Aircraft Landing Gear System Final
Aircraft Landing Gear System Final
Aircraft Landing Gear System Final
DEFINITION
This is the structure on the a/c or space craft consisting of the wheels, floats and related
mechanism that are used by a/c when taking off or landing.
MAIN FUNCTIONS:
1.Support the a/c on ground, water, or snow when stationary or when in motion.
The landing gear of the a/c consists of MAIN and AUXILIARY unit which may be FIXED or
RETRACTABLE
The main landing gear provides the main support and carries the most stresses during landing,
taxing, rolling, breaking etc. when the a/c is on ground.
3. FLOATS, PONTOONS
These are fitted on the sea plane and amphibians.
4. SKIDS
Skids are fitted mostly on the Helicopters.
5. SKIS.
These are fitted on a/c which operate off snow or ice surfaces
6. TAIL SKID
Fitted on a/c instead of tail wheel S
7. BRAKES
These are used to SLOW DOWN, STOPPING and PARKING the a/c.
The design loads which the aircraft landing gear must take:
1. SHOCK LOADS
These are the ultimate loads on touchdown, design for as much as 25 ft./scc
2. DRAG LOADS
These are caused by the following:
(a) violent spin-up of the wheels when the aircraft touches down
3. SIDE LOAD
These are caused by the following:
(a) turns on the ground especially at high speeds
4. WEGHT
This should have minimum weight strength /weight ratio.
5. RETRACTIBILITY
Except on light and slow aircraft, the landing gear must be retractable to reduce drag.(retractable
landing gear would be un economical)
Two main wheels are located ahead of the aircraft center of gravity and the tails is supported by
a smaller wheel.
steering on the ground is done by moving the tail wheel through the connection with rudder
pedals, usually through a spring
Tome tail wheelers have no provision for steering the tail wheel, but the wheel is locked in line
with fuselage for takeoff and landing and then unlocked, making it free to swivel, for taking,
control of the ground is then achieved by differential breaking.
c. cabin area is level, loading is easier and passengers find it easy to move inside the cabin
d. Makes aircraft stable on the ground operation and easy to control during take- off and landing.
3. Tandem landing gear
These are commonly used on some military bombers
The nose and Main are located in life under the fuselage and the wings are supported by
Outrigger wheel
1. Retractable or Non-retractable /
The landing impacts and taxing shocks over rough ground is eliminated by the shock-strut
This kind of design is provided in order to prevent these shocks to be extended to the main
structure and consequently to the passengers and the crew.
TYPES OF SHOCK ABSORBERS:
Generally speaking, some aircraft do not actually absorb shocks but rather accept their energy in
some form of elastic medium and return it at a rate and time that the aircraft can accept.
These types of spring steel struts accept shocks by flexing outwards and return the shocks in such
a way that it does not cause the aircraft to rebound.
Rebound is limited by the friction between the wheels and the ground with in a normal landing.
2. Rigid struts
These were used on older type of aircraft and all the loads where transmitted to the airframe
structure
The problem with this was that all the loads were transmitted to the structure and the occupants
and consequently could damage the structure
These can be in form of rubber dough nut or bungee cord which is a bundle of small stands of
rubber encased in a loosely woven cloth tube.
When the weight of the aircraft balances with the tension in the rubber, then the aircraft is in
equilibrium
The main parts are;
a. The leg or strut
b. Horizontal strut
c. Bungee (Rubber) chords
d. Rubber blocks
4. Oleo - pneumatic shock-strut
This is also referred to as Air-Oil strut
This type of shock-strut uses hydraulic oil and natural air e.g. nitrogen
c. Torque links
d. Piston
e. Charging valve
g. Fork.
The lower cylinder is free to move up and down into the cylinder (telescope) and moves with the
whc
Torque links
Scissors
Nut crackers
3. Prevents the lower strut from coming out of the upper strut
The upper link of the torque link is attached to the cylinder (upper strut) and the lower link is
attache the lower strut (the upper strut is the cylinder and the lower strut has the piston).
The cylinder is divided into two compartments by piston tube and piston itself fits into the
cylinder. A tapered metering pin which is part of the piston sticks through the piston tube -
When the wheels contact the ground on landing, the piston is forced up into the cylinder and
much of ti energy of impact is absorbed by forcing the fluid through the restricted orifice.
The tapered or taper of the pin provides a graduald amount of opposition to the flow and
smoothly absorbs the landing shocks.
When the weight of the aircraft is removed from the landing gear like at take -off the piston
extends th full amount allowed by the torsionltorque links and fluid drains past the metering p[in
into the fluid chamber in the lower strut, hence controlling rebound.
Note:
4\
1. Landing impact / shock is absorbed by telescoping mechanism where the oil is itcing when
flowing to the upper chamber through the orifice.
2. Rebound is controlled by the oil flowing back to the oil chamber when the lower strut ten to
extend out-wards
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This is the most widely used shock absorber.
1. Retractable or Non-retractable
When the aircraft touches down, it is the tyres to touch first and then the shock is absorbed.
The landing impacts and taxing shocks over rough ground is eliminated by the shock-strut
This kind of design is provided in order to prevent these shocks to be extended to the main
structure and
Generally speaking, some aircraft do not actually absorb shocks but rather accept their energy in
some form of elastic medium and return it at a rate and time that the aircraft can accept.
These types of spring steel struts accept shocks by flexing outwards and return the shocks in such
a wa
Rebound is limited by the friction between the wheels and the ground with in a normal landing.
2. Rigid struts
These were used on older type of aircraft and all the loads where transmitted to the airframe
structure
The problem with this was that all the loads were transmitted to the structure and the occupants
and
These can be in form of rubber dough nut or bungee cord which is a bundle of small stands of
rubber
When the weight of the aircraft balances with the tension in the rubber, then the aircraft is in
equilibriurr
b. Horizontal strut
c. Bungee (Rubber) chords
d. Rubber blocks
This type of shock-strut uses hydraulic oil and natural air e.g. nitrogen
c. Torque links L
d. Piston
e. Charging valve
g. Fork.
The lower cylinder is free to move up and down into the cylinder (telescope) and moves with the
wh
Torque links
Nut crackers
3. Prevents the lower strut from coming out of the upper strut
The upper link of the torque link is attached to the cylinder (upper strut) and the lower link is
attache the lower strut (the upper strut is the cylinder and the lower strut has the piston).
The cylinder is divided into two compartments by piston tube and piston itself fits into the
cylinder. A tapered metering pin which is part of the piston sticks through the piston tube
When the wheels contact the ground on landing, the piston is forced up into the cylinder and
much of t energy of impact is absorbed by forcing the fluid through the restricted orifice.
The tapered or taper of the pin provides a gradua(e{ amount of opposition to the flow and
smoothly absorbs the landing shocks.
When the weight of the aircraft is removed from the landing gear like at take -off, the piston
extends tl full amount allowed by the torsionltorque links and fluid drains past the metering p[in
into the fluid chamber in the lower strut, hence controlling rebound.
Note: V
%4-\ -\
1. Landing impact I shock is absorbed by telescoping mechanism where the oil is ntcrin when
flowing to the upper chamber through the orifice.
2. Rebound is controlled by the oil flowing back to the oil chamber when the lower strut ten to
extend outwards
Other types of struts which use separators and flutter valves or small orifice within the piston are
in design.
In the former design oil chamber and air chamber have separate charging salves.
It uses a synthetic silicon-based compound with molecule so large that they distort considcabiy
under
pressure.
Landing shocks:
They are absorbed by the liquid being compressed on touch down and also the liquid flowing
through th valves and piston orifice.
Rebound:
Rebound is controlled by the valve closing and liquid flowing through the restricted orifice.
1. It is very compact
Main undercarriage.
The main landing gear is attached near the center of gravity to undertake most of the load.
Auxiliary, undercarriage.
1. Nose-wheel
2. Tail wheel
3. Tail skid
4. Pontoons
5. Outriggers
The distance between the main under carriage is called TRACK and wider the track, the more
stable tJ aircraft will.
The distance between theose wheel and main wheel centers i called th WHEEL BASE.
TOE-IN
0
This is the deviation of the tire from ahead a straight ahead condition (in ward alignment of the
wheel)
It allows for rearward flexing of the struts due to the drag loads
If an aircraft was not incorporated with some toe-in, during taxing the aircraft would experience
toe o and struts would stretched beyond limits.
TOE.. OUT
This is the deviation of the wheel from straight ahead condition but (out ward outward ahignme
the wheel).
CAMBER
It allows the flexing of the spring strut and rubber in tension struts due to aircraft weight
When the wheel inclines outwards, then it has positive camber and when inclined inward, it has
negative camber.
The wheels must follow paths parallel to the longitudinal axis of the aircraft
This check should be carried out at empty weight (cabin and fuel tanks empty), so as to obtain
zero in and camber at maximum takeoff weight authorized (M.T.O.W.A).
i ccjr I.
ii.
fr 1
Roll the aircraft and place each wheel on a pair of greased plates (grease between the alumini
plates).
Rock the wings of the aircraft, this will allow wheels and the aircraft to assume their true natu
positions of alignment.
Mount a straight edge on the suitable blocks across the front of the wheels just below the axle
Place large carpenters square against the straight edge so that it touches the wheel just belo the
axle nut.
v. Measure and note the distances between the square and the wheel flange at the front and the re
vi. The difference betiveen the two readings (between the square and the wheel flange at the fror
and rear should) p..
vii. The difference between the two readings should not exced V2 (halO the total Toe-in(check
with manufactures quotations)
viii. Toe-in or toe-out on a spring steel strut can be adjusted by using tapefred shims Letween the
- landing gear leg and the wheel axle.
ix. On other landing gear, Toe-in or Toe out can be adjusted by repositioning the washers
between the torque links of landing gear of oleo-strut.
Camber can be adjusted by use of shims between the axle and the landing gear leg to give zero-
degree camber at the weight at which the aircraft is most generally operated.
iii. Compare the readings with the limits specified in the maintenance manual.
Non retractable landing gear is normally attached to the structure by bolting the landing gear to
structure
directly
Retractable landing gear system must provide for landing gear to move, so the upper shock-strut
is attached to the structure using Trunion fittings.
Owing to drag and side loads, which tend to bend the undercarriage struts it is necessary to
reinforce sufficiently to be able to withstand these loads.
These are attached to the landing gear and are in line with the longitudinal axis of aircraft- take
up drag loads
2. Side struts
These are perpendicular to the aircraft longitudinal axis as viewed from the rear and front(take
side loads)
3. Trunnions
These type of landing gears are always fixed in the extended position whether the aircraft is
flying or ground.
Disadvantages:
Parasite drag is that drag caused by those parts of the aircraft which do not contribute to lift.
In order to reduce this kind of drag on light aircraft, the following can be done;
b. Enclose the struts in stream lined fairings to reduce frontal area presented to the airflow.
This is the type of landing gear which can be retracted and extended
b. They also eliminate structural damage of the 1arding gear which can be caused by the high sp
airflow resulting in under carriage blown off.
a. Inthe wing
b. In the fuselage
a. Forward
b. Rearward
c. Sideways
Doors are further provided to cover the wheels to reduce further on the drag and to prevent
damage f foreign object like dust, gravel, stones etc which would find their way into the wheel
well.
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1. Manual system
When the electrical system fails a manual system (emergency) can be operated by the pilot.
a. Levers
b. Handles
d. Chains
2. Electrical systems
The power to move the landing gear is provided by electricar motor which can operate the
mechanism through gear box or transmission assembly.
The system is actually electrical mechanical because electrical power drives the mechanical part
of The operation is through actuators and mechanical linkages
The system incorporates limit switches /micro switches /squat switches which automatically cut
off power to the motor when the gear is at the extreme end of its travel.
Other micro switches are provided to operate the position indicating and warning system and
also the ground flight mode.
3. Hydraulic system
Hydraulic power is used to drive actuators or jacks which in turn drive mechanical linkages to
extend o retract the landing eyo(
The main advantah of hydraulic system is that it is capable of transmitting forces and
undiminishing Oi large distance.
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The power is obtained from the main aircraft hydraulic system and consists of the following;
a. Control lever C
c. Hydraulic pressure control valves (flow control and pressure control valves)
Operation of the system it its proper operation is governed by a number of valve e.g sequence
valves selector valves, non -return and other control valves.
4. Pneumatic system
The basic principle of operation of pneumatic system is similar to the hydraulic system, the
difference being that compressed air is used to transmit the force instead of hydraulic fluid.
We have already seen that landing gear can be retracted or extended by different means of power
The landing gear selector handle is placed in the gear up positions in the cockpit on the landing
gear control panel.
For electrically operated pump system, a pump will be started by the action of this switch and
fluid w forced into the actuating cylinder and the landing gear will raise.
But the initial movement of the piston in the actuating cylinder will raise the landing gear down
lock that the landing gear can be released and retract.
When all the three wheels are completely retracted up and locked a pressure switch will stop the
pum In some systems, there are no up-locks but the gear is held in its retracted position.by
hydraulic press built in the actuator. But if the pressure drops enough to allow any one of the
wheels to drop away
its up-limit switch, the pump will start and restore pressures
This action will release pressure on the upside of the operating cylinder (actuator)
The landing gear will have a free fall and then pump will start working to build pressure and
ensures gears aren and locked.
ien they all down and locked, the limit switches will shut off the pump.
All retractable landing gears must have a means of lowering the landing gear in the event the
main
extension system fails.
They are many methods used to lower the landing gear in emergency situations;
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i. Mechanical method
In all cases the emergency extension systems purpose is to release the Up-lock and move
landing ger to down and locked position.
The mechanical method is operated manually by the pilot or crew member through mechanical
linkages which will include the following.
- Hand-crank or level
- Rocker chain
- Sprockets
This manually operated system is commonly employed on small and some medium aircraft e.g
Cessna 310.
When an emergency lever is selected, store pressure in the accumulator is released to extend
landing - The compressed air emergency system allows the landing gear to be extended in case
the hydraulic syst fails.
The shuttle valve is the system allows the compressed air to enter the actuator (same operating
cylinder from one end and extends landing gear.
The normal hydraulic line will be blocked off by the sliding shuttle valve.
The free-fall (automatic) extension system will allow landing gear to lower regardless of the
landing ge selector handle in the cock pit.
When the aircraft is in the landing configuration and the landing gear is not extended, the system
will automatically release the locks and extend the landing gear.
Landing configuration:
NOTE: A manual over-ride is provided to prevent the operation of auto-system during low
speeds take off, and certain training exercise.
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These are safety devices or systems when the aircraft is ground or in fligl}t.
a. Safety switches
This provides a means of preventing the retraction of landing gear while the aircraft is on ground
If the aircraft hydraulic system is powered and the landing gear handle is inadequately moved to
the position, the landing gear would retract, and this would cause a lot of damage to the aircraft
To prevent this from happening, a switch connected to the aircraft landing gear is installed where
by t retraction system is completed through the same switch.
When the aircraft is off its weight, the circuit can be completed and retraction is possible
(remember aircraft is off its weight, the lower shock-strut extends outwards).
b. Locking devices:
i. Mechanical Locks; these are form of locks which form a physical barrier to the move of
landing gear parts.
ii. Hydraulic locks; this kind of locks maintain hydraulic pressure on one side of the pisi the
actuator or operating cylinder
iii. Geometrical locks; these are used to lock the landing gear when the aircraft is on grol these
locks are engaged when the aircraft lands to prevent inadvertent retractier They are fitted by
technician and fitted in part of the struts.
NOTE: These mechanical pins which are fitted in special positions on the strut and always carry
ap flag-and should be removed when the next flight is ready.
i. Mechanically operated
c. position indicators
Landing gear position indicators are also located in cock-pit on the landing gear control panel
The landing gear position indicators will be in form of;
i. Lights
iii. Needles
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Some modern aircraft (large) have landing gear doors open light and also some landi gear
disagreement light.
Other airraft have landing gear DOWN AND LOCKED light on the outside pn eaci landing
gear which can be visible by the persons on ground or Control Tower - ATC.
d. warning system:
The warning system is used to inform or alert pilot if the landing gear is not down and locked
during a
This warning is always audible; some of them can be accompanied by flashing red light.
i. Horn
ii. Bell
There are so many variations from system to system, but they all base on the basic idea of
warning the
pilot that the landing gear is not down and locked position while in the landing configuration.
Most aircraft with retractable landing gear are fitted with gear landing doors which seal off the
wheel w and maintain fuselage or main plane contour
1. Eliminate drag that would result from turbulence around the wheel area (streamline)
2. Protect the wheel well and wheels from foreign flying objects (fluid lines and other
components)
3. Avoid high air pressure energy which could lead the doors to flying off.
The doors are normally constructed of rein enforced skin panels and are operated by the
following mea Mechanically by linkages to the landinggear mechanism to hydraulically or
pneumatically by a separat actuator which are controlled by sequence valve to ensure that
novement of the landing gear does not occur before the doors are out of the way.
The operation cycle of the landing gear doors door is; CLOSE OPEN CLOSE.
The lights are operated by micro switches which are in turn operated by contact with part of the
retract svsterr -
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The individual lights in the cock pit ar normally provided with PRESS TO TST (P.T.T) switches
- which are serviceability test switches
Miniature gears (wheels) or needles tjpe of indication system may be opated electrically or by,
mechanical linkages to the retraction.
The nose wheel is equipped with centering mechanism e.g. centering cam located in the nose
wheel shock-strut.
These cants centers the nose wheel when the strut is extended after take off
The nose wheel will remain center until the weight of aircraft, upon landing contacts the struts
movin cans away from their slots.
When the cans are moved away from their slots, the wheel can now turn as commanded by the
steerii system through rudder pedals
The centering tnechanisuz also allows the landing gear (nose,) to retract into their wheel well as
required without binding on the structure.
During retraction, the itose wheel is prevented from rotating because of the following dangers;
- Fire hazard
If the wheels are retracted into their wheels wells when rotating, there is a possibility of structure
cat fire if the wheel came into contact with any structure in the well.
If the wheel is rotating during retraction it might oppose the desired direction to be turned to.
Remedy:
i. The pilot has to apply brakes after take- off especially on the medium and large aircraft.
ii. On some aircraft, the braking system is designed in such a way that if the aircraft takes off ai
gear is being retracted, hydraulic fluidis directed to the brake system to stop the wheel from
rotating. (Remember some aircraft have nose wheel brakes).
iii. On some aircraft nose wheel, an asbestos pad is incorporated in the wheel well to cause frict
and stop the rotating of the wheel since asbestos is a bad conductor of heat.
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1. Gear latches
The landing gear latches or up and down locks must be adjusted so that the gar will lock in the
full up- and down position without binding.
The gear must remain locked after the gear handle is moved to the off or neutral position
The gear can be adjusted by setting the retraction rod end at the doors so that door will pull up
tightly
Check all the rods ends for adequate thread engagement for safety and tightness ofjam (lock) nut.
3. Landing gear retraction check
Determine that the main gear is properly adjusted for full travel from gear up to gear down.
This is accomplished by cycling the gear up and down while watching for looseness, binding and
chaffing of the gear and related parts
The gear should be checked so that thcy pull up tightly when the gear is fully up
Check all gear components for damage, safety, tightness and any general condition rectify
where possible.
4. Emergency extension
The gear up warning horn, light or any warning sound or signal should be cijecked during the
retraction test follow maintenance.
5. Maintenance of shock-cords.
But regular inspection must be carried out according to the maintenance schedule.
According to MIL-C-5651A, the colour codes for the year is repeated in cycles of five years Two
spiral threads are used for the year coding and one thread for the quarter of the year.
Example if inspecting shock cords in 1986 and found that the chord had two yellow threads and
one blue thread spiraling around the sheath, the technicians should know that the cord was
manufactured in 1964
1964-1969 YELLOW
1965-1970 BLACK
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The air-oil (oleo) strut should be maintained at proper strut tube xposure (extension) for proper
pper of the shock- strut
Both the nose and main gear strut will have a specific length of piston tube exposed
The measurements of these valves should be taken when the aircraft is on level ground with
normal fu loading conditions.
The first step to be taken is to clean the top of the strut to remove the dirt, dust and other partic
from around the filler plug.
Place a drip pan under the landing gear to catch spilled oil
Relieve the air pressure from the strut (repress the valve or use key)
When air is out completely, remove the filler plug from the strut
Push in the strut piston tube (lower strut) until it is fully compressed by pushing up the tyre.
Get a clean container and pour oil through the filler plug hole until it reaches the bottom of the
filler plug hole.
Install the plug finger-tight, and extend and compress the strut two to three times to remove air
from the housing
Remove the filler plug, then raise the strut to full compression and fill with fluid if needed.
After ascertaining that if full with oil, then the next step is to inflate it
Inflate the strut with nitrogen until the correctin extension is obtained(exposed)
Rock the aircraft several times to determine if the gear returns to correct strut position
Before replacing valve cap, check the leakages using soap solution
Please always refer to the aircraft maintenance manual for correct valves and limitations
When checking for landing gear position and warning system, the following are checked
18 I
Position indicator lights are checked by cycling the landing gear while on jacks a number of
times and checking that lights correspond to the state of gear. e.g when the green1light comes on
the landing gear must be down and locked and the brace struts must be in their over -center
position.
The warning ystem must also function tested periodically according tp the maintenance
schedule or when malfunction reported
This test is done by placing the throttle and flaps in a prescribed minimum position and
checking that the warning comes on.
On some aircraft the time taken for the gear to extent or retract is specified.
When the doors are closed, they should seals the wheels well properly without buckling
Shimmy is the rapid side to side movement of the nose wheels as te moves at speeds on the
ground.
The geometry of the nose landing gear makes it possible to shimmy or oscillate back and forth r
certain speeds, sometime violent.
To prevent this kind of undesirable condition, all nose wheel oleo-strut are equipped with
shimmy damper. (Prevents side by side oscillation of the nose wheel).
3. VANE-TYPE DAMPER
Heavy aircraft normally use the steer dampers which are dual purpose.
Large aircraft are steered on ground by directing hydraulic pressure into the cylinder ofa dual
shimmy damper.
Fluid from opposite side of piston in these cylinders is directed back to the system fluid reservoir
through a pressure relief valve that holds a constant pressure on the cylinders to snub any
shimmy.
An accumulator in the line to the relief valve holds pressure on the system when the steering
control valve is in its neutral position.
A small control wheel I steerinj tiller sometimes used by the pilot directs hydraulic fluid under
pressure into one or the other side of the steering cylinders.
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Relatively small and medium aircraft can use both piston type and vane type shimmy dampers.
This is basically a piston moving into a fluid- filled cylinder. - The piston is provided with small
orifices through which a controlled fluid flow is forced from one si the piston to the other
The restricted or controlled flow of fluid prevents movement of the piston being too rapid, but
has no effect on normal steering.
AIRCRAFT WHEELS
b. Tyres
c. Brake discs
The wheel assembly is attached to the wheel axle-to support the aircraft on the ground
The wheel is the highly stressed part and its failure can lead to serious damage to the aircraft and
injur personal
The bead seat area is the mostly highly strengthened part so that it can bear high loads applied by
the t
2. SPLIT- TYPE
Was used on early aircraft and tyres where installed the same way the tyres are forced on the
auto mole or bicycle wheels.
The spilt-type
This is made Into two halves joined together by high tensile steel bolts and selflocking nuts.
If tubeless tyres are installed into them they must be installed with a seal between them
wheels fitted with tubeless tyres will also have an inflation valve permanently installed in them
(one of the half)
Wheels for tubed tyres wilLsimply have a hole drilled in one of the valves to permit the
inflation valve on the tube to protrude.
Two bearings, one in each wheel half fit over the axle and permit the wheel to rotate with
minimum friction.
the bearing assembly consists of the bearing cone, roller bearing, retaining cage, bearing ca
outer race
A grease seal cover is installed to hold the grease in bearing and to prevent any dirt or wat
getting into its surface
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This in board wheel half will take up the brake disc and the brakes
CC
This bolts to the inboard half and also holds a shrunk in the bearing cup in which bearing cones
rides It also takes up a seal to protect the roller bearing and their surfaces from water and dirt or
dust, as well a:
A cap is held in place with retaining ring to cover the end of the axle shaft and bearing.
If the aircraft is fitted with Anti- skid system, this cap is fitted with a bracket to drive the wheel
speed sensor (transducer) which is installed in the axle.
An installation valve is installed in this out board wheel half in case tubeless tyres installation,
and in cas of a tube tyre installation, a hole will be drilled to allow inflation valve to stick out.
When a brake drum of conventional type is installed on each side, of the wheel, this provides a
dual b .
assembly.
FUSIBLE PLUGS
Two or more fusible plugs are installed in the board half of the wheel ofjet a(Cfor the purpose
of releasing the air from the tyres in the event of an extreme over heat condition; such might
exist
Rather than allowing the heat to build up the tyres pressure so high that the tyre blows out, the
low-melting point alloy in the center of the plug will melt and harmless(material in center of plug
has low melting point)
The escape of air from the tyre will be gradual rather than spontaneous
WKEEL INSPECTION
(a) In-Situ
ii. Check for proper installation of the brakes and brake discs
iii. Check for mounting or mating of drive tags between the drive slots rather than mating with
slots
iv. Check for axle nut torque, check for proper torque value from the aircraft maintenance
manual
I. The first thing to do when the wheel assembly is removed from the aircraft is to completely
deflal the tyre-aiways use deflector cap screw
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ii, Loosening the tyre from the rim using the proper method and tools like bead breakers never us
sharp tools like screw drivers.
iii. Disassemble the tyre by removing the bearing seals and cones fron the valves.
iv. Clean the wheel assembly uing recommended solvents like Stoddard solvent or any othr
approved, for that purpose. use a soft brush to remove stubborn deposits, dont use any scrapper
v. After cleaning, clean the bearing and dry them with compressed air (keep pressure relatively
lo dont rotate dry bearing.
vi. Bearing inspection should be carried out after removing the bearing from their recesses or
fron axle using a puller.
Grease can be worked into the rollers manually or using pressure packing
Spread alight film of grease on the bearing cups and bearing surfaces
viii. Wheel valves should be inspected. Especially the bead seat area.
The wheel valves can be checked for cracks in bead seat area using non -destructive testing
method e.
- Dye-penetrant
- Fluorescent dye
- Magnetic particle
- Eddy current
- X-ray
- Ultra sonIc
The most recommended method are eddy current and clye-penetrant methods
ix. Wheel bolts are checked for cracks using magnetic particle method.
The most affected areas are around the junction of shank and the head and to the end of threaded:
x. Fusible plugs should be checked to ascertain that there are signs of melting.
If one of the plug shows this sign or any deformation, replace all the fusible plugs.
xi. key and key screw should be inspected for play or looseness, cracks or excess wear (keys to tr
rotate V the discs against the friction in the brakes).
xii. Wheel balancing should be carried out to eliminate vibration during rotation.
All wheels having a diameter of more than TEN inches should be statistically balanced when
Provision is made on the wheel for attachment of these weights (add weights to lighter side).
If the weight were removed for any reason, they should be fitted back in their original positio
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The shaft is then placed on the balancing stand and the wheel assembly is allowed to rotate
until it heavy point comes to rest at the bottom.
Counter balance the wheel assembly with test weights until it is balaflced.
b. By using cotter pins through holes that were drilled in the rim for that purpose
c. By using lead strips having an adhesive backing are used especially for smaller wheels
(consult th service manual for the correct type of weights).
AIRCRAFT TYRES.
Aircraft tyres are required to absorb a great load imposed on them a.j!.touch braking and
stopping the aircraft, high rotational speeds associated with takeoff arc landing, and also to
provide cushioned ride while resisting heat generation.
Therefore they are manufactured to meet high rigorous demands of their jobs (to accept a variety
of static and dynamic stresses)
Example is that jet transport aircraft tyres which can withstand speeds at landing (landing
speeds) of about 250 mph and well as dynamic and static loads as high as 22-33 tons
respectively. Aircraft tyres are designed to allow maximum deflection of around 32-35 which is
more than twice the motor vehicle tyres,
Tyres for aircraft are made of rubber reinforced it1i steel wire braid and nylon fabric plies.
TYRE CLASSIFICATIONS
a. TYPE
b. SIZE
c. PLYRATING
d. TUBE OR TUBELESS
I,
23
Tyre sizes.
Dimensional tolerances are set by the Tire and Rim Association (T&RA) and/or the European
Tyre an
bias tire dimensions are for a New tire that has been inflated to the specified pressure for 12
hours minimum.
Radial tire dimensions are for a Grown tire that has been rolled the equivalent of 50 TSO-C
take-off cycles.
TYPES
Nine types of aircraft tyres have been established by united tyre and rim association, but only
three ot these types are of primary concern to day.
Type iii
This is the most popular low pressure tyre found today on piston-powered aircraft characteristics.
A tyre having a section width of nine inches and which fits on a sixteen inch wheel would be
identifi as tyre (9.00-16) tyre. (W D. Nominal section width - Rim diameter)
Type vii
Characteristics:
26 x 6.6
x1Z
L k%._r
24
Used for all recent and newly designed tire sizes, all applications.
27 x 7.75 15
Size designation: Do x W R D.
50 x 20.0 R 22
TUBES are sized and identified the same way as the tire size for which they are to be used.
Examples:
6.006
15x6.06
Type viii
This type of tyre is for high performance jet aircraft with extreme take- off and landing speeds
Characteristics
- Low profile
- Designation of size is by outside diameter and section width and rim diameter
For example a tyre designated for a Type viii tyre would be;
3011.50-.14..5
SECTIONAL WIDTH
PLY RATING
Ply rating is the number given to the tyre to express its strength characteristics.
It does not specify the actual number of fabric ply in the carcass but relates the tyre maximum
static ba
E.g. 8 PR 3 Ply rating (refers to maximum static load and inflation pressure).
25
TUBE OR TUBE LESS
The basic 1ifierence between the types is the iner liner for tubeless tyres whih S that serves as
container for air.
Tubeless tyres will have a mark (TUBELESS) on the sides but tube tyres will have NO MARK.
Tube type tyres will have smooth inside so the tube will not be damaged by chafing against the
inside of the tire
All information pertaining to classification and identification of the tyre will be enclosed on the
side wall:
As already mentioned that aircraft tyres are made from rubberized reinforced with steel wire
braids and nylon fabric plies
Dissecting an airbrafi tyre will show that it is one of the strongest and toughest pneumatic tires
made.
I. Bead
Bead wires anchor the tire to the wheel and transfer the load to the wheel.
It anchors the carcass and provides affirm mounting for the tyre on the wheel
Ultimacly all the ground forces on the tyre terminates in the bead
Rubber pcx strips stream line the round bead bundles, so the fabric will fit smoothly aroun
them.
2. Flippers
These are layers of rubber and fabric enclosed the bead bundles to insulate the carcass plies fro
Since the greatest amount of heat in the tyre is in bead area, this kind of insulation increases&
durability of the tyre. V
The term easing ply and carcass ply are sometimes used interchangeably.
A casing ply consists of fabric cords between two layers of rubber representing an individw
ply.
Casing p[ies are anchored around bead wires forming ply turn-ups.
MultipV i:!yers of casing plies are bonded together, as necessary, to form the casing and gi4
Meanir. that the cords of fabric run at angle of 45 to the length of the strip
Each sueccssive ply of fabric is put on in such a way that the chords cross each other at abc
26
The tread refers to the part of the tire that comes in contact with the ground, i.e. the wearing
surface on the outer circumfe-ence of the tyre.
The tread rubber compound is formulated to resist wear, abrasion, cutting, cracking, and heat
buildup.
It is made of specially compounded rubber and has a pattern of grooves molded into its surface t.
give the tyre the required tractions characteristics with the type of run way surface the aircraft w
encounter.
It prolongs the life of the casing by protecting the underlying tire structure.
5. Tread Groove:
These are circumferential grooves molded into the tread surface during fabrication.
a. Act as a visual indicator of tread wear by allowing easy depth perception of the skid depth to
the bottom of the groove.
b. Provide a mechanism to channel water from between the tire and runway surface.
6. Tread Ribs
Un deli read:
Undertread is the rubber layer between the bottom of the grooves and the top of the reinforcing
Plies on Bias tires nd the top of the protector ply on Radial tires.
For tires designed to be retreaded, it allows for buffing the worn tread and provides the liaison
with the new retread products.
a) Plain treads
It is plain; smooth no brakes or vhose brakes are used as a taxi aid other than slowing down
aircraft on landing.
Currently they are found on very light aircraft and some helicopters.
Water dispensing treads have small holes in the crown and shoulder rubber to prevent aqua
planning.
This is a diamond shaped treads pattern for aircraft operating on grass or hard packed dirt
The same tread type can also be very good for braking action on both hard surfaced and dirt
runways if t tyre has a rib tread in the center and diamonds molds into the shoulders.
27
Designed especially for use on hard surface runways and gives long tread wear, hood retraction
and exceptional good directional stability.
These are single or multiple layers of a special nylon fabric positioned underneath the tread.
These plies help to strengthen and stabilize the crown area by reducing tread distortion under
8. Breakers
But they are extra-layers of reinforced e.g nylon cord fabric placed under the tread area
9. Bead toe:
This is the inner bead edge closest to the tyre center line.
This is the outer bead edge which fits against the wheel flange
For tube type tyres. a thin rubber liner is used to prevent tube chaffing against the inside ply.
12. Sidewall
This is a rubber covering that extends from the tread down to the bead heel to protect the carcaSS
from such injuries as cuts, bruises and exposure to ozone and moisture.
Protective rubber laid over the outer casing plies in the bead area of the tire.
Its purpose is to protect the casing plies from damage when mounting or dismounting and to
reduce the effects of wear and chafing (light abrasion) between the wheel and the tire bead.
This technology uses a newly developed ultra-high tensile composite cord with less elongation
than nylor cords.
28
Tires constructed with NZG cord may use fewer plies to achieve the same tire strength and
capability
As such, NZG tires are lighter in weight and grow less than nylon constructed t i res.
Jet aircraft with rear -mounted engines have a problem with water or slush being thrown up b,
nose wheel and entering into the engines, causing damage or flame out.
This is prevented by using nose wheels with chines or deflector molded in the upper side wall
the tyre to deflect the slush or water away from the engine intakes.
NOTE
A tire can have a single chine for dual nose wheel tire configurations or double chine for single
wheel tireconfigurations.
The chine tire is used on some commercial, regional and private jets. It is re-treadable when
specified.
TYRE VENTING
Tubeless tyres have an inner liner to prevent air escape but in actual sense sometimes air escapes
If this seeped. air is entrapped in the body plies, it could expand when the tyre heats up and cause
ply
To prevent this tubeless tyres have vent holes in both their lower sidewalls to allow this air to e
Some air is also. available in the casing cords after manufacture, hence needed to be eliminated.
These holes can also release the air which is entrapped between the tyre and the tube when the
tyre a
Paint dots are applied to new tires. It is not required that they be refreshed on
retreaded tires.
Notel:
Not all tires require vent holes due to materials, design and fabrication.
This is particularly true for some physicaLly smalLer radial tires used in the General Aviation i
Note 2:
It is normal to see bubbles at the tire vent holes, just above the wheel flange, any time while tli is
inflated.
N0Th3:
Do not identify a tire as leaking solely on the rate of bubbles from the vent holes.
- -c L
- r . .
29
TiRE TERfVlNOLOGY
A New Tire
hhis is a tire that has been stretched t its dimensions by inflatingto hepecified pressure and that
has been placed in service on an aircraft.
Grown tire
Tyre that has been stretched to its maximum dimensions during its service life, as a result of
inflation pressure, heat, and rotational forces.
B or II prefix in the size designation indicates a rim width to section width ratio.
This is maximum diameter of a new inflated tire measured on the center bf the tread.
Section Width.
This is the overall width at the widest point of a new inflated tire.
The section width dimension does not include the chine for tires with chine.
The Construction code is placed between the section width and the rim diameter.
This is the distance between the center of the wheel axle and the flat surface, on which the tire is
bade
when supporting its rated load while inflated to its rated pressure (at ambient temperature). V
Tire Deflection. V
This is the difference between half the outside diameter and the static loaded radius. V
TYRI! INSPECTION:
1. INFLA TION
The greatest enemy of the aircraft tyre is heat, either that jSV generated within the time as It rll
the ground or that from such external source as the brakes or hot runways. V As the tyre rolls its
side wall flexes and cause internal heat V
The tyre is inflated to have a normal flexing for a reasonable amount of time and at the same t
aircraft weight is supported by the air in the tyre. V
Therefore the inflation pressure is critical and should be checked daily and before each fligh Use
a serviceable pressure gauge (manometer) when checking tyre pressure.
excess flexing., V V V V
29
TE TERMlt1OLOGY
A New Tire
his is a tire that has been stretched t its dimensions by inflatingto hpecified pressure and tharha
been placed in service on an aircraft.
Grown tire
Tyre that has been stretched to its maximum dimensions during its service life, as a result of
inflation pressure, heat, and rotational forces.
B or ii prefix in the size designation indicates a rim width to section width ratio.
This is maximum dianieter of a new inflated tire measured on the center bf the tread.
Section Width.
This is the overall width at the widest point of a new inflated tire.
The section width dimension does not include the chine for tires with chine.
The Construction code is placed between the section width and the rim diameter.
This is the distance between the center of the wheel axle and the flat surface, on which the tire is
bade
when supporting its rated load while inflated to its rated pressure (at ambient temperature). V
Tire Deflection.
This is the difference between half the outside diameter and the static loaded radius. V
TYR INSPECTION:
1. INFLA TION
The greatest enemy of the aircraft lyre is heat, either that is: generated within the time as Vt roil
the ground or that from such external source as the brakes or hot runways. V V V As the tyre
rolls its side wall flexes and cause internal heat V V V The tyre is inflated to have a normal
flexing for a reasonable amount of time and at the same t aircraft weight is supported bythe air in
the tyre. V V
Therefore the inflation pressure is critical and should becheckd daily and before each Pugh Use
a serviceable pressure gauge (manometer) when checking tyre pressure.
i. Causes excess flexing of the tyre which generates htt and damages the tyres for repe
excess flexing., V V
30
ilL. This causes the un even wear on tyre; with shoulders wearing first
iv. Tires cai creep or slip on the wheeLduring braking; valve sterns on tube-type tircs can
damaged or sheared off and the tire, tube or complete whel assembly can be damaged
IL.
Ill..
i. check the wear on the tread grooves for traction and strength
ii. check for tread depth and wear patterns since the retraction characteristics of the tyre is seriou
affected when the tread is worn
iii. If the tread is worn only to the point that the tread reinforcement is showing, the tyre can be
retreaded but if it is worn into the body plies, then it has gone too far to be saved.
v. Some aircraft are made with some marker e bar when the wear reaches the marker tie b
vi. Some military supersonic aircraft.tyres replacement is determined by the number of landings.
- Defective brakes
- Damaged strut
-k
. . k L&-
Expose plies will call for tyre replacement #& k14 .Zyre hydroplaning (Aquaplaning) L . -
(1CJ - d
-i \ t\
Burns on the tread all cnll for replacement of the tyre, these are caused by hydroplaning This
hydr planning is caused by tyre braking on the wet run way and the tyre comes in contact with
the surface only at one local area.
Tremendous amount of heat is developed at the point of contact and burns the rubber-replace th
tyre
Tyres which have come into contact with oil or grease, should be washed with alcohol, then soap
and Vv dried thoroughly.
Nylon tyres will develop temporally flat spots under static loads.
H N
a.
32
No repairs are permitted except by approved repair station V
... The ngineers job is to give primarily judgment as to weather is repairable or not.
l3reaksdueto flexing V
Heat damage V
There is however no limit to the number of times the tyre may be retreaded, provided the carcass
has n suffered any of the above damages.
Retread-
Retreading is the process of renewing the trad products of the tire allowing the casings to be i
multiple times. V
Tile crown and shoulder rubber of the tyre is replaced and cured in special designed mold.
Remould (Remold) V
This is a term used where the tyre is similarly probessed but cured in a mould similar to that in
which th lyre was originally made.
Up to 10 remoulds have been canied out on specific Tyres with only 10% decrease in strength
The process involves buffing where by the amount of rubber is removed on a Buffing machine
and this operation provides the opportunity for further inspection of hidden defects.
Recapping-
This is a general term meaning reconditioning of a tire by renewing the tread, or renewing the
tree It on or both side walls. V V
1. TOP CAPPING V
2. FULL CAPPING
A retread tyre will be indicated by R and the number of times it has been retreaded will be
indicated by a flgur E. R3. Third time retread shown on the side wall.
Markingsare molded into therubber surface during manufacturing an reniain there throughQut
the tires life.
Markings.provide information that describes the tire, its design capabilities, manufacturing
information, and certification.
Tire Markings will vary depending on the market application, whether bias or radial, and reflect
Aircraft tyres have markings imprinted on their side walls for identification purposes.
Ply Rating (PR) for a given size is an index indicating the maximum load rating in relationship
with the inflation pressure..
NOTE:
Ply rating: .
This is an index number. It may not indicate the actual number of casing plies applied inthe tire
construction.
Load Rating:
This is the maximum static load for a tire, approved by a standardized body, at rated pressure.
The rated inflation pressure is often provided for an unloaded tire (without any deflection).
Inflatiort pressure is given in Bars or Pounds per Square Inch (psi) (1 Bar 14.5 psi).
Specfied Service In/lation Pressure is required for a tire, at maximum aircraft load, to maintain
the
It is determined by the airplane manufacturer and not branded onto the tire.
A loaded tire;
Will deflect and reduce its internal volume which increases the inflation pressure about 4%.
Speed Rating
This is the maximum allowable speed for which the tire is certified speed ratings are given in
miles per
Molded skid is the depth of the center grooves and is molded into the tread rubber during
manufacturing.
This is used for some radial and bias tires to provide the actual construction.
34
N Nylon
12 Casing plies
1 Breaker ply
Modification A
F Fabric
2 reinforcing plies
Modification A
Serial Number
The Michelin Serial Number also provides the fabrication plant and date.
1211C025
[iascitfth
UExle;1for2Ofl)
Lthe1 e was
1211ROQ025
Customer narn.
Part number
Retn ad level
Serial number
Speed rating
Loading in pounds
Modficatio stare
Date of retread
Ply rating
Type of retread
Manufacturer
Part. Number
Serial Number
Date of znanufacture
Speed rating
Size
Ply rating
Type of tread
Load rating
Load Rating
4. TYRE SLIFPI4GE/ CREEP MARKS (use contrasting colours like white, red or orange)
A! RCRAFT TUBES
A great number of aircraft tubes ranging from some of the small type III which is 5.00-5 up to
large VII which is 56 x16 are of the tube type.
35
C.C2is the Federal Administrtio Agcndy (FAA) TechnicaL Standard Order (TSO) uscc to
define 1h mmii .irn performance sandrrds for aircraf tires
o ETSO-Cd2 is the Euroean Aviati6 Shfet Agency (EASA) equivalent of the FAA TSO-C62. Ii
is al used to define the m?nimum performance standards for aircraft tires.
This is unique manufacturer identification for each aircraft tire size/ply rating/speed rating.
Example:
IS ( Vt4CY \
Retread markings:
a.
b.
C.
.d.
e.
f.
g.
h.
1.5
J.
k.
1.
U.
n.
0.
If the tube is too small, its splices will be over stressed and it will be weakened.
TUBE_INSPECTION: V
a. elasticity
b. cracking V V V
c. chafing V
When considered economical, spot repairs. can be made to take care of the tread injuries such as
c ,snags etc.which are not more than 25% of the actually body plies of the tire. V
- Vulcanized spot repairs are also allowed to fill in tread gouges that do not go deeper than tread
rubber and do not penetrat the cord body (fill with dough compound) is allowed
d. Avoid agents like oil, grease, fuels, acids steam pipcs, humidity and any other hydrocarbons
c. Keep avy from source of ozone e.g. fluorescent lights, electric motors, battery chargers, elect:
37
Ozone freaks the molecular bonds, degrading the nibbcr and causing cracks.
a Store tyres vertically on racks with flat surface which is 3-4 wide
e. Tyres can be stacked horizontallyon level ground limiting the height to 3-4 tyres depending c
size.
Storing tubes;
Tubes can also be dusted with talcim powder nd wrapped in heavy paper or scaled plast bags.
Tubes can also be stored in their appropriate size tyres dusted with talcum powder and inflated
just enough to round them off.
Before mounting a tire with a tube inside, always remove the tube from the tire and inspect the
inside of the tire to avoid foreign material which could cause irreparable damage to both the tire
and tube, if not removed.
d.. If tires become contaminated, wash them with denatured alcohol and then with a soap and
watet
solution.
f. The surface of the tire rack on which the weight of the tire rests should be f1a and, if possible,
71o 10cm (3 to 4 in) wide to prevent permarcnt distortion of the tire.
g. When tires are stored for long term (approximately 1 year or longer), it is recommended thai
tires be rotated periodically to prevent distortion in the ttead area.
If tires must be stacked on top of each other, sidewall to sidewall, they should not be stacked fo
more than 6 months.
SHELF L!1E
Tyres and tubes may he kept in storage for up to seven years from date of manufacture but it is
advisab
to limit the stock so that the storage life should not exceed four years.
After seven years tyres should be returned to the manufacture for assessment.
1. WARNINGS:
Aircrt tires must always be inflated with a properly regulated inflation source.
RguIata tha supply line to a pressure no 9reater than 1.5 times the opc-rati inflatia pressure.
38
2. WARN1NGS:
Use a suitable irflation cage when inflating newly mounted tire whc (Ew) assembly.
Any damage to the tire, the wheel, and whl bolts or tmproper proccdre, may cause the
tire/wheel assembly to burst during the inflatiort proccs, wftic may result in serious or fatal
injury.
3. WARNING:
Do not use a mounting lubricant with radial-constructed tires. In-service tire/wheel slippage may
result.
4 WARNING:
5. WARNING: -
The label can cause damage to a tube and result in loss of inflation pressure.
6. WARNING
A used tube will grow in service and may be too large to use in a new tire. a tube that is too large
may cause a fold or crease, which could develop into a split that will cause the release of pressur
Aircraft tires can be expected to grow as much as 12% in service.
In addition, tubes are manufactured slightly smaller than the tire cavity to prevent folds and
wrinkles at installation.
Combining both growth factors, a used tube may be as much as 25% larger than the original si
The excess size of a used tube may cause a fold or crease.
7. All michelin radial aircraft tires are of tubeless design, do not use a tube in an aircraft radial
tire. Do not mount a Michelin radial tire on a tube type vheel, improper assembly may cause
damage the tire.
Pressure gage
Bead Seater
Bead breaker
9. Confirm that the 0-Rings are of the proper material, as specified by the wheel manufacturer for
the intended application and temperature conditions.
Use a new 0-Ring scat with the correct part number when mounting a tubeless tire.
1 0. When aligning the wheel halves, be careful not to damage the 0-ring in the wheel base which
seals the wheel halves, a damaged 0-ring may allow the assembly to lose pressure.
1. It is normal and acceptable to see a balance pad attached to the interior of some aircraft tires.
39
This pad is applied at the factory and brings tire balance within industryand regulatory siandar
Do not confuse this pad with a repair. ..
2. Some wheel manufacturers mark the light spot on each wheel half. (Refer to the wheel
manufacturers Component Maintenance Manual.)
Wheel halves are assembled with these light spots approximately 180 degrees apart.
13. Align the red balance mark on the lower idewall of the tire with the heavy spot on th heel,
unless otherwise specified by the wheel manufacturer.
NOTE: The red balance mark on the lower sidewall of the tire indicates the light point of the t
balance. The red dot is not required on all tires
14. A properly balanced tire/wheel assembly improves the tires overall wear characteristic In
addition to severe vibration, an unbalanced assembly will cause irregular and localized trea wear
patterns that can reduce the overall performance life of the tire.
1 5. -In the absence of specific whcel markings, align the tires red balance mark with the wheel
inflation valve.
16. In the absence of a tire halance.mark, align the tires serial number with the wheel inflation
valve or wheel light spot.
17. The inflation pressure souice should be located 10 meters (30 feet) away from the saf cage
with a valve, regulator, and pressure gauge installed at that point.
I 9. Serviceable tire/wheel assemblies may he transported fully, pressurized in the cargo arc
an aircraft.
20. Always approach a tire/wheel ascmhly mounted on u aircraft from an oblique angle
(direction of the tires shoulder).
21. Confirm that the pressure required is specified for weight on wheels or with the tire
unloaded. (The tire/wheel assembly is not installed on the aircraft or the aircraft is on jacks.) J
loaded tire will have an inflation pressure 4% higher than when unloaded (loaded pressure =
22. Tires operating on the same axle or bogie should be operated at the same pressure 5 When
tires are operated at unequal pressures the tire with the higher inflation pressure will ca greater
load. This can cause shorter-life on both tires due to casing fatigue or abnormal wear.
1. TAXING
The tyre damage can be prevented by proper handling of the aircraft on the ground during taxi
Avoid chunk holes on the run way or other foreign objects on the run way can reduce tvre dan
Taxing speed should be kept to a minimum and for aircraft not equipped with nose wheel slee
the taxing run c-an be kept at 25mph.
All personnel should take tii ramps, parking area, taxing strips and runways clean and cieare all
objects that might cause damage.
Result of overheating is normally ir-dicated tackiness and deposit of tyre wiil adhere to whe fIai
and bead seats.
40
. Loqger runs on takeoff (take offruns) and landing (landing runs) are subjecting tyres o rnoie
abrasion from braking, turning and pivoting.
Severe use of brakes can wear flat spots on tires and cause them to be out of balance, rnakn p.
mature recapping and or replacement.
avoiding proInged application of brakes can reduce on tyre wear and damage
prolonged lyre tread life can also he achieved by care full pivoting Of the aircraft(reducing on
sliarp turns)
Tyre damage at the time of landing can be traced to errors in judgment or un fore seen
circumstances.
Delayhig brakes until the aircraft is dfiniie1y settled into its final roll an also reduce o
AnQthcr causeof tyre damag.a.ncl wear is the condition of the runways, taxing strips, ramps au
These if poorly maintained can cause tyre damages and excess wear
. FYURQ PLANNING
Hydro planning will occur when the aircraft tyres loose contact with the taxi or run way surfac
generally because of film of water between the tyre and the surface.
The result is complete loose of steering capability, controllability, and braking action of the
aircraft.
V When this siruatioi: happens, xtrene heat is built up in a highly localized area of the tyre Vhd
There are tyres specially designed to minimize liydro-planning and this is by proper design or
placement of the grooves in the tread of the tyre so that the Sater can pass under the footprint.
the tyre and the tread can contact the ground.
Some runways of modern construction have cross cuttings to purposely reduce the danger of
hydro-pianning. V V
This again has a draw back in that this kind of cross cuttings create ridges which cause chevron
type of cuttings on the tyre tread-especially with high pressure tyres used on jet aircraft.
Some tvrs for small aircraft are manufactured with a. valve in the side wall.
This kind of design eliminates the need for machining the wheel to take conventional valve
40
Severe use of brakes can wear flat spots on tires and cause them to be out of balance, rnkn p.
mature recapping and or replacement.
avoiding prolonged application of brakes can reduce on tyre wear and damage
prolonged lyre tread life can also he achieved by care full pivoting Of the aircraft(reducing on
sliarp turns) r
Tyre damage at the time of landing can be traced to errors in judgment or un fore seen
circumstances.
Delaying brakes until the aircraft is dfipitely sttled into its final roll an also reduce o
VV - V
Anthcr causeof tyre damage and wear is the condition of the runways, taxing strips, ramps au
cthr paved suriaces
These if poorly maintained can cause tyre damages and excess wear
V V Eliminate loose objects like bolts, rivets, tools, gravel, etc. from th ,rufl Ways.
. FYURO PLANNING V
generally because of film of water between the tyre and the surface.
The result is complete loose of steering capability, controllability, and braking action of the
ircraft..
V When this situatio: happens, xtrerre heat is built up in a highly localized area of the tyre :d
There are tyres specially designed to minimize liydro-planning and this is by proper design or
placement of the grooves in Il-ic tread of the tyre so that the water can pass under the footprint.
Some runways of modern construction have cross cuttings to purposely reduce the danger of
hydro-pianning. V
This again has a draw back in that this kind of cross cuttings create ridges which cause chevron
type of cuttings on the tyre tread-especially with high pressure tyres used on jet aircraft.
Some tvrs for small aircraft are manufactured with a valve in the side wall.
This kin.d of design eliminates the need for machining the wheel to take conventional valve
41
Inflation as well s checking air pressure is accomplished by inetirgnedle through the rubi idewli
waive similar to the way footballs are infiated.
-. This has a rubber stem and a rubber base cured to the outside surface of the inner tube It is
similar to auto mobile tubes vales
Replacement of these valves can be done by gas service station so long as they have the right for
replacement.
ephe rubber base of this valve can be cured on top of the tube or may be cured into the tube.
rmi riOUrriNG
Tubeless tyres -
Most modem aircraft split type wheel which makes it easier to mount the tyre than the single
piece oi detached flange type.
. heins1iing tubeless tyres. care must etaken and manufadtures service instruction mi
- CJ.earing agent
b. The tyre is inspected, wheel also inspected to ascertain that there are no nicks, cracks scrat
especially in bead seat area and also the bead of tyres is safe
Check the grooves for the 0-ring seal between the wheel halves (hubs)
Check to ascertain that the balance weights installed during manufacture are secured in their
locations
42
-d. Place the in board half of thewheel on a flat surface. avoid scratching surfaces
side walls -
- Apply a little bit of talcumto the toe or inner edge of the bead to help the bead scat
Lubricate the 0-ring seal.with.saine grease for the bearings and carefully seal it in tit5
groove.
c. Carefully place the tyre over the iiboar wheel half which was placed on the flat surface
- Ensure that the. tyr,e light, point (red dot) is adjacent the wheel valve er any other rklark to
indicate heavy point of the wheel.
, - At this time place the., outboard wheel valve inside the tyre and line up the bolt holes.
f. apply soi.ie ant-seize compound si,ich as lubtork to the bolt threads and washers and bcarin
surfaces of the nuts.
g; -Drav all the nuts.up.in a crisscross fashion to one half of the reuired torque
- . Use a serviceable torque wrencl to. go back and bring all the nuts to full req torque.
1:.:. place the wheel assembly in a.safety cage nd use clip on chunk to inflate the tyre graduall3
- Adjust thc pressure regulator to the recommended lyre pressure to avoid high. pressure rush.
- Watch to ascea.in tha the beads seat against tile wheel flange (bead area)
NOTE
Nvloi tyres stretches when they are initially inflated, allow them to remain for 1 2hrs to 24hrs
with no 1 applied.
1f.eprssur.e lose exceeds 5%: jfl .any;2hr .rerld, .the. the wJieei assembly should be .aker
further examination. . . .
Tube-type tyres
Before mouating a tube-type tyre,on the wheel, be sure that both the tube and the tyre arc correct
for thai. installation.
- inspect the wheel for corrosion, scratches and restore any protective oxide film is removed
(use zinc chromate primer)
-. clean bead seat area with damp cloth socked in isopropyl alcohol
b.: Glean the inside of the tyre and ensure that there are no foreign objects
- Dust with talcum powder
. . , - insert the tube into the tyre with valve,sticking. out on the side of the tyre having th
serial number
c. Inflate, the tube just enough to round it off and adjust.it so that the yellow mark on the tube
.ndieatng the heaviest point aligns, with REP DOT Ofl tile tyre indicating the right point.
43
If the tube has no mark, then assume that the valve is the heayy point.
Install the tyre and tube on the outboard vtheel half so that the valve sticks out through the h
iuthe. wheel. (a bit of talcum caibe usd around the toe of the bead to help U: slide ovet the wheel
and seat itself)
c. Now you can place the in board half of the wheel in he tyre, be sure the tube is not pinched
- Lubricate the bolts with anti-seize compound and tighten the nuts criss-cross fashion one half
of the required torque.
- Go back and bring all the nuts to.the recommended valve of torque load. (if the whet
have L impression stamped on the flanges, then they should be 1800 apart.
- Put the tyre in a safety cage and rising a chip-on chunk, gradually bring the air press
to the recommended valve to seat the bead and then deflate the tyre. Re-infiateagair the
recommended pressure.
Note
This infjate cefIate infate procedure allows the tube straighten itself outside the tyre and
this w remove any wrinkles from the tube.
- The air pressure may drop after initial inflation.beeause the plies stretch and at the same time th
may he air trapped betweenthe tyre and the tube
- This air will be out with the first 1 2-24hrs and this pressure can be adjusted to the right vakbL.
TYRE R4LA4CG
Tyres or wheel assemblies are always balanced to reduce vibrations which are annoying
especially dur
takeoff.
Place the wheel on the shaft on the balancing stand and allow the wheel to rotate.
Tyres and wheel assemblies are counter balanced with tet weights unti1 the assembly is
balanced.
Then install the correct amdunt of weigMonthe wheel at the loationidentifled by the test weight.
The width -of the mark represents the maximum circumference iovemen permitted with tubed
tyres
COLD TYRE
A coId tire is generally defined as a tire which is the same temperature as the surrounding air
(ambient temperature).
That is, one that has not rolled (taxied or takeoff/landing) for a minimum of three (3) hours.
When checking tyre pressure at ambient temperature, any tyre which is more than 10% below
loaded inflation pressure should be rejected together with comparison of the tyre on the same
axle. Any tyre between 5% -10% below loaded inflation pressure should be re-inflated to correct
pressure a then checked the next day, and if it is more than 5% low, the tyre should be rejected
HOT TYRE
A hot tise is one that has rolled (taxi) under load on the aircraft and has not been allowed to
cool to
ambient temperature
It may be necessary to check the tyre pressure which is still hot after landing.
The pressure should be checked and compared with others on the same leg
44
Any tyre pressure cf 10% or more below the maximum recommended on the same leg should be
int to maximum pressure, hut should he removed if the same loss occurs during the next check.
AIRCRAFT BRAKES
Brakes must be efficient enough to slow down the aircraft by reducing the rolling sped as
required by the p1k They must develop sufficient force to stop the aircraft in reasonable distance
by absorbing its kinetic energy (c aircraft) and dissipating it inform of heat.
They roust he able to hold on the brakes by use of parking brakes using hand brakes so as to
avoid inadvertenU movement of parked aircraft.
2. PNEUMATIC POWER
3. MECHANICALLY OPERATED
1!AJOF CMPONTS OF THE ERKE SYSTEM
4. Brake lines
c,.,- .k
Powered aircraft brake use hydraulic or pneumatic power from the main aircraft power.
5. CARBON BRAKES
45
The mostpopuiar.of fixed disc brake is the Cleveland and which is bolted to the inside wheel half
It is held for braking action by a piston or pistons installed in the brak cylinder.
The floating disc brake is made of forged steel and has a smoOth surface keyed by steel disc
drive key as to. rotate ith the wheel
The disc is free to move in and out enough to prevent it binding as the brakes are applied. Brake
linings were formerly made of asbestos compound, but because of manufacturing hazards
associated with asbestos, modern brake linings are manufactured in form of other friction
materials
Jaferia!3 of construction
The brass and copper adds or gives the exact required friction characteristics
In order to give the lining the required strength, the following can be done.
NOTE
When installing the linings be sure that any letterings or steel cup is away from the disc and the
srnoo side should be next to the disc (see fig 10-36)
5. Lightweight
when it is necessary to increase the capacity of these single dis brakes additional cylinders and
lining pucks may be added (see fig 10-32 ) and pads
Modem single disc brakes have automatic brake adjuster (see fig 10-37)
The purpose of the adjusters is to maintain the gap (spacing) between the brake linings and disc
throughout the life of the brake
Each time the brake is applied and released, the return spring pushes against the head of pin
which pus the piston until the two contacts
Regardless of the wear, the same travel of the piston will be required to apply the brakes
Maintenance of single disc brakes may include bleeding, operational checks, checking lining
wear, checking disc wear or damage and replacement of work lining.
A bleeder valve (screw) is provided on the brake cylinder for bleeding the brakes
a. Checking braking action for each main wheel they must have equal braking action
46
c. When brakes are released, brakes should release without any evidence of dragging.
Dual disc brakes are used on aircraft when more braking friction is desired
It is similar.to single-disc brake except that. the two rotating discs are inthlled because of one.
They are heavy duty brakes designed for use with power brake control valve or power boosted
master
cylinders
In order to increase friction area more discs were adapted, added to form a stack
The stack is keyed to the torque tube rigidly to the under carriages strut.
The alternatng rotating disc were keyed to rotate with the wheel
Application of brakes by hydraulic pressure would force the disc together to provide powerful
and smO
braking action.
The braking force is provided through a series of pistons arranged around the brake unit
: Automatic adjusters are installed to give correct clearances between the rotating and stationa,
Modern multi- disc brakes use S!NTERED COPPER AND IRON BASE FRICTION materials
bonded to the steel rotating disc.
Automatic adjusters compensate for the disk wear each time the brake is applied.
This is,a multidisc brake of modern version used on wide range of medium and heavy aircraft
axle
The stators, back plate, pressure plates have brake linings riveted on them.
The stators have brake linings riveted on both side and back plates have linings only on one side.
Automatic adjusters are threaded into equal spaced holes located in the face of the carrier. The
purpose of the adjusters is to compensate for lining wear by maintaining affixed running cleanti
with the brake in the off position.
Each adjuster is composed of an adjusting clamp, return spring, sleeves nut and clamp holding
down assembly.
The pressure plate and the back plate are non -rotating plate and fitted over the stator drive
sleeves The backing plate is the last unit in the assembly and has linings riveted on it on only one
side.
When the brakes are applied, the pressure plate moves towards the rotor, the washer moves with
the pressure plate causing the string to compress.
As the piston travel increases and on the pressure plate moves further, the linings then comes
into conta with the rotor segments. as the linings wear, the pressure plate continues to move and
eventually come into direct contact with the adjuster sleeve through the adjuster washer.
47
At Ibis point no further force is applied to the spring, additional travel of the pressure plate
caused the lining war will force the adjuster pin to slide through the adjuster clamp.1
When the brakesare released, the return spring forces the pressure plate to return until it bolts
onthe shoulders of the adjuster pin.
As this cycle is repeated during braking and release of brakes, the adjuster pin will advance
through th adjuster clamp due to lining wear but the running clearance will remain constant.
The segmented rotor disc brakes are heavy duty brakes adapted for use with high pressure by
hydrau system.
This is also one of the recent developments of multi-disc brakes type which uses disc made of
CARBO
a. Light weight V
a. Frame
b. Expander tube
c. Brake block
d. Return spring
e. Clearance adjuster V
It contains a metal nozzle through which fluid enters and leaves the tube.
Brake blocks are made of special brake lining material asbestos compound.
The brake blocks are held around the frame and are prevented from circumferential niovemen
the torque bar
Some expander tube brakes have clearance adjusters consisting of a spring loaded piston actin
behind the neoprene diaphragm
48
. When the fluid pressure is less than th spring tension, the clearance adjuster closes off the pass
ihtheinletmainfold.
The tension in the spring can be adjusted by tu.rning the adjusting crew left or right to decrease
increase.
For brakes equipped with adjusters, clearance between the brake block and the drum is usually s
to a minimum of 0.002- 0.015 but exact setting will depend on the particular aircraft.
A dvan (ages
1. Lightweight /
Applicable on large & small aircraft e.g. (Piper super cub, Boeing B-29) & others
2. POWERBRAKES
3. BOOSTED BRAKES
Independent master cylinder fig 5-12 and fig 1-fl and fig 5-16
Earliest drum and shoe brakes were mechanically operated by a flexible steel cable pulling on a
leze inside the brake.
This lever actuated a cam to move the lining agains the drum
A long lever which, if pulled straight back, applied back and to one side it applied only the brake
on ti side- this system gave pilot some degree of independent braking.
TQ increase the pressure applied to the brake linings, hydraulic cylinders soon replaced the
mechanical type.
Individual master cylinders were used to.apply pressure to the brake cylinder inside the wheels
when th pilot pressed on the brake pedals or pulled back the parking brake lever.
This is a hydraulic cylinder connected to the pilot pedals, one for each pedal and provides
independent braking, equal braking or differential harking.
49
2. Piston
3. Piston spring
6. Body cover
8. Compensating sleeve
9. Set screw
When the brakes are applied, the piston moves down and a small quantity of fluid is displaced
from ti
cylinder to the reservoir until the lock o- seal contacts the piston.
The piston moves down with the compensating sleeve forcing fluid from the cylinder to the
brake uni
(brake cylinder)
When the brakes are released, the piston return spring moves the piston rod up
The o- seal remains in contact with piston because of the pressure applied by the piston spring.
The fluid returns with the piston from the brake unit.
When the compensating sleeve contacts the cover boss and the piston rod continues to move up a
furt
0.040
A small quantity of fluid is displaced from the reservoir to the cylinder during the final
movement Any increase in the volume of the system due to wear of the brake friction pads is
allowed for by the reservoir topping up the cylinders when the brakes are off and lock o-seal
open.
Any pressure or excess volume of fluiddue to expansion is relieved through the compensating
port which is to the reservoir. Compsiting ports V-Shaped
This will prevent the master brake cylinder from locking or causing brakes to drag.
1. Permits the brake to be released by allowing th flow of fluid from the brake unit to the reserve
3. Replenishes the brake line as required due to brake line wear or any small leakage inn the syst
The parking brake system is by ratchet operated handle-connected to the brake master cylinder
by cab linkage.
i. Fully depress the rudder pedals (brake) and iull the parking breakllevcr fully out an twist ant-
clock wise to vertical position, the piston will lock.
ii. To release parking brakes, apply toe pressure more thati the initial application and t the handle
clock vic nnd nnch Cii1!r
50
iii. : Application of pedal before and after prevents overstraining the cable.
- As a ride, power boost brakes are used oi aircraft 1/tat land too fast to employ the iirdepeiidei.
brake System, but too light to require power brake control valves.
- The action of boosted brake master cylinders is similar to the ordinary master cylinder except in
the following ways; V
ii. The toggle mechanism operates a. spool valve which opens to permit the system pressurc
assist the pilot to move the piston.
- As the pilot applies toe pressure, the piston is pulled down, sending the fluid pressure to the
bra]
cylinder: V V
- The tendency is for the toggle mechanism to straighten out moving the spool valve down vars
- Further movement of the piston will cause the valve to open the lower port and allow flowing
LC the top of the piston and forcing the piston further down there by assisting the pilot to apply
pressure. V
- When the pressure on the brakes is released the toggle mechanism returns the valve to its origin
position, venting the top of the piston to the reservoir.
- Simultaneously the compensator poppet valve opens to vent(the brakes) to the reservoir and bra
are released (see page 365 for another type of boosted brakes) fig 9-32
- This type is found on large aircraft brake system which cannot be operated by either the master
cylinder or boosted type.
- the pressure to actuate the brake is obtained from the aircraft main hydraulic system
- Because of the weight and size of the aircraft large wheels and brakes are required hence r - tei
fluid displacement and high pressures.
- The following units are fitted to adapt the high pressure of hydraulic system to the special
requirements of the brake system.
2. Accumu(ator V
This stores a reserve supply of fluid under pressure to cater for minor leakages and also to preve
pressure surges or fluctuations. V
These valves are installed in the system to ensure that braking action is proportional to the press
exerted on the brake pedals without there being a build up pressure in the brake line.(controls or
regulates the volume and pressure of fluid which actuates the brakes)
51
/
In a particular design, they are pre-set to Open at 82S psi and connect the system to retu
line
. Shuttle valve
The purpose of shuttle valve is to isolate the normal brake system from the emergency system.
These are fitted to reduce the main system pressure to a value more suitable for braking action
(pressure reducing valves).
7. Antiskid system:
The pilots pressure on the rudder pedal (toe-pressure) depresses a plunger on the brake contro
valve and opens a spool valve which directs hydraulic pressure to the brakes.
The dc-booster valve operates on principle of differential area to reduce the pressure going to t
brakes.
The de-booster has a valve which opens to replenish the brake line if there should be a leak
Lock- out de-boosters operates on the same principle-except that tO replenish the brake line, a
handle must be pulled manually.
An ant skid system is fitted to prevent lock up of wheels which would cause loss of direction
and braking control.
The ant-skid system senses wheel deceleration and regulates the amount of fluid pressure to th
brakes so as to maintain optimum braking action under all conditions.
Optimum braking friction is reached when the speed of the tire is slightly less than the speed c
aircraft causing the tyre to slip a little without skidding.
The friction between the tyre and the run way sur.face is affected by the type of the surface,
condition of the surface and condition of the tyre.
The purpose of a wheel brake is to bring a rapidly moving aircraft to a stop during ground roll.
Modern high speed aircraft usually have more than one wheel on each side, and all of the braki
on one side are controlled with one pedal
With this arrangement, the pilot has no way to know when one of the wheels begins to skid so
corrective action can be taken to release locked up wheels, the tyre is likely to blow out and co of
the aircraft can be lost.
When the aircraft touches down on water covered runway and the pilot applies brakes, the fricl
on the run way surface is so much less than that generated in the brake that the wheel locks-up
the tyre hydroplanes down the run way, supported on the surface of water in much the same w.
Atwater skier is supported.
All braking action and directional control is lost for a hydroplaning wheel
If the break pressure is held constant after the slip starts and the whel begins to decelerate, th
brake friction will rapidly increase to a point that a wheel will lock-up the tyre will skid over 11
run way and produce very little braking.
52
With the design of the ant skid system, it is ensured that optimumbraking pressure is
- applied under any prevailing condition and restricts maximum pressure to just below the value
that would cause the locking of the wheels.
1. They must be a form of wheel speed sense-that can defect a change 1. the rate of deceleration,
2, A signal for the pressure to be released before the wheel gets deep in; its skid, also valve to act
fast enough to prevent all of the pressure being released before the next application of the brake.
Operation of anti-skid system:
When the pilot wants to stop the aircraft in the shortest distance possible, it is necessary to
depri the brake pedals all the way to call for maximum braking.
All of the brakes receive maximum pressure but if any wheel should start decelerating at a rate
which would indicate an impending skid, the pressure to brake is dumped into the system
retulT
manifold.
At this time the control circuit measures the amount of time required for the wheel to spin b and
then applies a slightly reduced pressure to the brake a pressure determined by the time required
for the spin up.
if this reduced pressure cause a skid to begin to develop, enough of it is released to allow the w]
to spin back-up
some pressure is maintained in the wheel brake cylinder, however just enough to prevent the
pressure plate from moving all the way back
the application and release process continues with progressively decreasing pressure applied un
the wheel is held in the slip[ area, but not allowed to decelerate fast enough to produce a skid
It produces a proper amount of braking for any run way surface condition, with the pilot having
only to call for maximum braking.
When the aircraft is slowed down below approximately 20mph and there is no further danger ol
skidding, the ant skid system automatically de activates to give the pilot full control of the brak
for maneuvering. And parking. I
As a modern system, the ant-skid system has built in test circuit and at the same time in an ever
failure of the system it may be deactivated by the pilot to give him normal braking but no ant-si
protections
It is a variable reluctance AC generator which is driven by the aircraft wheel and it senses the
wheel rotational speed.
The faster the wheel turns, the higher the frequency of induced current.
The signal from the speed sensor is conveyed to the control box.
2. Control box
This converts the ac signal to de signal which is generated by the wheel speed sensor
i. Developing skid..
It analyses all it reads, and then send an appropriate signals to solenoids in the skid control
valves to a required.
3. Control valves
If there is no signal (because there is no wheel skidding) the skid control valve will have no ef
on brake operation
If a skid develops , either slight or serious a signal is sent to the skid control valve solenoid
The solenoid action lowers the metered pressure in line between the metering and the brake
cylinder dumping fluid into the reservoir return lime whenever the solenoid is energized and
relaxes the brake application.
The pressure flow into the brake lines from the metering valve continues as long as the pilot
depresses the brake pedal, but the flow of fluid is routed to the reservoir instead of to the whee
brakes.
The system is designed to apply enough force to operate just below the skid point and this give
the most efficient braking
The pilot can turn off the operation system of anti-skid system by switch in the cockpit, a red h
will come on when the system is turned off or when there is failure.
Normal skid control comes into play when the wheel rotates slowly down but has not C
to a stop
When this happens the wheel sliding action has just began but has not yet reached a ful.
scale slide
In this situation the skid control valve removes some of the hydraulic pressure to the v..
This permits the wheel to rotate a little faster and stop its skidding.
The skid detection and control of each wheel is completely independent of the others
The wheel skid intensity is measured by the amount of wheel slow down
54
It will occur if the normal skid control does not prevent the wheel from reaching a full skid. To
release a locked wheel skid, the pressure is bled off longer than in normal skid function.
This action gives the wheel time to regain speed. The locked wheel skid control is out of action
during aircraft speed of less than 15-20 mph.
3. Touchdown protection
The touchdown protection circuit prevents the brakes from being applied during landing appro
even if the brakes are applied.
This prevents the wheels from being locked when tFey contact the run way.
The wheels have a chance to begin rotating before they carry the full weight of the aircraft.
a. The squat switch must signal that the weight of the aircraft is on its wheels
The fail safe protection circuit monitors operation of the skid control system.
It automatically returns the brake system full manual in case of system failure and also turns on
the warning lights.
In case of a total hydraulic pressure failure, the emergency system provides a means of
stopping the aircraft during emergency landing
A pneumatic valve located by the pilot and it directs compressed air or nitrogen to the brakes
through a shuttle valve.
When the pilot turns the emergency handle, he is actually adjusting the regulator controls air
pressure to the brakes.
When the handle is rotated in the direction to release the brakes, the air is exhausted overboard.
Rather than allowing compressed air to enter the wheel cylinders, which would cause o:
require the entire brake system to be bled the emergency air may be directed into the transfer
tube. the air forces hydraulic fluid from this tube into the brake system.
Many large transport aircraft e.g B727, A380, A320, MIG-21 have brakes installed on the nose
wheel
. Movement of either left or right brake pedals will actuate the corresponding right or left main
brake.
55
If
b. Check for air in the system check for fluid quantity and type
7V
er
V_,,I ..
VV
When the brak pedals are depressed the differential 1sagto the Vfl gear metering valve first
after this valve is opened continu v fThe braice pedals is directed to the nose gear metering valve
and then to the brakes, nose wheel braking is availabh above I 5mpkfrom straight ahead to
approximately 60 of steering
At this point the nose wheel steering brake, outs off sw t-dcl
,S1VVi r
..
.) e VT
2..
a.
b.
C.
d.
e.
f.
- Ii,)_;
Ckv.
Brake lining wear at a rate that depends on usage, i.e on of landings aitheV degteof braking and
req
Wear on good year brakes is usually determined by the length of the rtim pinf the automatic
adjust
Brakes without automatic adjusters have the thickness of the litiing omared with No. 4driU
VV
V 1...,
The linings musLbe replaced just before they reach this thickness.
multiple disc brakes can be measured by applying the brales the clearance bet the back of
pressure plate and the edge of the brake linings V
alternatively a gauge can be provided for this purpose (see fig 10-57)
Excessive clearance mean excessive wear in brake unit and the unit should be disassembled an
wear of the disc checked individually. V
56 -
Cleveland brake linings should be replaced when they are worn to thickness of 0.100 or
the presence of air in the brake line is indicate by the sponginess Of the brakes
The air must be expelled by bleeding in order to restore the brake effectiveness
.. -When t brake master cylinder is fully released, there is direct passage from the brake cylinder
throghee-mpensator port to the reservoir and this prevents any pressure to build up in the brake
rcausig brakes to drag.
1. Pressure method
Remove the screw from the bleed valve on the brake cylinder
Connect a pressure pot containing hydraulic fluid under. pressure ensure that there is no
V Attach another hose to the masterVcylinder vent and dip the other end into a container f
fluid
Open the valve of the pressure port to allow fluid under pressure from the port through ti
cylinder and break lines out through the reservoir vent into the container.
Watch for bubbles in the container at the reservoir end and a low the fluid to continue
V Close the valve on the port and also close the bleeder screw and disconnect the port.
- V Disconnect the hose at the reservoir and check that;there is sufficient fluid in the reservo
2. Manual
V V In this method, fluid is forced through the brake line from the normal direction and the
press is provided by pumping on the pedal at the master cylinder.
V V V - V Fit one end of a flexible tube to the bleeder valve screw on the brake cylinder and dip
= t Ensure the fluid level in the master cylinder reservoir is kept constant by replenishing thr
V V Open the bleeder valve on the brake cylinder and pump the master cylinder
V V Observe for bubbles in the fluid container and continue pumping the master cylinder until
V bubbles cease. V
V V Hold the master cylinder depressed and close the bleeder valve on the brake cylinder.
V V V Disconnect the horse from the bleeder valve and replenish the reservoir if necessary.
Remove the bleeder screw from the brake cylinder and install a length of flexible hose
Place the other end of the hose in a clean container of hydraulic fliid
Open the bleeder valve and with hydraulic pressure in the proper operating range, very careful
apply the brakes.
Allow fluid to flow to the container until no more bubbles are seen
Close the bleeder valve, remove the hose and replace the bleeder screw.
. The bleeding procedure is not complete until both the main and emergency or backup systems
free of air.
Run the engine and tax the aircraft to ascertain the breaking efficiency.
It is important that reservoir be filled with the right amount of fluid and the specified type
If insufficient fluid quantity is filled it will degrade the effectiveness of the brake and also allo
to enter.
Wrong type of fluid will cause damage to the seals as they will be attacked by incompatible flu
System leakages are likely to occur at threaded connections, past rubber seals defective castin
Simply retightening leaking connections may not solve the problem as aleak may be sign of
internal damage
The correct procedure is to turn off the system and check the leaking area thoroughly
BOLT TORQUE
Check the bolts and nuts for proper torque using serviceable torque wrench
Use a red paint mark across the bolt and nut or bolt and structure
DISC CONDITION
I)
58
AUTOMATIC ADJUSTERS
Check return pin visually for bending or other damage and magnetically for cracks.
TORQUE TUBE
Scratches
Toolmarks
Corrosion
Scratches on pistons
Wear of pistons
CONDITIONS OF SEALS
1. Over heating
Brakes are designed to absorb great amount of heat, but during abnormal operation, rejected taK
off or prolonged hash braking and overheating condition-care full inspection must be carried out
3. Dragging
This is a situation on the brakes to continue holding after pressure has been removed off the bn
pedals
c. Faulty adjusters
ci. Fitting of new linings (disappears after some few rounds of taxing
ii
. Chattering of brakes result from brakes failing to provide smooth action and instead coming on
off generating vibration and noise
Causes of chattering
5. SPOGGY BRAKES
\ c i.-
2. When performing maintenance work which will affect landing gear linkages and adjustments e
exchange of actuator.
2. Check for lights, switches and warning horn or buzzer for proper operation
3. Check for landing gear door for clearance and freedom of binding
4. Check landing gear leakages for proper operation adjustment and general condition
5. Check for latches and locks for proper operation and adjustment