Brakes Flashcards
Brake fade
Result of brakes overheating
The brakes will not be able to absorb any further energy
Will fail with pressure still applied to the break pedal
Overheated brakes may judder
Brake drag
Brake is coming on but not coming off correctly
Wrongly adjusted or faulty brake adjuster - may contribute to brake fade
Multi plate brake operation
Consists of interleaved stators and rotors
Brake application compresses the stator disks together and brings them into contact with the rotors
Multi plate brake components and their functions
Rotors - tongues that look onto the wheel
Torque plate - pistons operated by hydraulics, push the sandwich together
Adjuster - makes sure there is enough clearance
Plates are made of
Heavy steel with a special case hardened surface carbon
Why are brake plates case hardened
To prevent thermal shock
In the event of wheel or brake fire - what to use
Dry powder
Liquid may cause the pads to explode
How to judge brake wear
By checking how much the retraction pin protrudes from the brake housing - with the brakes on or applied
Advantages of carbon brakes
Lighter
Absorbs twice as much heat as steel
Less prone to brake fade - can still happen tho
Last longer but more expensive to fit initially
Anti skid systems
Monitors individual wheels - reduces pressure to a specific wheel then re applies pressure - process happens very rapidly
Monitors wheel rotation
Intelligent braking/ bias modulation
Every time the brake applies pressure - will reduce the pressure by a small amount each time
Advantages of an electrical anti skid
Music quicker response rates than mechanical and modulation is matched closer to actual r/y conditions
Easier to adapt the system to different a/c and can be tested prior to use
3 main components of electrical anti skid
Wheel speed/signal gen
Control box to compute wheel sped information
Servo valve to modulate brake pressure
Electronic anti skid operation
Uses a small gen driven by the wheel assembly
Anti skid controller cross references signals from all the wheels - estimates a/c speed based on wheel speed - predicts the slip ratio - at a set value - reduces pressure to that wheel - allows it to spin back up - pressure is re applied at a lower pressure to find the max braking force
Anti skid unit functions
Skid prevention - heart of the system
Locked wheel protection - monitors individual wheels for locking rather than skidding
Touch down protection - stops you l/d with foot on the brakes - applies auto brakes under certain criteria
Hydroplane protection - looking at all the wheels on the set to be locked
Anti skid is deactivated at
20 mph
Either manually or automatically
Touch down bounce protection
If the a/c bounces after the initial touchdown - the system releases any brake pressure allowing the wheel to spin up again before the second touchdown
Locked wheel protection
If the wheel locks because of wet patch or ice - controller will release the pressure to that wheel completely - then re apply
If both the normal and alternate hydraulic system fails - brakes
An accumulator is automatically selected
Torque limiting - brakes
Sensor is provide on each wheel - brake bar - senses torque during braking - prevents you putting too much strain on the l/d gear - pressure will be released - more of a problem with carbon brakes
Auto-brakes will not work when
A fault occurs - automatically disconnect
Auto brakes are not available when using the alternate braking system or s/by
Auto brakes in the armed posn takes indications from
Weight on wheels
Bogie orientation
A signal from 2 separate wheels
RTO mode
Rejected t/o mode
Max brake pressure will be applied when all thrust levers are closed at ground speeds above 85kts - on all the wheels
Pre flight check - select RTO
When will the autobrake move to the disarm posn
If a fault occurs
Operation of foot brakes
Advancing of any foot brakes
Moving the speed brake lever down after speed brakes have been deployed on the ground
Normally disarm by a non handling pilot/ ground engineer as the a/c slows to 20kts
Slip ratio
Main wheels spinning faster than the nose wheel - if this occurs - put brake on
