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From: shafer@ferhino.dfrc.nasa.gov (Mary Shafer)
Subject: Re: Blackbird fuel
Date: Wed, 20 Mar 1996 21:11:36 GMT

On Tue, 19 Mar 1996 22:24:45 GMT, wb8foz@netcom.com (David Lesher) said:

D> I seem to recall reading that SR-71's used a thick gummy fuel that
D> was in effect, preheated by cooling the skin.

This is kind of an exaggeration.  JP-7 is about the weight of 3-in-1
oil, which isn't exactly thick.  It's not gummy, either; I've run my
hand along the keel and collected some and it's just oily.  It wipes
right off.

D> But a friend who observed them being prep'ed many times at
D> {somewhere damn hot}, told me he recalled an exotic COOLING system
D> on the fuel hoses connected to it; one that in itself was a
D> constant hassle to keep working. He described a coaxial connector
D> with JP-whatever in the middle & refrig. surrounding it.

He's only a little confused.  What he saw was, I think, TEB.  Ask him
if everyone was in fancy silver fire suits.  If so, it was TEB.

TEB is the "igniter" for JP-7.  You can't get JP-7 to burn without it
in the SR-71, as the ignition of JP-7 takes a higher temperature than
is conveniently produced otherwise.  You drop in a shot of TEB, which
bursts into very hot flames the minute it has any oxygen, and this
ignites the JP-7.  Once ignited, the JP-7 keeps burning.  The plane
has twelve shots of TEB (either total or per engine, I forget), using
one shot for each engine start and one for each burner light.

I watched them TEBbing the plane once, keeping well back and being
careful to not stand between the big green firetruck and the crew.
They had a very, very tiny leak between the TEB nozzle and the
aircraft fitting and were getting a drop of TEB released about every
20 seconds.  These drops would be on fire as they fell, but they (sort
of like most meteorites) burned completely before they reached the
ground.  It was really pretty, but I was glad it wasn't me in the
silver fire suit.

D> So what is accurate? How much of it is light ends vs #6 bunker
D> grade?

Think 3-in-1 oil or sewing machine oil.  Light, clear, but definitely
more like oil than like gas.  Then add a non-hydrocarbon that bursts
into flame on contact with oxygen and lights off the oil.

D> [He also expressed astonishment that Dryden could AFFORD to keep
D> such going.. "Do you have ANY idea how much money those things
D> sucked?"  were his approx. words...]

We only have two flying (right now we only have two, period) and it's
a lot cheaper for us to operate them than it was for the Air Force.
The Air Force had to include a lot more in the price of operating more
planes from dedicated bases.  The base and its management (including
everything from the housing and roads onward), the medical facilities,
flight surgeons, chase planes, the SPs, the crews and associated
management, squadron administration, wing administration, base
administration, command administration, stores, payroll, financial
management, chaplains, MWR, barbers, open messes, clubs, and on and
on.  There's a tremendous infrastructure required to fly any airplane,
from small single-engine general aviation aircraft on up to SR-71s.
We didn't add more than one or two civil service staff, though we did
add at least two contracts (for the engines, with P&W, and the
airframe, with Lockheed) and the Air Force provides the pressure suit
support.  We already have all the other pieces here and adding another
couple of aircraft didn't really increase our costs at all, although
our workload did increase in some areas.  The spares came with the
planes, too.

It's really two different sides of economy of scale.  We already fly a
lot of aircraft, so we had all that we need for that in place, which
is the classic economy of scale.  Then we only took on two more
aircraft, which is sort of the reverse of economy of scale, if you see
what I mean.



--
Mary Shafer               NASA Dryden Flight Research Center, Edwards, CA
SR-71 Flying Qualities Lead Engineer     Of course I don't speak for NASA 
shafer@ferhino.dfrc.nasa.gov                               DoD #362 KotFR   
URL http://www.dfrc.nasa.gov/People/Shafer/mary.html



Newsgroups: rec.aviation.military
From: shafer@ferhino.dfrc.nasa.gov (Mary Shafer)
Subject: Re: Just how fast and high can the SR-71 go?
Date: Wed, 20 Mar 1996 21:35:18 GMT

On Wed, 20 Mar 96 00:31:05 GMT, keenan@inforamp.net (Martin/Jennifer Keenan) said:

M> According to Mary, they (NASA) stick to Mach 3.2.  This was the
M> normal operating limit before - going to Mach 3.3 required the
M> Squadron Commanders OK, according to the flight manual.

Right, sort of.  Those numbers are for a standard day.  On a cold day,
the Mach can be a little higher for the same inlet temperatures.
We've flown a number of flights at 3.22 or 3.23, for example.

On a hot day, of course, it goes the other way.

I mentioned that the service ceiling is 85,000 ft, but I should also
tell you that the plane has been to 90,000 ft.  However, the current
envelope is 85K, not 90K.  I suspect that the plane wasn't very
satisfactory at 90K; pilots do like some response to their control
inputs, after all.

--
Mary Shafer               NASA Dryden Flight Research Center, Edwards, CA
SR-71 Flying Qualities Lead Engineer     Of course I don't speak for NASA 
shafer@ferhino.dfrc.nasa.gov                               DoD #362 KotFR   
URL http://www.dfrc.nasa.gov/People/Shafer/mary.html

From: Mary Shafer <shafer@reseng.dfrc.nasa.gov>
Newsgroups: rec.aviation.military
Subject: Re: Question for Mary Shafer about SR-71.
Date: 15 Apr 1998 12:32:43 -0700

sferrin@xmission.com (D. Scott Ferrin) writes:

> I have a some questions.  The *maximum* altitude and airspeed for the
> SR-71 is generally given as "Mach 3.2 and 85,000 ft".   How is it that
> the SR-71 was designed to operate for extended periods of time at
> those figures but not the *slightest* bit more could be gotten out of
> it?  I think part of the reason everybody has a problem believing that
> those figures are absolutes is that because it does it so routinely.
> Most equipment, whatever it may be, does not operate in the "redline".
> By stating these figures are both the maximum and operational figures
> it's saying that they redline these valuable aircraft routinely.  Most
> mechanical devices have a "comfort zone"  where they can be operated
> at for extended periods of time with fairly predictable behavior.  For
> the SR-71 this happens to be 3.2 and 85k.  There is generally some
> room between "comfort" and "disaster".  THAT'S what we'd all like to
> know- how much is there?  I know that on the SR-71s "last" flight
> where it set records it hit 2,242 mph for several minutes which is
> about Mach 3.4.

Of course they could fly a bit higher and a bit faster, but not much
and not for long.  There is a difference between cruise and dash, not
to mention the variablity of the atmosphere, that makes this possible.
After all, I've repeated mentioned that we cruise at about 3.23 Mach
and go somewhat above 85,000'.

I was not involved in any way in the specification, design,
construction, acceptance, or USAF operation of the SR-71.  Everything
I know about it comes from reading books available openly, from our
operation of the aircraft, and from general knowledge gleaned
throughout about 30 years of working in flight test and flight
research.  Because of this, much of what I have to say is speculation
and shouldn't be regarded as inside knowledge.

The SR-71 is what's known as a point design aircraft.  Everything
about it was designed to work perfectly for the length of a flight at
the design flight condition.  No more, no less.  The aircraft was
built and the hardware specified so that the redline was just beyond
the design point.  The only compromises were those necessary to get
the plane from the end of the runway to the design point.  Kelly
Johnson and Ben Rich both said this repeatedly.  I've heard them both
do it in person.

When you're building a special-purpose airplane, to be operated under
very controlled conditions by very skilled pilots, it's possible to
make the pad between "OK" and "oh-oh" pretty small.  The U-2 is,
according to numerous publications, operated much closer to its limits
than the SR-71 is.  I've read articles that claim that the airspeed
envelope is less than 5 KIAS wide up at cruise altitude for this
airplane.  Too slow and you stall, too fast and you rip the plane
apart.  Again, I don't have any more information about this than what
I've read in the open literature, but this seems to be pretty widely
accepted.

This is in marked distinction to "regular" aircraft.  Airplanes like
the F-15 and F-18 have more generous envelopes and can be flown by
pilots with a wider range of skills.  They're designed that way on
purpose.  It would be foolish to make such aircraft as finicky as the
special-purpose aircraft like the SR-71 and U-2.  If you read Richard
Graham's book about being an SR-71 pilot and compare it to the
accounts of pilots like Duke Cunningham, you'll see a real difference
in the entire approach to the operation of the different types of
aircraft.  The SR-71 operation was very driven by the flight
characteristics of the airplane, whereas combat operations are very
driven by weapons and ordnance characteristics and combat tactics.
That's exactly as it should be--the last thing a fighter pilot should
be doing in combat is fretting about a couple of degrees difference in
something like compressor inlet temperature.

There's one last point I should mention.  Several of the books I've
read about the SR-71 imply that the original design point was Mach 3.0
at 80,000'.  If this is true, then I would speculate that operation at
a higher Mach and altitude would just indicate that the USAF and
Lockheed discovered that the airplane performed better than they
thought it would, so that they were further below the redline than
they intended to be.  Rather than keep this excess capability as a
reserve, they would have decided, if this is true, to use as much of
the extra capability as they safely could in normal operation.  If
that's the case, it's not surprising that there's very little pad.
Considering the importance of the data the SR-71 brought back, and the
risks inherent in sending it out to get this data, it's not exactly
surprising to think that they'd use every bit of capability the
airplane has.  I certainly would in their place.

--
Mary Shafer               NASA Dryden Flight Research Center, Edwards, CA
SR-71 Flying Qualities Lead Engineer     Of course I don't speak for NASA
shafer@reseng.dfrc.nasa.gov                               DoD #362 KotFR
URL http://www.dfrc.nasa.gov/People/Shafer/mary.html
For personal messages, please use shafer@ursa-major.spdcc.com




From: Al Bowers <bowers@orville.dfrc.nasa.gov>
Newsgroups: rec.aviation.military
Subject: Re: SR-71 / YF-12
Date: 21 Dec 1999 10:59:37 -0800

[apologies, lost attributions]

>>> it would encounter at Mach 3, so they left it out and left the
>>> expanding of the Blackbird's titanium skin when it encountered
>>> those Mach 3 speeds to seal the leak.

>> Titanium gets smaller when it gets hot.  The charectoristic that
>> makes titanium desireable for high temperature use is its crystal
>> structure shrinking at temperature.

> Sigh. Then please explain why the aircraft grows in length at speed.

Titanium has a coefficient of thermal expansion of 5.2 x 10^-6 (a
positive number, so it expands with increasing temp).

The SR-71 lengthens by about 12 inches at it's design cruise Mach
number of 3.0.

The only aircraft that grows more in length due to aerodynamic heating
is the Concorde (aluminum structure, coefficient of thermal expansion
is 22 x 10^-6), which at the end of it's Mach 2.0 heat cycle, is about
18 inches longer than when it took-off.

Al Bowers

--
Al Bowers    Aerodynamics    NASA Dryden Flight Research Center
"...tactics always degrade strategy..."  -Frank Bethwaite

 



































































































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