Re: aborted takeoff and brake damage

Date:         11 Sep 97 03:35:30 
From:         khowie8@gte.net (Keith Howie)
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On 08 Sep 97 02:03:40 , Chris Dahler <dahler@iglobal.net> wrote:

>> 1: what exactly needs to cool down after such a heavy brake application?
>> Is it the hydraulic fluid or the brake discs and pads themselves? I dont
>> understand why hot brake surfaces should work less effectively than cold
>> ones, unless they melt or something
>
>You should see some of the video footage of Boeing doing aborted takeoff
>tests on heavy aircraft for the certification process.  The brakes glow
>red hot.  It isn't the hydraulic fluid, it is the brake surfaces that
>get so hot.
[remainder snipped]

Chris may be referring to the footage of the "refused takeoff" test
conducted during the 777 certification program. I believe this is
contained in the PBS documentary "21st Century Jet". This test is
arguably the most severe in any certification program. For the 777,
the test plane was loaded to its MTOW, then accelerated to V1, the
last point where a takeoff can be aborted. The takeoff WAS aborted,
and the airplane had to be brought to a stop using only the brakes
(i.e., no thrust reversers) within a specified distance (I forget the
exact length). To top it off, the aircraft was then required to sit on
the runway unattended for several minutes to simulate the time it
would typically take to get fire equipment to the plane.

The film footage is spectacular. As Chris says, the brakes are glowing
red from the friction. The tires are all blown out, and God only knows
what other damage resulted. The important thing, however, was that the
damage was contained, nobody was injured, and the aircraft could be
refurbished. Keep in mind that this sort of thing is rare enough that
it is conceivable that it will never occur during the entire service
life of the entire 777 fleet.

Keith