Carbon Brakes

[LEM]

Anybody can explain exactly why carbon brakes live longer if stressed harder upon each landing?

Thankyou

[Techman]

If you compare carbon brakes to steel brakes then for any given size carbon brakes can absorbe more energy than steel brakes.

Wear on steel brakes are directly related to the amount of energy absorbed. They also tend to fade with high temperatures.

Wear on carbon brakes are related to number of applications and not to energy absorbed. High temperatures also reduces wear.

So one firm application of carbon brakes during landing will reduce wear.

[used2flyboeing]

The Fokker F50 & Boeing 777 has a taxi-brake inhibit - that applies only a couple brake stacks while taxi-ing to inhibit wear -- IE it applies brakes on only a couple wheels - as opposed to all - IE to reduce the carbon/# of times applied theory- which Ive heard recently is bull-shiit.. You can buy kick-asss carbon brakes for your car now at NAPA & Performance Friction - outta California - & yes they work well they DO NOT FADE ! I put them on application were the brakes were marginal from the factory - like a Jeep Grand Cherokee or Ford Excplorer - Jag etc..

[LEM]

The Fokker F50 & Boeing 777 has a taxi-brake inhibit - that applies only a couple brake stacks while taxi-ing to inhibit wear -- IE it applies brakes on only a couple wheels - as opposed to all

Very interesting, Used2, didn't know that.
Can you explain how the system knows he's taxiing?

High temperatures also reduces wear
That's the question: how come?

[fruitloop]

Quote'Wear on carbon brakes are related to number of applications and not to energy absorbed. High temperatures also reduces wear.
I have also heard the term "gassing"above 700 degrees.My understanding of the term is that it means fade (I could be wrong)

[B73567AMT]

B777

Taxi Brake Release
During each taxi brake application, the antiskid system releases the brakes of one axle pair of each main landing gear (if wheel speeds are less than 45 knots). The system sequences through the axle pairs at each brake application, thereby reducing the number of brake applications by each brake. This extends service life and reduces brake sensitivity during taxi.
All active brakes are applied for a heavy brake application, landing rollout, RTO, or when setting the parking brake.
The taxi brake release system operates only with the normal brake hydraulic system.

[Golden Rivet]

This site has some useful info -

http://www.hydroaire.com/downloads/BrakeSavings.pdf

gr

[used2flyboeing]

Its all software - on modern airplanes many computers "know" what mode the aircraft - IE how does the flight lock computer "know" - how does the pressurization computer "know" - IE they infer it from a combination of variables such as squat switchs, prox switches ( PSEU stuff ) - altitude, throttle lever position, wheel speed etc.. Working out the failure effects is even more problematic - I saw a 757 RAT deploy at Atlanta while 50 aircrafts were qued up waiting for microburst storm cells to clear - many aircrafts had one or both engines shut down - the advancing jets ahead of the 757 with engines shut down apparently generated pitot pressure giving the summation of enviromental effects that indicated to the RAT control logic to deloy - IE airspeed, both engines shut down, the air-gnd logic was on the power bus affected by the shutdown engine - same has been the experiance for flight lock computers =- particularly since they are dispatch critical - you cannot have any screwy logic issues with flight locks ..But to answer your question - there is some logic that infers taxi .. Dunlop, ABSC and Boeing have patents on the taxi-brake inhibit - you can look them up & read about the issues on www.delphion.com -