Re: Braking

Date:         04 Jun 97 01:45:43 
From:         Tony Maddern <tmaddern@cse.unsw.edu.au>
Organization: University of New South Wales
References:   1 2 3 4
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S. Buining wrote:
>
> Matthew Willshee wrote:
> >snip

> One bit I found especially interesting was a part of the flight test
> programme that involved braking from V1 (I think) to a standstill
> using wheel brakes with the engines at full power.There was a minimum
> time limit that the plane then had to stand (the brakes glowing red
> hot) without the undercarriage catching fire.
>
> snip< Due to the temperature rise, the tires will expand (due to
> internal pressure increase) and if the pressure gets to high, a
> pressure fuse will blow, letting the tire run empty. This is to
> prevent a tire burst (which can have pretty nasty consequences).

Some interesting mis-info here. The brake test is done with a rejected
take-off from V1 but the engines are reduced to idle thrust during the
abort. The tyres must remain inflated for a certain period of time after
the aircraft stops. With the engines at max thrust and max braking you
would never stop the aircraft in the runway distance available with the
tyres still inflated.

The brake fuse is a fusible plug in the wheel rim. When it reaches a
certain temperature the plug melts creating a hole in the rim which
lets  the air out of the tyre. Fully automatic and very simple and
reliable. No pilot input is required.

Wheel overheats are dangerous because the rim fails under the tyre
pressure and explodes throwing shrapnel outwards along the line of the
axles. Never approach an overheated wheel from the side!