Topic 3: Aircraft Landing Gear Flashcards
The functions of the landing gear are:
- To provide a means of maneuvering
the aircraft on the ground. - To support the aircraft at a convenient
height to give clearance for propellers
and to facilitate loading. - To absorb the kinetic energy of landing
and provide a means of controlling
deceleration.
this provides a means of maneuvering
the aircraft on the ground.
landing gear
this supports the aircraft at a convenient
height to give clearance for propellers
and to facilitate loading.
landing gear
this absorbs the kinetic energy of landing
and provide a means of controlling
deceleration.
landing gear
landing gear layout
- tricycle layout
- tailwheel or taildragger
this landing gear layout has its nose wheel unit forward of two main gear units.
tricycle layout
this landing gear layout has a tail wheel behind the main wheels.
tailwheel or taildragger
landing gear types:
- fixed (non-retractable) landing gear
- retractable landing gear
With slow, light aircraft, and some larger
aircraft on which simplicity is of prime
importance, this is often fitted.
fixed (non-retractable) landing
gear
In this landing gear type, the reduced performance caused by the drag of the landing gear during flight is offset by the simplicity, reduced maintenance, and low initial cost.
fixed (non-retractable) landing gear
With higher performance aircraft, drag
becomes progressively more important, and this is retracted into the wings or fuselage during flight.
retractable landing gear
Its penalties include increased weight, greater
complication, and additional maintenance.
retractable landing gear
3 main types of fixed landing gear:
- spring steel leg
- rubber cord (shock absorber)
- oleo-pneumatic struts
these are usually employed at the main
undercarriage positions.
spring steel legs
The leg consists of a tube, or strip of
tapered spring steel.
spring steel leg
The upper end is attached by bolts to the fuselage and the lower end terminating in an axle on which the wheel and brake are
assembled.
spring steel leg
when used as a shock-absorber, the undercarriage is usually in the form of tubular struts, designed and installed so that the landing force is directed against a number of turns of rubber in the form of a grommet or loop.
rubber cord
some fixed main undercarriages, and most fixed nose undercarriages, are fitted with this
oleo-pneumatic shock absorber strut
one point worthy of consideration is the fitting of spats to this.
oleo-pneumatic strut
are an aerodynamic fairing which may be required to minimize the drag of the landing gear structure.
spats
consists of two concentric cylinders, one free to slide inside the other.
a simple oleo-pneumatic strut
Its cylinders are filled with hydraulic fluid and gas which are kept apart by a separator piston.
oleo-pneumatic strut
its outer or upper cylinder is attached to the airframe structure and houses the inner or lower cylinder and a piston assembly.
oleo-pneumatic strut
its wheels and axle are connected to the bottom of the inner cylinder
oleo-pneumatic strut
Its inner cylinder is free to rotate and move up and down within the outer cylinder
oleo-pneumatic strut
rotary movement and up and down movement is limited by this which connect the inner and outer cylinders together
torque links
also called torsion or scissor links
torque links
landing gear is subjected to torsion loads during ground maneuvering and these loads are taken by the _____________
torque links
landing gear is subject to this during ground maneuvering
torsion loads
the smaller the radius of turn, the greater will be the load felt by the ___________ so all turns should be made as wide as possible.
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 the operation of oleo-pneumatic struts, the area on the outer cylinder is filled with __________ and the area on the inner cylinder is filled with compressed gas which may be either __________ or ___________.
hydraulic fluid; air; nitrogen
in the operation of oleo-pneumatic struts, this is a free-floating piston which keeps the fluid and gas apart.
separator piston
in the operation of oleo-pneumatic struts, the _________ supports the _________ of the aircraft on the ground, __________ during taxiing, and absorbs the ___________ on landing.
gas; weight; cushion bumps; shock
in the operation of oleo-pneumatic struts, its purpose is to dampen oscillations and control the rate of compression and extension of the cylinders.
hydraulic fluid
in the operation of oleo-pneumatic struts, the _________ connected to the lower cylinder has _________ in it which restricts the flow of fluid through the piston, thus, dampening the movement between the cylinders.
piston; holes
in the operation of oleo-pneumatic struts, this component is fitted to the lower cylinder piston assembly.
flutter valve
in the operation of oleo-pneumatic struts, this consists of a free-floating circular plate with a large central hole and is free to move up and down within its housing.
flutter valve
in the operation of oleo-pneumatic struts, on the top of the inner cylinder, there is a small ________ plus a ________ around the perimeter
central orifice; series of holes
when this happens in the operation of oleo-pneumatic struts, the plate will be pushed up with it, blocking off the outer holes and allowing a limited flow only through the central orifice.
fluid is flowing upwards (strut extending)
when this happens in the operation of oleo-pneumatic struts, the plate will be pushed down allowing a greater flow of fluid through all of the holes
fluid is flowing downwards (strut contracting)
in the operation of oleo-pneumatic struts, the ________ limits the rate of movement, ________ restriction when extending, and ________ restriction when contracting
flutter valve; more; less
when an aircraft is stationary on the ground, the _______ will support the weight of the aircraft with the lower cylinder approximately on the _______ of its stroke.
gas pressure; midway
during taxiing, bumps are cushioned by the _______ and dampened by the _______ through the orifice.
gas pressure; limited flow of fluid
during takeoff, this will cause the lower part of the leg to extend to its fullest extent
gas pressure
during landing, the _______ shortens and the _______ is forced through the flutter valve.
strut; fluid
as the downward force of the landing decreases, this acts as a spring and extends the strut
gas pressure
as the downward force of the landing decreases, the _______ 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 bounce on landing.
flutter valve plate
wheels to leg construction:
- fork
- half fork
- cantilever
- dual wheel
- multiwheel (bogie connected)
employed to improve aircraft performance by reducing drag
retractable landing gear
also provided with mechanical locks to ensure that each undercarriage is locked securely in the retracted and extended positions.
retractable landing gear
retractable landing gear is also provided with _________ to ensure that each undercarriage is locked securely in the retracted and extended positions.
mechanical locks
this also has devices present to indicate to the crew the position of each undercarriage
retractable landing gear
manual means are installed by which it can be extended in the event of failure of the power source.
retractable landing gear
systems are provided to this to prevent retraction with the aircraft on the ground.
retractable landing gear
it has warning devices installed to guard against landing with the landing gear retracted.
retractable landing gear
in the designing and construction of retractable landing gear, the ________ and ________ of undercarriage units on aircraft is by no means standard.
geometrical arrangement and physical location
in the designing and construction of retractable landing gear, the type, size and position are decided at the _______, having already taken into account the many factors that must be considered.
design stage
in the designing and construction of retractable landing gear, most aircraft use the ________, where the two main undercarriage units are positioned just aft of the center of gravity and support up to ________ of the aircraft’s weight and all initial landing shocks.
tricycle layout; 90%
in the designing and construction of retractable landing gear, the leg is attached to the wing spars by a ________ or ________ on which the leg is free to rotate laterally.
cylindrical beam; trunnion
in the designing and construction of retractable landing gear, the upper part of the leg forms the outer cylinder of the _______.
oleo-pneumatic strut
in the designing and construction of retractable landing gear, the strut inner cylinder is connected to the _______ or _______.
wheel bogie; truck beam
The ________ is able to pivot about its central point in a controlled way. There is an ________ connected to a pair of break wheels at each end of the truck beam.
truck beam; axle
in the designing and construction of retractable landing gear, the wing gear ________ prevent rotation between the shock strut inner and outer cylinders without affecting their reciprocating action during normal operation of the strut.
torque links
in the designing and construction of retractable landing gear, this supports the leg in fore and aft direction
drag strut
in the designing and construction of retractable landing gear, the ________ support the leg laterally. They fold out when the gear is lowered and are then held in place by the ________ which also folds out during extension.
upper and lower side struts; jury strut
in the designing and construction of retractable landing gear, this is pulled over center by the down lock actuator geometrically locking the gear down.
jury strut
in the designing and construction of retractable landing gear, if the gear is lowered without hydraulic power, then the over centering action will be performed by an internal spring in the ________.
downlock actuator
For aircraft with the undercarriage built into the fuselage (fuselage mounted landing gear), the requirements are basically the same as those for the wing mounted landing gear, except that:
- With no geometric lock available, provision has to be made for locking the undercarriage up and down.
- Depending on wheel layout, each wheel may require its own shock absorber unit, and possibly even a steering motor.
- Ease of access to the undercarriage in flight allows manual lowering of the undercarriage in emergency.
for a fuselage mounted landing gear with no geometric lock available, ________ has
to be made for locking the undercarriage up
and down. Depending on wheel layout, each wheel may require its own _________, and possibly even a ________.
Ease of access to the undercarriage in flight
allows _________ in emergency.
provision; shock absorber unit; steering motor; manual lowering of undercarriage
loads sustained by the landing gear:
- Compressive loads
- Rearward bending loads
- Side loads
- Forward loads
- Torsional loads
loads sustained by the landing gear during landing and static on ground
compressive loads
loads sustained by the landing gear during breaking
rearward bending loads
loads sustained by the landing gear during cross wind landings, takeoffs, and taxiing
side loads
loads sustained by the landing gear during push back
forward loads
loads sustained by the landing gear during 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 does, however, carry the attachment for the towing equipment and so must withstand shear loads as well.
nose landing gear
Its design is complicated by several requirements:
1. Castoring
2. Self-centering
3. Steering
4. Anti-shimmy
5. Can withstand shear loads
nose landing gear
the design of nose landing gear is complicated by several requirements:
- 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
nose wheel castoring
_________ of the nose wheel is essential prior to landing gear retraction.
automatic self-centering
If the _________ 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.
nose gear
achieved by either a cam system or by hydraulic power through steering actuators.
centering
this is required to enable the pilot to maneuver the aircraft safely on the ground. Early methods involved the use of differential braking.
a method of steering
using hydraulic systems, this is 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
In nose wheel steering, a hydraulically powered system may include a ________, a ________ to hold the nose gear, and a _________ to hold the nose wheel at the selected angle.
steering wheel or tiller; control valve steering cylinders; mechanical feedback device
In nose wheel steering, _________ is controlled depending on the type of aircraft by either the ________ or the operation of the ________.
steering; tiller; rudder pedals
In hydraulically controlled nosewheel steering systems, the operating pressure is derived from the ________.
aircraft hydraulic system
how many steering actuators steer the nose gear in nose wheel steering?
2
In nose wheel steering in some aircraft, a limited emergency supply may be provided by a ________.
hydraulic accumulator
In nose wheel steering the ________ in the pipelines between the steering actuators provide ________ for the steering operation and help to prevent nose wheel ________.
restrictors; dampening; shimmy
In nose wheel steering, the ________ is mechanically linked to the _________. A ______
from the nose undercarriage gradually
resets the control valve as the nose
wheel turns.
steering wheel or tiller; steering
control valve; follow-up linkage
In nose wheel steering, when the nosewheel reaches the selected angle, the ________ will centralize the control valve shutting off a fluid to the actuators.
follow-up linkage
In nose wheel steering, there is a _______ fitted between the two sides of the ________. It is normally held closed by
________.
safety bypass valve; steering actuators; hydraulic pressure
In nose wheel steering, the purpose of the ________ is to allow the nosewheel to castor if there is a hydraulic failure.
safety bypass valve
In nose wheel steering, if the hydraulic system should fail, the ________ will push open the valve allowing fluid to flow freely between the actuators thus allowing the nose wheel to castor.
spring
In nose wheel steering, some systems have the facility to bypass the system during ________.
towing operations
In nose wheel steering, some systems employ a ________ which when operated opens the steering bypass valve. When the _______ is operated by ground operator at the nose gear location, it opens the valve allowing fluid to flow freely between the steering actuators.
bypass lever; lever
In nose wheel steering, a ________ with a flag attached is fitted to hold the lever in the valve
open position. The tractor can now tow the aircraft and turn the nosewheel as
necessary.
bypass pin
Large aircraft with multiwheel main gears have a problem with the main gears sliding sideways in turns. This is known as ________ and can quickly damage tires.
scrubbing
To help improve the turning circle and reduce tire scrubbing in main gear steering, some aircraft have ________ which 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 known as _________ can happen into
the nose undercarriage.
shimmy
Worn or broken torque links, wear in the
wheel bearings, and uneven tire brushes can all increase the tendency to ________.
shimmy
Worn or broken _________, wear in the
__________, and uneven _________ can all increase the tendency to shimmy.
torque links; wheel bearings; tire brushes
Excessive shimmy especially at high speeds can set up _________ throughout the aircraft and can be dangerous.
vibrations
The best ways to keep shimmy to a minimum are by:
- maintaining the landing gear correctly;
- replacing worn-out parts; and
- maintaining correct tire pressures.
Many nose wheels are still prone to shimmy and there are a number of methods used to try and reduce its effects. _________ in the form of restrictors can be provided across the steering jack.
hydraulic damping
A __________ can be attached between the upper and lower oleo pneumatic strut cylinders.
hydraulic or 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
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
This system usually consists of micro switches or proximity sensors monitoring the up and down locks.
indicating system
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.
micro switches or proximity sensors
simple mechanically operated electrical
switches which are operated by a striker plate when the gear reaches the required position.
micro switches
electronic devices with no moving parts.
proximity switches
in an indicating system, each proximity switch consists of two components:
- sensor
- target
in an indicating system, this is based on the proximity of the target and the sensor.
signal
in an indicating system, these are usually duplicated for safety reasons.
sensors
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
this will often have some sort of periscopic viewer in the cockpit floor through which the down lock can be seen.
nose gear
Some aircraft don’t have mechanical indicators, instead they have _________.
duplicated electrical down lock sensors
in an indicating system, this is displayed when the undercarriage is locked down.
green light
in an indicating system, this is displayed when the undercarriage is in transit.
red light
when the undercarriage is locked up, _________ are visible.
no lights
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. These lights may be _________.
main gear door lock indicators; red or amber
in a landing gear system hydraulics operation, the gear actuator or door actuator are ________.
double acting unbalanced actuators
in a landing gear system hydraulics operation, the gear is locked down by a ________.
geometric lock mechanism
in a landing gear system hydraulics operation, the _________ is hydraulically opened and closed. It is ________ when the gear is locked up and _________ when the gear is locked down.
door; closed; opened
Gear lever ________, gear ________, green gear down ________, door open ________.
down position; locked down; light on; light out
________ down position, ________ locked
down, ________ light on, ________
light out.
gear lever; gear; green gear down; door open
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 this illuminating.
gear red light
in a landing gear system hydraulics operation, the ________ controlled by the gear lever will send pressure fluid to the door actuator. The _________ now begins to open, and the ________ illuminates.
selector valve; door; door open light
in a landing gear system hydraulics operation, the ________ will begin to retract breaking the geometric lock the ________ is now unlocked so its ________ will go out.
down lock actuator; gear; green gear down light
in a landing gear system hydraulics operation, this can now raise the gear when the gear is fully up the up lock.
gear actuator
in a landing gear system hydraulics operation, once the gear is locked up, the _________ will go out.
red gear light
in a landing gear system hydraulics operation, the ________ will direct hydraulic fluid to the _________ and the ________ closes.
valve; door actuator; door
once the door is fully closed in a landing gear system hydraulics operation, the ________ will go out with the ________ up and the ________ closed. There will be ________ on the indicator.
amber door open light; gear; doors; no lights
Once the gear is up and locked and the
door is closed in a landing gear system hydraulics operation, the _________ 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.
gear lever; off position
in a landing gear systems hydraulics operation, the sequence when the gear is selected down is basically the __________.
up sequence in reverse
in a landing gear system hydraulics operation, when the lever is selected down the _________ comes on to indicate a disagreement between the lever and the gear.
red gear light
in a landing gear system hydraulics operation, fluid is directed to the _________. _________ will open and the _________ will come on.
door actuator; door; door light
in a landing gear system hydraulics operation, when the door is fully open, the ________ will redirect the hydraulic fluid to the ________ and the _________.
valve; gear up lock actuator; gear actuator
in a landing gear system hydraulics operation, this will lower the gear assisted by the weight of the gear.
gear actuator
in a landing gear system hydraulics operation, to control the speed of lowering, the returned fluid from the gear actuator passes through a __________ in the _________ flow direction.
one-way restrictive valve; restricted
in a landing gear system hydraulics operation, when the gear approaches the fully down position, a _________ in the lockdown actuator will push the geometric lock on the _________, locking the gear down.
powerful spring; center
in a landing gear system hydraulics operation, the _________ goes out and the _________ comes on.
red gear light; green light
in a landing gear system hydraulics operation, once the gear is locked down, the _________ directs fluid to the _________, _________ closes, and the _________ goes out.
door sequence valve; door actuator; door; door light
in other indicating system, newer aircraft with large LCD screens like in Airbus A320 Electronic Centralized Aircraft Monitor or ECAM will normally still have independent _________, but they also have the ability to provide further information about the landing gear system on a screen.
landing gear position indicators
in other indicating system, newer aircraft with large LCD screens like in Airbus A320 ________ will normally still have independent landing gear position indicators, but they also have the ability to provide further information about the landing gear system on a screen.
Electronic Centralized Aircraft Monitor or ECAM
in other indicating system, when the gear is locked down, there are ________ on both the _________ and on the _________ screen.
green down pointing triangles; undercarriage indicator; Electronic Centralized Aircraft Monitor or ECAM
in other indicating system, 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
in other indicating system, when the gear is up and locked, the displays are _________.
blank
in other indicating system, __________ are depicted by certain symbols.
door positions
in other indicating system, the symbols are _________ when the doors are _________ and _________ when they are not.
green; locked and closed; amber
