AGK Systems - Wheels, Tyres and Brakes Flashcards
What is Ply Rating?
Indicates tyre strength
Tread
Rubber. Provides grip, expels water
Tubless
Internally airtight, no inner tube. Lighter & runs cooler
Bias (or cross-ply)
Plies laid in pairs. Adjacent at 90°
Radial
Plies are laid from bead to bead
Retread
New tread heat bonded onto old carcass
Tubed Tyres
Use an inner tube with an inflation valve attached to it which is fed bout through a hole in the wheel
What is Tyre Creep?
Only relevant for tubed tyres
Sudden accelerations cause the tyre to slip around the wheel
Creep is greatest just a tier a new tyre has been fitted. Excessive creep damages the inflation valve
Creep is monitored with creep marks
Tyre Speed Rating
Often rated in MPH
It dictates the a/c tyre limiting speed on the ground (Vtyre)
Low Pressure tyre
Up to 200psi
High Pressure tyre
200-315psi
Two types of braking systems…
Fixed Disk - Floating Calliper
Floating Disk - Fixed Calliper
Both use hydraulic pressure to clamp brake friction pads tightly against a steel disk
Why is the caliper mounted on pins?
To allow for lateral movement known as ‘float’
When do you check break wear indictors?
Only check them with the brakes applied
Carbon Brake advantages/disadvantages
Adv
Lighter
Absorb twice as much heat as steel brakes
Carbon brakes last longer
~30%-175% improvement
Dis-adv
More expensive to fit but longer lifetime
Should ATC be informed if you have hot brakes?
Yes
May put you on a remote stand as you are deemed dangerous as a tyre may explode. So they’d not want you near a terminal building
Anti Skin System
Conroller knows how fast each wheel is spinning
When a wheel slows down, it knows its about to skid
~releases break pressure from that assembly to allow for maximum breaking efficiency
After this, the controller re applies the break break pressure slowly until it gets back to normal
Touchdown Protection
Anti skid usually incorporates touchdown protection
Prevents break pressure being applied
Bounce Protection
If the a/c bounces after touchdown, the system releases break pressure. This allows the wheels to spin up again before the second touchdown
Spin down (t/o or landing)
Spin Up (When coming into contact with runway- locked)
9√P (psi) ==>kts
7.7√P (psi) ==>kts
What is Hydroplanning
Hydroplanning is a result of built up water on the runway
If speed increases, the tyre is lifted off the surface
Results in:
Reduced or no breaking ability
Loss of directional control
Damage to tyres from superheated system
Hydroplane Protection
Protection only on the rear wheels
Prevents the risk of locked rear wheels during touchdown
If gear is selected down and wheel speed is less than ground speed, the systems releases the break pressure on the rear wheel
What happens if the Anti-Skid is inoperative
Landing distance can double
Amber warning caption illuminates if a fault is detected in the anti-skid system
Automatic braking
No pilot input
Solenoid valve is energised after the wheels spin up
This valve feeds hydraulic pressure to the adaptive pressure control valves which adjust the amount of pressure fed to the break units
Automatic braking settings
Setting 1 or MIN= Lowest level of retardation
Setting 3 or MAX= Highest level of retardation
What are the prerequisites before auto braking can be armed?
Auto brake must be ON
Anti skid must be ON
Power levers must be set BELOW a certain value
Hydraulic system must be FUNCTIONAL
Brake pedals must be DEPRESSED
How can auto braking be overriden?
Brakes are applied manually
Throttles set to TOGA power
Rejected takeoff
RTO is a selection available during t/o
RTO provides max braking if following conditions are met:
~Speed greater than 90kts
~Thrust levers idle
~touching brakes will disarm system
Emergency Braking System
All commercial a/c have an alternate hydraulic source for breaking
Emergency Brake Accumulator:
~consists of a break accumulator that provides up to 6 applications of brake if all hydraulic pressure is lost
What are the Emergency Brake limitations?
No Anti Skid
No differential braking
Directional control problems
Usually a maximum of six applications (possible less)
The Parking brake
Allows break pressure to the wheel to be applied & held
Set with parking break lever
Overrides ALL other breaking systems including:
~Anti Skid & Touchdown protection
For this reason, it should NEVER be set in flight
How is the parking break set?
Set when the toe brakes are engaged
When should the parking break not be set?
If your brakes are excessively hot
