Re: aborted takeoff and brake damage

Date:         06 Sep 97 02:55:07 
From:         "Richard Isakson" <rwi@whidbey.com>
Organization: WhidbeyNet
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Peter <peter@whistler.ee.uec.ac.jp> wrote in article
<airliners.1997.2019@ohare.Chicago.COM>...
<snip>
> 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

The brakes are designed to absorb the energy of the aircraft and dissipate
that energy off as heat.  On a heavy weight aborted takeoff the brakes can
get red hot and even start a tire fire.  If there is no damage to the
brakes during the abort the airplane could turn around and take off
immediately.  But what happens if you have to abort a second time?  The
brakes can only take so much heat before they break or catch fire and they
haven't dissipated all the heat from the last stop.  Therefore, it's
necessary to give the brake a chance to cool off before the next takeoff.

The ability of the brakes to absorb energy is one of the factors that
limits the airplane's takeoff gross weight.

Rich