AIRCRAFT SYSTEMS LANDING GEAR Flashcards
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.
Functions of the landing gear
2 Landing Gear Layouts
Tricycle, Tailwheel
With slow, light aircraft, and some larger
aircraft on which simplicity is of prime
importance, a ___________ is often fitted.
fixed (non retractable) landing
gear
With higher performance aircraft, drag
becomes progressively more important, and a
___________ is retracted into the
wings or fuselage during flight.
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. The leg
consists of a tube, or strip of
tapered spring steel. The upper
end being attached by bolts to the
fuselage and the lower end
terminating in an axle on which
the wheel and brake are
assembled.
Spring steel legs
When ___________ is 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 an _____________ shock
absorber strut. The design of individual
struts varies considerably but the
operating principle is same for all.
Additionally, one point worthy of
consideration is the fitting of spats to
___________ strut.
oleo-pneumatic
These are an aerodynamic fairing
which may be required to minimize the
drag of the landing gear structure.
Spats
A _____________ consists of two
concentric cylinders, one free to slide inside the
other.
simple oleo-pneumatic strut
The cylinders are filled with hydraulic fluid and gas.
Fluid and gas are kept apart by a_________.
separator piston
The outer or upper cylinder is attached to the
___________. It houses the inner or lower
cylinder and a piston assembly.
airframe structure
The ___________ are connected to the bottom of
the inner cylinder.
wheels and axle
The inner cylinder is free to rotate and move up and
down within the outer cylinder. Rotary movement
and up and down movement is limited by the
__________ which connect the inner and outer
cylinders together.
torque links / torsion / scissor links
Landing gear is subject to_______
during ground maneuvering and these
loads are taken by the torque links.
torsion loads
The smaller the radius of turn, the
_______ will be the load felt by the
torque links so all turns should be
made as _____ as possible.
greater ; wide
The area on the outer cylinder is filled with
_____________ and the area on the inner
cylinder is filled with __________ which
may be air or nitrogen.
hydraulic fluid ; compressed gas
__________ is a free-floating piston which
keeps the fluid and gas apart.
Separator piston
The purpose of the hydraulic fluid is to ________________________________.
dampen oscillations and
control the rate of compression and extension of the cylinders
There is a component known as a _________
which is fitted to the lower cylinder piston
assembly. The _________ consists of a
free-floating circular plate with a large central hole.
It is free to move up and down within its housing.
flutter valve
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
cushioned by the gas
pressure and dampened by the limited flow of fluid
through the orifice.
Bumps during taxiing
gas pressure will cause the lower part of
the leg to extend to its fullest extent.
Takeoff
strut shortens, and fluid is forced through
the flutter valve.
Landing
Wheels to leg construction
Fork, Half Fork, Cantilever, Dual Wheel, Multiwheel
It is employed to improve aircraft performance by reducing drag
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
___________ are installed by which the
landing gear can be extended in the event of
failure of the power source.
Manual means
_______ are provided to prevent retraction
with the aircraft on the ground.
Systems
_________ are installed to guard against
landing with the landing gear retracted.
Warning devices
The leg is attached to the wing spars
by a ____________ on
which the leg is free to rotate
laterally.
cylindrical beam or trunnion
The strut inner cylinder is connected
to the ___________.
wheel bogie or truck beam
The ________ is able to pivot
about its central point in a controlled
way. There is an axle connected to a
pair of break wheels at each end of
it.
truck beam
The wing gear torque links prevent
________ between the shock strut inner
and outer cylinders without affecting
their reciprocating action during normal
operation of the strut.
rotation
The ________ supports the leg in fore
and aft direction.
drag strut
The ___________ struts
support the leg laterally. They fold out
when the gear is lowered and are then
held in place by the ________ strut which also
folds out during extension.
upper and lower side ; jury
The _______ is pulled over center by
the down lock actuator geometrically
locking the gear down.
jury strut
If the gear is lowered without hydraulic
power, then the over centering action
will be performed by an internal spring
in the __________.
downlock actuator
Loads Sustained by the Landing Gear
Compressive loads (landing and
static on ground).
Rearward bending loads (during
breaking)
Side loads (During cross wind
landings, take offs, and taxiing)
Forward loads (during push back)
Torsional loads (Ground
Maneuvering)
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
Design of nose landing gear are complicated by seven reqs, what are those?
Castoring
Self-centering
Steering
Anti-shimmy
Can withstand shear loads
It is 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
To enable the aircraft to be
maneuvered about the airfield, the
nose wheel must __________.
castor freely
_________ is 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 braking
____________ 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 ________________, a control valve steering cylinders to hold the nose gear, and a mechanical
feedback device to hold the nose wheel
at the selected angle.
cockpit steering wheel or
tiller
Steering is controlled depending on the
type of aircraft by either the tiller or
________________.
the operation of the rudder pedals
There are ____ steering actuators
which steer the nose gear.
two
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 __________ is
mechanically linked to the steering
control valve. A follow-up linkage
from the nose undercarriage gradually
resets the control valve as the nose
wheel turns.
steering wheel or tiller
There is a __________ fitted
between the two sides of the steering
actuators. It is normally held closed by
hydraulic pressure. The purpose of the
___________ is to allow the
nosewheel to castor if there is a
hydraulic failure.
safety bypass valve
Some systems have the facility to
bypass the system during towing
operations. It employs 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
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
