Brake energy a320

[Speedwinner]

Hello!

Ich had recently a discussion with a colleague. So scenario was a ultra light a319 to land with flaps 3 and autobrake low. The discussion topic was: I took the last exit to keep the temperatures down and the colleague said it did not matter where to exit because the brakes take the same energy. The only difference would be the drag and the wind at a longer rollout. So can somebody help me? I think that he says the brakes are ideal and doesn't take into account how they built.

Thanks!

Sw

[dixi188]

It does not have to be an Airbus.

In any aircraft, braking gently will result in cooler brakes since some of the retarding will be done by drag and also some of the heat in the brakes will be dissipated to the air.

On a very light Airbus you might end up with quite warm brakes if you have a long taxi due to many brake applications to stop the speed getting too high.

As an experiment some years ago when landing at CPH on 04L in an A300, I suggested to the training captain that we see how much retardation there would be without using the brakes until later in the roll out. We were a cargo flight at medium weight. So after about 10000 ft of runway, with reverse idle only, we were doing 15kts and turned off without ever having used the brakes.

[Sidestick_n_Rudder]

As Dixi said - the less braking force you apply, or the later you apply the brakes (at lower speed), the less of the total energy is dissipated by brakes and more by aerodynamic forces and reverse thrust.

I did the same experiment as Dixi in A320. With medium weight, idle reverse and some headwind it took 2500-2700 meters to decelerate without touching the brakes.

Having said that, according to Airbus, there's no benefit of keeping the carbon brakes cool (except for short turnaround considerations). Carbon brakes wear does not depend on brake energy absorbed, but primarily on number of applications. Also, they actually wear more at low and moderate temperatures (100-250deg) than at higher temperatures! Only when you exceed ~500degs, the wear increases again due to oxidation.

Have a look at the following video
https://m.youtube.com/watch?list=PLF27ED66B4E69AE8B&v=SG4Aw5BujEU

[jaja]

As Dixi said - the less braking force you apply, or the later you apply the brakes (at lower speed), the less of the total energy is dissipated by brakes and more by aerodynamic forces and reverse thrust.

I did the same experiment as Dixi in A320. With medium weight, idle reverse and some headwind it took 2500-2700 meters to decelerate without touching the brakes.

Having said that, according to Airbus, there's no benefit of keeping the carbon brakes cool (except for short turnaround considerations). Carbon brakes wear does not depend on brake energy absorbed, but primarily on number of applications. Also, they actually wear more at low and moderate temperatures (100-250deg) than at higher temperatures! Only when you exceed ~500degs, the wear increases again due to oxidation.

Have a look at the following video
https://m.youtube.com/watch?list=PLF27ED66B4E69AE8B&v=SG4Aw5BujEU

Brake wear and oxidation is two very different things :

Brake wear is dependant on temperature and number of applications :

The optimum temperature is dependent on which manufacture you have installed (A32x have 3 different) so not just one optimum temperature. No so much you can do to have the brakes at optimum temperature, except using brake fans to control temperature, and use correct flap/reverse/autobrake setting.

But number of applications you as a pilot can do a lot to reduce. Airbus informs that 75 % of brake wear happens during taxi !! Use the 10/30 kts technique.

Oxidation is not wear, but degration of material. The two main causes are repeated high temperatures (> 500 ' C) (thermal oxidation) and runway deicer fluids (chemical oxidation). These two combined accellerate oxidation a lot.

Airbus has quite some imformative documents about the subject.

[vilas]

Also it is recommended to use brake fan when possible after five minutes for thermal equalisation to avoid oxidation of hot spots.

[FlightDetent]

Vilas, is the meaning:
Do not use brake fans for the first five minutes, in order to allow for thermal stabilisation, and thus prevent the oxidation of thermal hot spots?

The exact wording of your sentece may give an opposite impression of brake fans use to some readers, I am afraid.

[vilas]

Vilas, is the meaning:
Do not use brake fans for the first five minutes, in order to allow for thermal stabilisation, and thus prevent the oxidation of thermal hot spots?

The exact wording of your sentece may give an opposite impression of brake fans use to some readers, I am afraid.
Yes. After clearing the runway wait 5 minuites before switching on brake fan.

[dixi188]

What about if you have "Hot brakes".
Do you still wait 5 mins. before turning the fans on?

Some years back one of our A300s had a "Hot brake" warning while taxiing out at Edinburgh due to a dragging brake. The FE turned the fans on and the brake unit then caught fire.
Fortunately they were outside the fire station at the time and things were dealt with very quickly.

[Cough]

'Hot brake' warning occurs at 300C, which is way short of roasting hot! I seem to remember you turn the fans on after 5 min, or straight away if you are going to exceed 500C..

I suggest your 'hot brake' dixi may have been somewhat hotter than 500C!

[Gryphon]

So scenario was a ultra light a319 to land with flaps 3 and autobrake low. The discussion topic was: I took the last exit to keep the temperatures down and the colleague said it did not matter where to exit because the brakes take the same energy

If you are using autobrake...it is not about what exit you take but when you disconnect the auto brake. :ugh: