Landing Gear Components and Equipments with Possible Failures and Materials

1. Landing Gear Components & Equipment:
1.Struts
2.Steering Linkages
3.Tow Bars
Main Components:
1.Torque Links/Torque Arms/Torsion Links
(Scissors Assembly)
2.Drag Link/Drag Struts
3.Side Brace Link/Side Struts
4.Overcenter Link/Downlock Struts/Jury
Struts
5.Trunnion
6.Shock Struts
7.Shimmy Damper
8.Actuator/Jack/Actuating Cylinder
9.UpLock Cylinder/UpLock Actuator
10.DownLock Cylinder/DownLock Actuator
11.Indicator(microswitches/ground safety
switch/squat switch)
12.Centering Cam
13.Steering Actuator
14.Landing Gear Door Actuator
15.Emergency Lowering Mechanism

2. 1.Torque Links/Torque Arms/Torsion Links
(Scissors Assembly)
 It Maintain wheel and axle in a correct alinged position
in relation to the strut (misalignment corrected by
adding/installing a spacer or shim of different
thickness).
 Prevent ram of a piston turning in the struts.
 Restrict the extension of the piston during the extension
of the struts.
FUNCTION:
 The hinged link between the piston and cylinder of an
oleo-type landing gear shock absorber.
 The torque links allow the piston to move freely in and
out of the landing gear cylinder, but prevent it rotating.
 The torque links can be adjusted to achieve and
maintain the correct wheel alignment.

3. (Fig.1)
2.Drag Link/Drag Struts:
 Stabilizing the Landing gear and support the aircraft
structure longitudinally.
FUNCTION:
 A drag strut is used to restrain against the pivot action
built into the trunnion attachment
(Fig.2)
3.Side Brace Link/Side Struts:
 Stabilizing the Landing Gear and support the aircraft
laterally

4. (Fig.3)
4.Overcenter Link/Downlock Struts/Jury
Struts
 Holds the drag link and the side brace in the ‘DOWN’
and ‘LOCKED’ position by applying pressure to the
center pivot joint in a drag or side brace link.
 Operates hydraulically by bungee cylinder or
mechanically by bungee springs.
FUNCTION:
 The side brace assembly includes a jury strutvwhich
functions to lock the side brace assembly with the
landing gear in the extended position.
(Fig.4)

5. 5.Trunnion
 The trunnion is a fixed structural extension of the upper
strut cylinder with bearing surfaces that allow the entire
gear assembly to move.
 It is attached to aircraft structure in such a way that the
gear can pivot from the vertical position required for
landing and taxi to the stowed position used during
flight.
 Supported at its end by bearing/bushing
assemblies,which allow the gear to pivot during
retraction and extension (the struts form the cylinder for
the Oleo pneumatic shock absorber).
FUNCTION:
 The purpose of a trunnion is to structurally support the
landing gear in bearing the weight of the aircraft when it is
not flying.
(Fig.5)

6. 6.Shock Struts
 A typical pneumatic/hydraulic shock strut uses
compressed air or nitrogen combined with hydraulic
fluid to absorb and dissipate shock loads.
 It is sometimes referred to as an air/oil or oleo strut. A
shock strut is constructed of two telescoping cylinders
or tubes that are closed on the external ends.
 The upper cylinder is fixed to the aircraft and does not
move.
 The lower cylinder is called the piston and is free to
slide in and out of the upper cylinder.Two chambers are
formed.
 The lower chamber is always filled with hydraulic fluid
and the upper chamber is filled with compressed air or
nitrogen. An orifice located between the two cylinders
provides a passage for the fluid from the bottom
chamber to enter the top cylinder chamber when the
strut is compressed.
 Vertical member of the landing gear assembly that
contains the shock absorbing mechanism.
FUNCTION:
 Absorbs and dissipating landing shocks incorporates of
a telescopic tube mechanism which absorbs landing

7. shocks but resist re-bound and at the same time
protects the aircraft structure.
 Controlling the re-bound(spring back or
recoil)movement.
 Provi
ding
cushionin
g effects
during
taxiing.
(Fig.6)
7.Shimmy Damper
 A shimmy damper uses a cylinder filled with hydraulic
fluid or a rubber/lubricant combination to prevent rapid
movement of the nosewheel, while not interfering with
slower operations.
 Hydraulic snubbing unit that reduces the tendency of
the nose or tail wheel oscillate from side to side (rapid
oscillation).

8. FUNCTION:
 A shimmy damper uses a cylinder filled with hydraulic
fluid or a rubber/lubricant combination to prevent rapid
movement of the nosewheel, while not interfering with
slower operations.
 It turns the airplane, and the fluid squirts from one end
of the cylinder to the other. At higher speeds, the fluid
can’t get through as fast as the nosewheel wants to
shimmy, and the nosewheel is stabilized, preventing
shakin
g.
(Fig.7)
8.Actuator/Jack/Actuating Cylinder

9.  Landing Gear Retraction Actuators are designed to
provide retraction and extension forces while
maintaining light weight and reliability.
 Raise and lowering the landing gear.May also used as
a Downlock mechanism(continous application of
pressure).
 Retraction actuators are manufactured from complete
hog outs or finish machined from forgings to a one
piece body. Housings are commonly made out of
stainless steel for strength and anti-corrosive
properties.
 High strength and wear resistant materials are utilized
for the piston, end gland, and bearings to ensure
longevity and reliable service without the need for
overhauls or scheduled maintenance.
FUNCTION:
 The landing gear is rotated about a pivot by an
extend/retract actuator.
 To retract the landing gear, an unlock actuator pulls the
lock-stay from over-center, which enables the
extend/retract actuator to retract the landing gear to the
stowed position. Both the
extend/retract and unlock
actuators are typically
hydraulically powered.
(Fig.8)

10. 9.UpLock Cylinder/UpLock Actuator
 Locking the landing gear in ‘UP’ and ‘LOCK’ position
10.DownLock Cylinder/DownLock Actuator
 Locking the landing gear in ‘DOWN’ and ‘LOCK’
p
o
s
i
t
i
o
n
(Fi
g.
9)
11.Indicator(microswitches/ground safety
switch/squat switch)

11.  Means of providing cockpit indication with regards to
the landing gear position,either ‘UP’ and
‘LOCKED’,’DOWN’ and ‘Locked’ or in transition and
‘NOT LOCKED’.
 A landing gear squat switch, or safety switch, is found
on most aircraft.
 This is a switch positioned to open and close depending
on the extension or compression of the main landing
gear strut.
 The squat switch is wired into any number of system
operating circuits. One circuit prevents the gear from
being retracted while the aircraft is on the ground.
 There are different ways to achieve this lock-out. A
solenoid that extends a shaft to physically disable the
gear position selector is one such method found on
many aircraft.
FUNCTION:
(Squat Switch)
 The squat switch is essentially a sensor that senses if
the weight of the aircraft is resting on the gear.The
squat switch is wired into any number of system
operating circuits. One circuit prevents the gear from
being retracted while the aircraft is on the ground.
(Ground Safety Switch)

12.  A switch in the landing gear that prevents the
inadvertent retraction of landing gear on the ground.
This switch usually is located in the port landing gear.
(Fig.10)

13. 12.
Ce
nte
rin
g
Ca
m
 Aligning the nose wheel before retracted to ‘UP’ and
back to its wheel well compartment
 A cam in the nose-gear shock strut that causes the
piston to center when the strut fully extends. When the
aircraft takes off and the strut extends, the wheel is
straightened in its fore-and-aft position so it can be
retracted into the wheel well.
FUNCTION:
 The centering cam forces the nosewheel straight back
with the strut before it is retracted into the nose wheel
well.

14. (Fig.11
)
13.Steering Actuator
 Allowing the pilot to control or steer the aircraft by
means of NLG wheel assembly for taxiing.
 Nose Wheel Steering Actuators work in tandem to
provide linear push/pull forces for aircraft steering.
Actuators are sized for regional jets and large business
jets.
(Fig
.12)

15. 14.Landing Gear Door Actuator
 Allowing the opening or closing of landing gear door
(main and nose landing gear).
FUNCTION:
 When the doors are fully open, the door actuator
engages the plungers of both sequence valves to open
the valves.
(FIG.13)
15.Emergen
cy Lowering
Mechanism
 Providing
the means of
lowering down
the landing gear
in the event of
normal
extension
system fails

16. (under FAR 23.729).
FUNCTION:
 A device in an aircraft landing gear system that absorbs
the landing shock, which occurs when an aircraft
touches down when landing or during taxiing.
(Fig.14)
Materials Of Landing Gear
 The materials used for these components of landing
gear are composed of mainly High Strength
Steels,Titanium,Aluminium And Magnesium.

17. High Strength Steel
 High Strength Steel have strength and stiffness.
 High Strength to volume ratio is the main factor which
makes it important for the landing gear.
Titanium
 The titanium has high strength and low density used as
for weight saving.
 The main titanium alloy is Ti-5Al-5V-5Mo-3Cr,which is
used in the main components of landing gear.
Aluminium
 Modern aircraft consists of approximately 70% of
aluminium alloys.It has relatively low cost,light in weight
and can be heat treated to Stength level.
 Aluminium 7075 is used for the Landing Gear in
helicopters because it is strong,with a strength
comparable to many steels, and has good fatigue
strength.
Possible Failures Of Landing Gear
1.Fatigue Cracking Failure
2.Stress Corrosion Cracking

18. 3.Dynamic Failure
4.Landing Gear Spring Failure
5.Wheel Failure
1.Fatigue Cracking Failure:
Usually aircrafts and military experience serious damages
and the fatigues.
Equat
ions
used
for
analy
zing:
1.Paris
Equatio
n:
2.Forman Equation:
3.Walker Equation:
Effective Stress=(1-R)m
X Maximum Stress
2.Stress Corrosion Cracking:
SCC is defined as the crack propogation caused by a
synergy between a corrosive environment and a mechanical
tensile stress.

19. Stress Corrosion Crack Growth
3.Dynamic Failure
 When an aircraft lands on the tricycle landing gear(the
nose wheel and both landing gear) and the load
affected by the ground/pavement response are
distributed on them
 Numerical test showing stress analysis to define the
dynamic characteristics of the landing gear,with the
vertical-drop test
 Problem of contact between mating components and
surfaces of fractures
 Investigation into kinematics of the landing gear.
 Investigation into the problem of dissipation of energy in
the whole system.
 Checking of possible failure influence on the structure
behaviour.
4.Landing Gear Spring Failure

20.  T
he
Mic
ro
cra
cks
act
ed
as
str
ess
con
cen
trat
ion
as
wel
l
initiation crack site leading the springs to fracture due to
fatigue.
5.Wheel Failure
 During landing,wheels are exposed to a lot of pressure.

21.  Through this,overpressure may occur.This could have
the effect that the thread is thrown off.
Investigation photos show the damage was limited to tries and
rims only