve
landing
As the downward force of the landing ______, the gas pressure acts as a spring and extends the strut.
decreases
The flutter valve plate will move with the fluid flow blocking off the outer holes and further reducing the speed of upward movement of the upper cylinder, thus, helping to prevent a ______ on landing.
bounce
Wheels to Leg Construction
fork, half fork, cantilever, dual wheel, multiwheel (bogie connected)
Employed to improve aircraft performance by reducing drag
retractable landing gear
In a retractable landing gear, it is provided to ensure that each undercarriage is locked securely in the retracted and extended positions.
mechanical locks
________ are installed by which the landing gear can be extended in the event of failure of the power source.
manual means
In a retractable landing gear, systems are provided to prevent ________ with the aircraft on the ground.
retraction
_________ are installed to guard against landing with the landing gear retracted.
warning devices
The geometrical arrangement and physical location of undercarriage units on aircraft is ___________.
by no means standard
The type, size, and position are decided at the _________, having already taken into account the many factors that must be considered.
design stage
the two main undercarriage units are positioned just aft of the center of gravity in this layout
tricycle layout
Tricycle layout support up to __% of the aircraft’s weight and all initial landing shocks.
90
In a retractable landing gear, the leg is attached to the wing spars by a ___________ on which the leg is free to rotate laterally.
cylindrical beam or trunnion
In a retractable landing gear, the leg is attached to the _______ by a cylindrical beam or trunnion on which the leg is free to rotate laterally.
wing spars
In a retractable landing gear, the upper part of the leg forms the ______ cylinder of the oleo-pneumatic strut.
outer
The strut inner cylinder is connected to the _______ or _______.
wheel bogie, truck beam
It is able to pivot about its central point in a controlled way.
truck beam
There is an _____ connected to a pair of _________ at each end of the truck beam.
axle, break wheels
The _________ prevent rotation between the shock strut inner and outer cylinders without affecting their reciprocating action during normal operation of the strut.
wing gear torque links
The ______ supports the leg in fore and aft direction.
drag strut
The __________ support the leg laterally.
upper and lower side struts
The upper and lower side struts fold out when the gear is lowered and are then held in place by the _______ which also folds out during extension.
jury strut
It is pulled over center by the down lock actuator geometrically locking the gear down.
jury strut
The jury strut is pulled over center by the _______ geometrically locking the gear down.
down lock actuator
If the gear is lowered without hydraulic power, then the over centering action will be performed by an internal spring in the _________.
down lock actuator
With no ______ available, provision has to be made for locking the undercarriage up and down.
geometric lock
Depending on wheel layout, each wheel may require its own ________, and possibly even a steering motor.
shock absorber unit
Depending on wheel layout, each wheel may require its own shock absorber unit, and possibly even a _______.
steering motor
_________ to the undercarriage in flight allows manual lowering of the undercarriage in emergency.
ease of access
Loads sustained by the landing gear
- compressive loads
- rearward bending loads
- side loads
- forward loads
- torsional loads
Determine the load:
landing and static on ground
compressive loads
Determine the load:
during breaking
rearward bending loads
Determine the load:
during cross wind landings, takeoffs, and taxiing
side loads
Determine the load:
during push back
forward loads
Determine the load:
ground maneuvering
torsional loads
It is usually a lighter structure than a main unit since it carries less weight and is usually subject only to direct compression loads.
Nose Landing Gear
It carries the attachment for the towing equipment and so must withstand shear loads as well.
Nose Landing Gear
The design of a nose landing gear is complicated by several requirements which are:
- castoring
- self-centering
- steering
- anti-shimmy
- can withstand shear loads
the ability of the nose wheel to turn to either side in response to the results of differential braking, thrust, or aerodynamic forces on the rudder, and to return back to its central position when the forces are removed
castoring
enables the aircraft to be maneuvered about the airfield
castoring
___________ of the nose wheel is essential prior to landing gear retraction.
automatic self centering
If the nose gear is not in a central position prior to its retraction, the restricted space available for its stowage will not be sufficient and severe damage may be caused to the aircraft structure as the hydraulic system forces the gear upwards.
wala lang, intindihin mo lang, pero sa nose wheel self-centering siya
achieved by either a cam system or by hydraulic power through steering actuators
centering
A method of steering is required to enable the pilot to maneuver the aircraft safely on the ground. Early methods involved the use of ________.
differential breaking
_________ using hydraulic systems are now common to most large commercial aircraft, allowing the engines to be set at the minimum thrust for taxiing, thereby saving fuel, an important consideration with large jet engines.
powered steering
A hydraulically powered system may include a cockpit __________, a _________ steering cylinders to hold the nose gear, and a ______________ to hold the nose wheel at the selected angle.
steering wheel or tiller, control valve, mechanical feedback device
Steering is controlled depending on the type of aircraft by either the tiller or the operation of the __________.
rudder pedals
In hydraulically controlled nosewheel steering systems, the operating pressure is derived from the _________.
aircraft hydraulic system
Steering is only available when the gear is selected down. What gear?
landing gear
There are two ________ which steer the nose gear.
steering actuators
In some aircraft, a limited emergency supply may be provided by a __________.
hydraulic accumulator
The _______ in the pipelines between the steering actuators provide dampening for the steering operation and help to prevent nose wheel shimmy.
restrictors
The steering wheel or tiller is mechanically linked to the ________.
steering control valve
The _________ is mechanically linked to the steering control valve.
steering wheel or tiller
A _________ from the nose undercarriage gradually resets the control valve as the nose wheel turns.
follow-up linkage
When the tiller is turned, it moves the ________ away from its central position.
control valve
When the nosewheel reaches the selected angle, the _________ will centralize the control valve shutting off a fluid to the actuators.
follow-up linkage
fitted between the two sides of the steering actuators
safety bypass valve
normally held closed by hydraulic pressure
safety bypass valve
purpose is to allow the nosewheel to castor if there is a hydraulic failure
safety bypass valve
If the hydraulic system should fail, the spring will push open the valve allowing fluid to flow freely between the actuators thus allowing the nose wheel to _______.
castor
Some systems have the facility to bypass the system during _______.
towing operations
When operated, it opens the steering bypass valve.
bypass lever
When the bypass lever is operated by ground operator at the nose gear location, it opens the valve allowing fluid to flow freely between the _______.
steering actuators
A ______ with a flag attached is fitted to hold the lever in the valve open position.
bypass pin
A bypass pin with a flag attached is fitted to hold the lever in the valve open position. The ______ can now tow the aircraft and turn the nosewheel as necessary.
tractor
Large aircraft with ______ main gears have a problem with the main gears sliding sideways in turns.
multiwheel
problem with the main gears sliding sideways in turns; can quickly damage tires
scrubbing
o help improve the turning circle and reduce tire scrubbing, some aircraft have ________.
steerable body gear
operates automatically in the opposite direction to the nose gear when the nose gear steering is operated
steerable body gear
Due to the flexibility of tire sidewalls, an unstable rapid sinusoidal oscillation or vibration can happen into the nose undercarriage. What is the phenomenon called?
shimmy
Worn or broken torque links, wear in the wheel bearings, and uneven tire brushes can all increase the tendency to _______.
shimmy
_________ especially at high speeds can set up vibrations throughout the aircraft and can be dangerous.
excessive shimmy
Best Ways to Keep Shimmy to a Minimum
- maintain landing gear correctly
- replacing worn-out parts
- maintaining correct tire pressures
A hydraulic or ________ can be attached between the upper and lower oleo-pneumatic strut cylinders.
spring shimmy damper
Many larger aircraft use _______ to help reduce shimmy while _______ have been found to be effective in minimizing tail wheel shimmy.
double nose wheels, twin contact tires
It is used to provide a positive indication to the crew of the operation of the locks and the position of the landing gear.
electrical indicating system
The indicating system usually consists of _______ or _________ monitoring the up and down locks.
micro switches, proximity sensors
These make or break electrical circuits when the locks operate causing indications to change on the landing gear position indicator on the instrument panel.
electrical indicating system
________are simple mechanically operated electrical switches which are operated by a _______ when the gear reaches the required position.
micro switches, striker plate
______ are electronic devices with no moving parts.
proximity switches
Each proximity switch consists of two components which are:
sensor, target
It is based on the proximity of the target and the sensor.
signal
The sensors are usually duplicated for _________.
safety reasons
________ may also be provided in some aircraft to show that the landing gear is down and locked if the electrical indicating system fails for the main gear.
mechanical indicators
These are often just buttons which pop up on the top of the wing when the gear is locked down.
mechanical indicators
The nose gear will often have some sort of ________ in the cockpit floor through which the down lock can be seen.
periscopic viewer
Some aircraft don’t have mechanical indicators, instead they have ____________.
duplicated electrical down lock sensors
is displayed when the undercarriage is locked down
green light
is displayed when the undercarriage is in transit
red light
are visible when the undercarriage is locked up
no lights
are usually duplicated to avoid the possibility of false indications as a result of bulb failures
bulbs
Many large aircraft also have ________ to indicate that the hydraulically operated doors are closed and locked.
main gear door lock indicators
color of lights of main gear door lock indicators
red or amber
The gear actuator and door actuator are _______.
double acting unbalanced actuators
The gear is locked down by a ________.
geometric lock mechanism
______ is hydraulically opened and closed.
door
Door is ______ when the gear is locked up and _______ when the gear is locked down.
closed, opened
It is a disagreement light; it illuminates at any time the gear and the lever are in disagreement so when the gear is selected up, the first thing that happens is that it illuminates. However, the gear is still locked down so the _______ remains.
gear red-light, green gear down light
The _________ controlled by the gear lever will send _________ to the door actuator. The door now begins to open, and the door open light illuminates.
selector valve, pressure fluid
The ________ will begin to retract breaking the geometric lock, the gear is now unlocked so it’s green gear down light will go out.
down lock actuator
The gear actuator can now raise the gear when the gear is fully up the _____.
up lock
Once the gear is locked up the _______ will go out.
red gear light
Valve will direct the hydraulic fluid to the ________ and the door closes.
door actuator
Once door is fully closed, the _________ will go out with the gear up and doors closed. There will be _____ lights on the indicator.
amber door open light, no
Once the gear is up and locked and the door is closed, the gear lever is placed to the ________ leaving the gear unpressurized for the period of the cruise so extending the life of the landing gear components and preventing unwanted leakage of hydraulic fluid.
off position
The sequence when the gear is selected down is basically the __________.
up sequence in reverse
When the lever is selected down the red gear light comes on to indicate a ______ between the lever and the gear.
disagreement
When the door is fully open, the valve will redirect the hydraulic fluid to the ________ and the _______. The gear actuator will now lower the gear assisted by the weight of the gear.
gear up lock actuator, gear actuator
To control the speed of lowering, the returned fluid from the gear actuator passes through a _________ in the restricted flow direction.
one-way restrictive valve
When the gear approaches the fully down position, a powerful spring in the lockdown actuator will push the geometric lock on the center, locking the gear ______. Red gear light goes out and the green light comes on.
down
Once the gear is locked down, the door sequence valve directs fluid to the _______, door closes, and the door light ______.
door actuator, goes out
When the gear is locked down, there are green down pointing triangles on both the undercarriage indicator and on the ________.
Electronic Centralized Aircraft Monitor (ECAM) screen
What model of aircraft equips an ECAM and what does ECAM stand for?
Airbus A320, Electronic Centralized Aircraft Monitor
When the gear is neither locked up nor down, the triangles on the ECAM screen are ____ and _______ is displayed on the landing gear indicator.
red, unlocked
When the gear is up and locked, the displays on an ECAM screen are ______.
blank
Door positions symbols on an ECAM screen are ______ when the doors are locked and closed, and _____, when they are not.
green, amber
