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From: deichman@cod.nosc.mil (Shane D. Deichman)
Newsgroups: sci.military
Subject: Re: SR-71 Blackbird question
Message-ID: <1990Sep29.155328.7880@cbnews.att.com>
Date: 29 Sep 90 15:53:28 GMT
References: <1990Sep27.031756.7889@cbnews.att.com>
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From: deichman@cod.nosc.mil (Shane D. Deichman)

>From: bruce@saturn.cs.swin.oz.au (Bruce Donaldson)
>
>I once heard a story that the Blackbird could literally undergo
>a "burn up on re-entry" type accident. At first I thought this extremely
>far fetched, but upon hearing of the plane's fantastic altitude 
>(80,000 ft plus ?) and speed (literally faster than a lee-enfield Mk4 bullet) 
>I began to wonder. 
>
>A shallow dive could presuamably build up sufficient energy so that a rapid
>climb could convert this to additional height. I know that you
>don't have to reach vacuum to  "burn up on re-entry" so the plane needn't be
>space-capable. 
>
>Any thoughts or facts ?
>

I seem to recall hearing something about the properties of the "skin"
of the Blackbird.  If memory serves correct, the plane was covered 
with a polymeric composite which, due to the friction of high speed
flight in a resistive medium (even at high altitude), would essentially
melt -- i.e., become amorphous -- and recongeal as it cooled.

The interesting thing about polymers is that they contract when heated
(since the long molecular chains get kinked up with the added kinetic
energy), so one would suspect that the Blackbird, upon close examin-
ation, would appear almost wrinkled.  Of course, I've never been
close enough to see this for myself....

As for the question of "burn up on re-entry", I suppose it's possible --
if they went into a steep high-speed dive.  However, it is up to the 
coating to dissipate as much of this energy as possible.


  |\/\/\/\/|
  |        |
  |        |
  |   (o)(o)
  c        _)
  |  ,____/
  |     /
 /_______\           "I'm outta here, man!"

 -shane d deichman