typres Flashcards
aircraft wheels are fitted with which tyres
pneumatic tyres
types of pneumatic tyres
Tubes (light or older aircrafts)
Tubeless
Tyres filled with?
Nitrogen
can support AC’s weight
good at absorbing shock
tyre cover benefits
protects the tyre tube
transmits braking
provides a wearing surface
maintain shape of the tyre
Tyre covers
Covers: made of rubber
Reinforced by Plies - cotton, nylon or rayon cores
Breaker strips
What are breaker strips
**2 narrow plies* *embedded in thick rubber
between the casing and the tread
- absorbs shock
- protect from casing concussion
*
Plies cords
not woven
arranged in parralel in single layers and held by thin film of rubber to avoid chords cutting into each other
Bias cross ply
plies fitted in pairs
chords set at 90 degrees angle to one another
Radial tyres
plies fitted in pairs
chords set from bead to bead at approx 90 degrees to centre line of the tyre
Bead
The casing is retained on the rim of the wheel by interlocking the plies around inextensible steel wire coils to form ply overlaps
wires are copper
rigidly bonding done between wire coils and the rubber
protected on the outside by chafer strips
ply rating
index of tyre strength (not related to the # of plies in the typre)
Tyre region - Crown & shoulder
‘tread’
This is where tread is located
**
tread has **ribbed patters/grooves
for:
1)assist in water dispersion
2)prevent acquaplaning
3)create contact/grip on the runway
Diamond tread
used for all ‘weather patterns’ but not commonly used
Nose wheel is fitted with?
Chine (moulded) in the shoulder area (sometimes on either side of the tyre)
usually for Aircraft with engines mounted in rear fuselage
it helps direct water away from engine intakes to avoid flameouts
Braking and inner tubes
during breaking, excessive heat is generated
this can cause damage to standard inner tube
therefore the tube might have one of these reinforcement bases
- standard
- thickened
- cord
when renewing the tube
must be replaced by the same tube type
Inflation valve
it’s where the tube is inflated
infalation valve is vulcanized to the tube, therefore it cannot be renewed on its own
Inflation valve anatomy
1) fitted with Scrader valve core (non-return valve)
2) The valve is not a perfect seal, so need inflation valve cap (also protects from dirt)
3) Schrader valve is a spring made of brass but stainless steel on modern ones
Tubeless tyres
Tyre size, construction and pressure need to accmmodate
- landing speed
- loading
- landing surfaces
- landing gear construction
4 main categories of pressure
Low
25-35psi
for grass areas
medium
35-70psi
for grass and some medium firm surfaces
high
70-90psi
for concrete surfaces
Extra high
90+psi ..even to 350psi
for concrete surfaces
Tyre contamination
Oil skin cover should be placed on the tyres to protect from:
**especially when parked **or when fluids are being replaced
- hydraulic fluid spills
- bright sunlight
- heat
- dampness
- oil, fuel, glycol
oil, glycol, hydraulic fluids must be wiped off immediately
creep when tyres are first fitted
when tyres are first fitted to a while, they tend to move slightly around the wheel
this is normal and ceases after some time
Creeping in Service
In service, the tyre may tend to continue to creep around the wheel.
Creep a tyre fitted with an inner tube:
- will tear out the inflation valve and cause the tyre to burst.
creep on tubeless tyre
- Creep is less of a problem with tubeless tyres, as long as the tyre bead is undamaged and any pressure drop is within limits.
to prevent creep
mainain correct pressure
Underinflation causes creep
you can check via electonic system monitoring screen in the aircraft
What is Rated Inflation pressure
Pressure specified by the manufacturer
this is based on a cold/unloaded tyre (when tyre not fitted to a plane
once fitted - increase that pressure by 4%
once it’s taxing, landing, taking off - increase that pressure by 10%
what’s the tyre inflated with
Mainly nitrogen
other gases (maximum 5% Oxygen)
Marking on tyres
1) ECTA/Conducting:
shows tyre has extra carbon in the rubber to conduct electricity (provide earthing between aircraft and ground)
2)Size on the sidewalls
Inside diameter - in
Outside diameter -in/ml
Nominal diameter - in/ml
3)ply rating on sidewalls
strength of tyre in ‘PR’
4)Green or Grey dots
Indicate the position of the AWL vent
5)red dot or triangle
indicate the lightest part of the typre
placed oppostie the valve
assist in balancing whieel assembly
6)DRR (in code panel) and ‘REINFORCED Tread’ in sidewall
indicative of the fact that the tyre has a layer of fabric woven into the tread which may become visible during normal wear. This layer must not be confused with the casing cords.
Aquaplaning
caused by wedge of water building up under the tread, breaking contact with the ground
Aquaplaning speed is in NM / HR
=9 x Squar root of Tyre pressure in PSI
**if treat dept is reduced, aquaplan increases **
what is MAT Limits
MAT = Mass, Altitude & Temperature
these may be altered to ensure they comply with the typres fitted
ex: when calculating take off distance with increased speed, it’s important to not exceed the speed rating of the tyres
Tyre damages
Cuts
- replace if cuts show the cords
Bulges
- indicate partial failure of the casing
- Renew cover
**Foreign bodies
**- must not be removed and should be report to maintenance
- need to acertain depth of the cut
wear
replace if tread work to casing covering or
to the base of the marker groove
creep
-Movement of the tyre round the wheel must not exceed 1 in for tyres of up to 24 in outside diameter and 1½ in for tyres over 24 in outside diameter.
-typres must be removed
then tube is examined to see tearing of the valve
-if serviceable, tyre to be refitted and creep marks re-applied.
Treat separation
-when tread portion is detached from the tyre or Burst )this increases load on other tyres, reduce braking efficiency)
FOD - foreigh object damage
possibility of damage to brake hydraullic lines or debris in the engine
to minimize the tyre wear, what’s the speed limit during taxi
40 km/hr
or 25m/hr
overinflation causes wear in -
the crown
underinflation caues wear in
the sholder
Tubeless tyres characteristcs
- Low heating
with Tube tyres, they are at risk of high heating due to the friction between the tube and tyre - low valve fragility
With tube tyres, the valve is connected to the tube and shear can damage the valve.
In tubeless, the valve is connected to the rim so the valve & tyre and independent - lower risk of bursting (#1 & 2)
