Blackbird

[steveb at newkla.kla.com]

WRT SR-71 and it's fuel ...

It turns out that there aren't deliberate holes in the SR-71's fuel tanks 
per se, the designers simply decided to use the wing surfaces as the con-
tainers for the fuel rather than having separate tanks.  Since the mater-
ials expand under temperature they were actually designed to slide relative 
to each other as the individual pieces expanded.  This allowed expansion of 
the pieces without changing the shape of the airfoil.  The reason the tanks 
leaked is that fuel could seep between the sliding joints when the surfaces 
were cold.  

The fuel for the SR-71 is a form of kerosene, not any kind of gelatinous 
material.  The interesting feature of the fuel (JP-8) is that it is actually 
very difficult to get it to burn!  I've seen demonstrations where a lit 
match was tossed into a container of JP-8; the match was actually extin-
guished by the fuel and vapors.  To start the engine or light the after-
burners it is necessary to inject tri-ethyl borane (TEB) into the engine.
I think the TEB is a hypergolic material, which establishes a high enough 
temperature to support burning of the JP-8.  It is actually interesting to 
watch an SR-71 motor start because the TEB injection causes a green flash 
in the engine.

I guess that jet engines employ fuel injection, probably not DIY though :)
but to bring the subject back toward automotive powerplants ... I went up 
to Beale AFB for an open-house when the SR's were active up there.  As I 
was walking amongst the jets on the tarmac I heard a sweet-sounding V-8 
on cam.  I had noticed that there was a group of '50's american cars up 
ahead so I thought it was one of them.  It turned out that I was wrong ...
to spin the engines of the SR to the point where they could start they had
built an APU that was built from a pair of Buick small-blocks, coupled 
together through turbo-hydramatic trannies, which would then connect to 
the shaft that spins the turbine/compressor shaft of the jet engine.  They 
had really tricked the motors with all kinds of chrome and performance 
goodies.  

Ah, to get paid for doing your hobby ... :-)

I hope that this slightly off-topic discussion doesn't bother too many of 
you, but you touched on one of my favorite subjects ... betcha couldn't tell!

Steve Buchholz
s_buchho at kla.com
San Jose, CA (USA)