Lecture 06   Aircraft Wheels

Lecture 06 Aircraft Wheels


so now coming to aircraft wheels as we all
know that wheels are a very important part of any vehicle similarly in aircrafts they
are an important components of the landing gear system tires are mounted on these wheels
they are use to support the entire weight of the aircraft during all phases of operation
on ground that is during taxing takeoff and landing a typical aircraft wheel should be
of light weight strong and is generally made of aluminum alloy some of the aircraft wheels
are also made of magnesium alloy now during the old days the aircraft wheels
were of single piece construction like we have in the modern automobile wheels but as
time progressed the aircraft tires were improved they were made stiffer so that they can absorb
forces of landing without blowing out or separating from the rim so with improved tires single
piece rim was not possible because stretching of tire would have been a difficult thing
with this improved tires with these improved tires a two piece wheel was developed so you
can see in the diagram the wheel construction the wheel is in two halves
this modern two piece aircraft wheel is generally made of casting or forging from aluminum alloy
or magnesium alloy these wheel halves are bolted together and they contain a groove
at the mating surface so at the groove there is a ma there is a groove at the mating surface
for an oring which seals the rim since most modern aircraft utilize tubeless tires so
in the diagram we can see there is an oring a yellow coloured oring in between this oring
gets into the groove at the meeting surface and is used for sealing the rim so that tubeless
tires can be used in this slide you can see the diagram in the diagram you can see there
is an outer wheel half see this the outer wheel half the inner wheel half there are
two wheel halves the outer wheel half the inner wheel half
we just now mentioned in the last slide an oring in between you can see this the oring
then there is a disc which is attached to one of the wheel half the inner wheel halves
then there are bearing con cones bearing cups and cones on both sides on the outer side
as well as the inner side then beyond the bearings you can see the grease seal rings
and the snap rings to bo to loc lock the grease seals the inner in the inboard wheel half
you can see in the diagram the inboard wheel half these wheels halves the outboard and
inboard they are not identical the main reason for this is that the inboard wheel half must
have a means of accepting and driving the rotors of the aircraft brakes that are mounted
on both main wheels so in the brakes you can see this disc this is mounted to
the inboard wheel half due to this the two wheel halves are not identical they are different
from each other this inner inboard wheel halve will have disc attached to it where as the
outboard wheel half has no provision for this disc the outboard wheel half bolts to the
inboard wheel half to make up the wheel assembly upon which the tire is mounted
so this outboard wheel half is bolted to the inboard wheel half and this together makes
up the wheel assembly on which the tire is mounted the centre boss you can see here in
the diagram in the centre on both the wheels halves this is the outboard wheel half as
well as this inboard wheel half both places you can see there is a centre boss it is constructed
to receive a bearing cup this bearing goes in this wheel half
and bearing assembly as it does on the inboard wheel half so the centre bo boss is constructed
to receive a bearing cup and bearing assembly on both the wheel halves on both inboard as
well as the outboard wheel half the outer bearing and end of the axle is capped to prevent
contaminants from entering this area so the bearing and the end of the capsule axle is
capped so that the contaminants do not enter this area
so what are the inspections we carry out on the wheel an aircraft wheel assembly is inspected
while on the aircraft as often as possible so generally in all the p flight inspections
before every flight we carry out an inspection on the aircraft on the wheels also a more
detailed inspection and any testing or repairs may be accomplished with the wheel assembly
removed from the aircraft so inspections may be with the wheel on the aircraft or removed
from the aircraft so more detailed inspection is done with the
wheel assembly removed from the aircraft now when the wheel assembly is on installed on
the aircraft what inspection do we do the general condition of the aircraft wheel assemblies
can be inspected while on the aircraft any signs of suspected damage that may require
removal of the wheel assembly from the aircraft should be investigated so when the wheel assembly
is there on the aircraft we carry out a general inspection a visual inspection to see that
the wheel is securely attached there is no damage there is no happen damaged on the assembly
now coming to tires and tubes the aircraft tires and tubes the tires may be tube type
or tubeless type they support the weight of the aircraft
while it is on the ground and provide the necessary traction for braking and stopping
the tires also help absorb the shock of the landing and cushion the roughness of takeoff
rollout and taxi operations so the tires they support the weight of the aircraft while on
the ground provide necessary traction for breaking and stopping they absorb the shock
of landing and cushion the roughness of takeoff rollout and taxi operations coming to tire
construction in the diagram you can see a cross sectional view of a tire is given an
aircraft tire is constructed for the purpose it serves unlike an automobile or truck tire
it does not have to carry a load for a long period or of continuous operation so in aircrafts
the tires they do not have to carry load for long period of continuous operation because
as soon as the aircraft gets airborne there is no load on the tire however an aircraft
tire must absorb the high impact loads of landing and be able to operate at high speeds
even if only for a short time so during landing the tire has to absorb high impact loads and
has to operate at high speeds during takeoff and landing both the speeds are high so your
tire should be able to with stand this high impact loads and it should be able to operate
at high speeds the deflection built into an aircraft tire is more than twice that of an
automobile tire in the diagram you can see the various parts have been mentioned here
you can see the breakers this is the tread these are the tire side balls these are the
casing plies you can see these are the casing plies
these are the wheel beads sorry wire beads bead heel this is the bead toe this is the
inner liner you can see here the inner liner then these are the piles so this the cross
sectional diagram of the tire showing different layers of piles this enables it to handle
the forces during landings without being damaged so this tire will help in handling the forces
during landings so that there is no damage on the aircraft
only tires designed for an aircraft as specified by the manufacturer should be used it is useful
to the understanding of tire construction to identify the various components of a tire
and the functions contributed to the overall characteristics of a tire now aircraft tires
are classified in various ways including ply rating whether they are tube type or tubeless
and whether they are bias ply tires or radials so tire classification is by ply rating they
may be tube type or tubeless type they may be bias pau ply tires or they may be radials
tires this is bias ply aircraft tire you can see in the diagram a bias ply tire has the
fabric bias oriented with and across the direction of rotation and the sidewall
since fabric can stretch on the bias the tire is flexible and can absorb loads strength
is obtained by adding plies so the tire is also classified by ply rating the more the
number of plies the more the tire is the more strength the tire has now radial ply aircraft
tire a radial tire has the fiber strands of the ply fabric oriented with and at ninety
degrees to the direction of rotation and the tire sidewall so this is the fabric orientation
is ninety degrees to the direction of rotation and the tire side wall this restricts flexibility
directionally and the flexibility of the sidewall while it strengthens the tire to carry heavy
loads now ply ratings tires plies are reinforcing layers of fabric
encased in rubber that are laid into the tires to provide strength in early tires the number
of plies used was directly related to the load the tie could carry but now a days refinements
to tire construction technique and the use of modern materials to build up aircraft tires
makes the exact number when determining the strength of a tire however a ply rating is
used to convey the relative strength of an aircraft tire a tire with a high ply rating
is a tire with high strength which is able to carry heavy loads regardless of the actual
number of plies used in its construction of plies tube type or tubeless aircraft tires
can be tube type or tubeless tires that are made to be used without a tube inserted inside
have an inner liner specifically designed to hold air tube type tires do not contain
this inner liner since the tube holds the air from leaking out of the tire
bead we will see what is bead the tire bead is an important part of an aircraft tire it
anchors the tire carcass and provides a dimensioned firm mounting surface for the tire on the
wheel rim tire beads are strong they are typically made from high strength carbon steel wire
bundles encased in rubber so in the diagram you can see here this is the bead this is
the bead heel this is the bead toe and the beads they are made of wire they are carbon
steel bundles which are encased in rubber so this bead is an important part of an aircraft
tire one two or three bead bundles may be found on each side of the tire depending on
its size and the load it is designed to handle the bead transfers the impact loads and deflection
forces to the wheel rim so this bead transfers the impact loads and deflection forces to
the wheel rim tread what is tread tread is the crown area
of the tire designed to come in contact with the ground it is a rubber compound formulated
to resist wear abrasion cutting and cracking it also is made to resist heat buildup most
modern aircraft tires tread is formed with circumferential grooves that create tire ribs
so in the diagram you can see these are circumferential ribs you can see circumferential ribs in the
diagram you can see the grooves and these create the tire ribs
the grooves provide cooling and help channel water from under the tire in wet conditions
to increase adhesion to the ground surface so uh the purpose of the grooves they provide
cooling and help channel water from under the tire in wet conditions to increase adhesion
to the ground surface now what are the inspections on tire inflation pressure tread wear and
condition and sidewall condition are continuously monitored to ensure proper tire performance
so during the time when the tire is used almost in daily inspections inflation pressure is
tested tread wear and condition is checked side ball condition is checked these things
are continuously monitored so that proper tire performance can be achieved
inflation tire pressure is checked while under load and is measured with the weight of the
aircraft on the wheels a calibrated pressure gauge should always be used to measure inflation
pressure so in the diagram you can see a pressure gauge has been shown an aircraft tire has
designed to flex and absorb the shock of landing tire pressure should be measured at ambient
temperature fluctuations of ambient temperature greatly affect tire pressure generally tire
pressure changes one percent for every five degrees fahrenheit of temperature change so
we have to be careful at what temperature we are observing we are checking the inflation
pressure generally it is fluctuation of ambient temperature greatly affect tire pressure
now tread condition asymmetrical tread wear may be caused by the wheels being out of alignment
occasionally asymmetrical tire wear is a result of landing gear geometry that cannot or is
not required to be corrected like camber toe in and toe out it may also be caused by regular
taxiing on a single engine or high speed cornering while taxiing see in the diagram you can see
there are various tread wear shown in this diagram you can see this is tread wear on
an overinflated biased tire this is the biased tire cross section shown this is tread wear
on an overinflated bias tire and this is tread wear on an overinflated radial tire this is
the wear pattern has been shown this is the bias tire tread wear and this is the tread
wear on a real radial tire both ov overinflated this is underinflated condition and both tread
wear has been shown on bias tire as well as the radial tire you can see the difference
now in this diagram this is the normal condition this is worn out this tire is worn out this
is under inflation in case if you have been operating your tires under inflation condition
so that wear will be of this pattern you can see the wear and incase your tire is has been
operating in the over inflation condition your wear will be of somewhat like this kind
of thing now flat spot this is the result of the tire skidding on the runway surface
while not rotating so you can see the wear here see this this wear pattern this is as
a result this is the result of a flat spot aircraft tubes a tube is there inside to contain
the inflation air an aircraft tube must be inspected for leaks and damage aircraft tire
tubes are made of a natural rubber compound in order to check the leaks remove the tube
from the tire inflate the tube just enough to have it take shape but not stretch immerse
a small tube in a container of water and look for the source of air bubbles again look for
the sources of bubbles the valve core should also be wetted to inspect it for leaks this
is the normal procedure which we do in our automobiles also so this is just the normal
procedure of checking the tubes now when we assemble the tires and tubes in the diagram
here you can see there is a red dot you can see the red dot here a red dot on
the tire identifies the light side of the tire so this red dot this red dot is indicating
the light side of this tire now this is the tube in this second diagram you can see this
is the tube there a yellow dot or a line on the tube this identifies the heavy side of
the tube so this is this is the lighter portion of the tire this is the heavier portion of
the tube if no mark is found on the tube the valve stem the valve stem is used to align
with the red dot on the tire so incase if there is no mark on the tube
the valve stem is considered to be the heavy part of the tube so while assembling the lighter
side of the tire and the heavier portion of the tube they are aligned so that the assembly
is balanced this will ensure that the tire and tube balance as close as possible before
using the tire balancer and adding the necessary weight on the exterior of the wheel
so this is basically required for balancing the tire and tube assembly by aligning the
lighter portion of the tire and the heavier portion of the tube tire balancing this is
also a normal thing as we do in other automobiles also once an aircraft tire is mounted inflated
and accepted for service it can be balanced to improve performance vibration is the main
result of an imbalanced tire and wheel assembly nose wheels tend to create the greatest disturbance
in the cabin when imbalanced static balance is all that is required for most aircraft
tires and wheels a balance stand typically accepts the assembly on cones the wheel is
free to rotate the heavy side moves to the bottom temporary weights are added to eliminate
the wheel from rotating and dropping the heavy side down so this just as in any other tire
this is normal balancing so here in the diagram you can see a tire balancing patch this is
the tire balancing patch on the left side these are adhesive wheel weights in the centre
and a bolted wheel weight you can see this this is the bolted wheel weight on this in
this right diagram they are all used to balance aircraft tire and wheel assemblies as per
the manufacturers instructions now tire storage an aircraft tire can be damaged
if they stored improperly a tire should always be stored vertically so that it is resting
on its treaded surface horizontal stacking of tire is not recommended storage of tires
on a tire rack with a minimum three to four inch flat surface for the tread is ideal and
avoids tire distortion now tube storage and inspection an aircraft tire tube should be
kept in the original carton until put into service to avoid deterioration through exposure
to environmental elements if the original carton is not available the tube can be wrapped
in several layers of paper to protect it alternately for a short time period only a
tube may be stored in the correct size tire it is made for while inflated just enough
to round out the tube application of talc to the inside of the tire and outside of the
tube prevents sticking remove the tube and inspect it and the tire before permanently
mounting the assembly regardless of storage method always store aircraft tubes in a cool
dry dark place away from ozone producing equipment and moving air so these are the general storage
steps for the tube with this we end this module of aircraft landing gear system so in this
module we have seen the different types of landing gears the inspections the tires and
the tubes thank you

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