Accumulator braking
 

If you only have the accumulators for braking,no anti-skid,how long do you apply brake pressure for before releasing?

Preferably until you stop because you're limited by brake applications and not duration of braking.

Typically you have a maximum of seven applications at about 1000psi so do you hold one application or release so that you don't shred the tyres?

How would you stop a car without ABS?

Cars generally do not operate on limited lengths of road.I was just interested in the technique of braking a heavy aircraft with no anti-skid and limited brake pressure. Can you lock a wheel at 1000psi ? Has anybody on here tried it for real rather than the sim?

I only know about the A300.
Recommendation is to not exceed 1000 psi brake pressure without anti skid. A fully charged accumulator will be at 3000 psi. This will give about 6 brake applications before the stored pressure is dissipated. Best practice is to apply brakes gently and have another crew member call the indicated pressure so you can adjust foot pressure accordingly.
Yes you can lock a wheel with 1000 psi if the surface is slippery.
Yes I have been part of a crew that did this for real with a dual hydraulic failure, and we did not flat or burst any tyres.
Me in middle seat.

Dixi thank you for the reply. Was the technique used ,squeeze the brakes until 1000psi is achieved then release or hold if for a few seconds then release?

Accumulator braking only with critical length runway is a challenge that would send me to a more suitable airport.

If you have such a failure, you are probably not going to head for a limiting runway, so why not just brake at a normal rate?

(I think I crossed posting with Autoflight - same answer really)

Tubby,
Technique is to apply the brakes once only if possible and hold the 1000 psi until low speed and then reduce pressure gently until stopped. Then set the parking brake, shut down and get towed off the runway.

I heard a story of a Canberra that landed at Akrotiri with hydraulic failure. The one shot emergency brake was used with success. The tower then asked if he could taxi off the runway as there were some Victors waiting to take off. The pilot released the brake and then rolled off the end of the runway having neither brakes or steering. Result: runway closed.

Interesting,once again Airbus provides info Boeing does not..thanks for info.


Doop:E

Tubster, can you read tech manuals?:ok:

Somewhat off topic but related:- Citroens with hydro-pneumatic brakes, including the magnificent DS and CX designs, had just such .a system (Also licensed to RR for the Shadow and Spirit .
For the tech . minded, Citroen used a belt-driven multi-cylinder Swash-plate pump which charged an accumulator , being a sphere with a diaphragm dividing it. the back of the diaphragm was nitrogen-pressurised. A priority- valve sequentially isolated the Suspension, Steering assistance and finally the brakes.
With a good accumulator , a half-dozen applications could be performed.

This presupposes you ignored the christmas-tree of red panel "STOP" lights.

It was possible to "ease" the brakes and thus extend the cycles, but frightening in 2 tons of Rolls, the parking-brake of which was somewhat marginal!

A steady pressure to standstill is the technique of choice and i guess the aircraft system is the same.

Of course, if you empty the accumulator through repeated applications of the brakes, you won't be able to set the parking brake...