Path: utzoo!dciem!client2!bgm
From: bgm@client2.dciem.dnd.ca (Bruce Matthews)
Newsgroups: sci.space.shuttle
Subject: Re: shuttle landing sites
Message-ID: <1216@client2.dciem.dnd.ca>
Date: 21 Nov 88 19:16:04 GMT
Article-I.D.: client2.1216
Reply-To: bgm@client2.dciem.dnd.ca (Bruce Matthews)
Organization: D.C.I.E.M., Toronto, Canada
Lines: 33

In article <434@geovision.UUCP> alastair@geovision.UUCP (Alastair Mayer) writes:
>
>As for dumping fuel for emergency landings, the problem can hardly
>be the weight on gear or runway -- after all, the thing has already
>been taxiing around with a full load before it took off!   No, the
>fuel dumping is done for a couple of reasons - to reduce the mass
>that the aircraft brakes will have to slow down (sure, they *can*
>handle a fully loaded 747 at takeoff speed in case of aborted takeoff,
>but it doesn't do the brakes any good), and also to reduce the
>amount of fuel that could be involved in any post-crash fire, if
>the emergency landing ain't too smooth. The former reason is probably
>the stronger reason, reduce the mass to reduce the braking effort
>needed (which in turn reduces the chance of further damage from locked
>brakes, blown tires, etc).

I don't want to wet on your charcoals, but as Steve and I have pointed out
- it IS the weight on the gear.  Saving the brakes is not a factor.  For
the FAA to certify an aircraft it must pass a brake test: the aircraft is
put through a refused take-off (aka aborted take-off) at max take-off 
weight.  The speed at the abort time is V1 (critical engine failure
recognition speed) - any faster and you better decide to fly.  After the
aircraft comes to a full stop, it must sit for 5 minutes without fire
breaking out in the landing gear area.  When this test was done with the
747-400, the carbon brakes glowed red for a number of minutes, but no fire
resulted.  Sure the brakes may be next to useless afterward, but they are
cheaper to replace than entire landing gear assemblies.

The approach speed argument seen earlier is also a secondary factor - but
if you bounce a 747 at higher than max landing weight, the next bounce will
likely put the gear struts through the cabin floor and into the wings as
well. (Yes I have seen a 747 bounced - severely!)

BGM