Re: B747 technical questions

Date:         03 Aug 97 02:50:16 
From:         k_ish <kenish@ix.netcom..com>
Organization: Netcom
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Michel Gammon wrote:
>
> My guess for the reason for nitrogen instead of air is that nitrogen is
> inert.  During an emergency stop before V1 when maximum braking is used, I
> suspect the internal tire temperatures can get very high (the external
> surface will at least be afforded some air cooling, while the gas in the
> tire will be insulated from external air and thus will not be cooled).
>
> Mike Gammon

In the PBS TV series and book "Twentieth-Century Jet" (about the 777
development program), there is a segment (photo in the book) about test
flights.  One test involved ballasting the aircraft to MTOW,
accelerating to V1, then doing a maximum-performance stop.  IIRC, this
dissipated approximately 1.5 billion foot-pounds into the braking
system.  On the TV segment, the brake disks are glow orange-hot, and the
tires start to burn.  The aircraft then had to remain in place for 5
minutes (simulated crash crew response time) before any attempt to
extinguish the fire was made.  The idea was to demonstrate that the fire
would not spread.

So yes, the brakes can heat the tires to very high temperatures.  The
rims usually contain fuseplugs to deflate the tire in a non-catastrophic
way.

Lastly, in the book "727 Scrapbook" by Len Morgan, there is a chapter on
a Braniff 727 where a dragging brake overheated a tire.  It exploded
after retraction, and blew off the gear doors and a large hole in the
top of the wing.  The aircraft made a safe landing.

Ken Ishiguro