From: shafer@rigel.dfrf.nasa.gov (Mary Shafer)
Newsgroups: sci.military
Subject: Re: SR-71 top speed estimatates
Date: 14 Apr 92 00:47:02 GMT
Organization: AT&T


From shafer@rigel.dfrf.nasa.gov (Mary Shafer)

On Sat, 11 Apr 1992 00:18:27 GMT, prm@ecn.purdue.edu (Phil Moyer) said:


Phil> From prm@ecn.purdue.edu (Phil Moyer)


>From kdrolt@athena.mit.edu (Kenneth D Rolt)

>... The
>question is, if the trip distance was much shorter, say 200-300 miles, instead
>of 2000 miles, how fast could they have gone?  And finally, what is the true
>top speed of the aircraft?

Phil> The "SR-71 Supersonic/Hypersonic Research Facility Researchers Handbook",
Phil> published by NASA, has (on page 11) a Dynamic Pressure Range listed.  Using
Phil> that set of numbers (325-847 lbs/sq.ft), it is possible to back-calculate
Phil> a theoretical equivalent velocity.  At 85,000 feet, that velocity is
Phil> 3,410 mph.  Using the speed of sound at 85,000 feet (663.6 mph), that equates
Phil> to Mach 5.14.  No, that's not a typo, that's Mach five-point-one-four.

That can't be right.  The maximum Mach at 85,000 ft is 3.3 and we routinely
fly at 3.2 (I've just trotted down the hall and checked with one of the
backseatters.  She and I looked in the Dash 1.)

The limits are not as simple as you've set forth.  If you look at the
flight envelope you'll see that there are a number of limits at
different places.  For example 847 psi may be the limit at lower
altitudes and Mach 3.3 may be the limit at higher altitudes.  You
cannot assume that the highest q-bar is at the corner of the
envelope--it almost invariably isn't.

In this case the Mach number sets the limit because of the impingement
of the shock on the vehicle. 

(Q-bar is usually in psi, not psf--are you sure about this?)

Phil> [Thanks to Larry Smith for these calculations.  -prm]

I'm not sure you should thank him--he's led you badly astray.

>I haven't checked Jane's so I don't know if they
>have an estimate.  Also, NASA now has at least two SR-71 which will probably
>be painted NASA white, thus making the plane the Whitebird.

Phil> NASA has three SR-71s.  They are:

Phil> 	Serial Number	Article Number	Model
Phil> 	------------	-------------	-----
Phil> 	64-17956	2007		SR-71B
Phil> 	64-17971	2022		SR-71A
Phil> 	64-17980	2031		SR-71A

Actually these aircraft are N831NA, N833NA, and N844NA, respectively,
usually known as 831, 833, and 844.  NASA gives its planes civil
registries and Dryden has been assigned all of the N8xxNA block.

Phil> They will *not* be painted white. :-)  At least, not to my knowledge.
Phil> Perhaps Mary Shafer can confirm this.

They have had the NASA worm, in red, and the number, in white, added
to the verticals.  (We stopped using the yellow band years ago and it
has gradually attrited off all our planes due to regular maintainence.)  
Perhaps this misled the original poster.

Phil> In addition to the three NASA birds, the Air Force has three in flying
Phil> storage at Lockheed's Plant 42 in Palmdale, CA.  This makes a total of
Phil> six operational Blackbirds.

The latest word here at Dryden is that we're getting the other 3 as
well, so that all the possibly-flyable aircraft will be here.  The
intent is not for us to fly them, but for them to be stored here.
Some of us peons think it's so the Air Force doesn't have to maintain
a separate facility with guards, etc.  We've already got that stuff.

Mary Shafer  DoD #0362 KotFR NASA Dryden Flight Research Facility, Edwards, CA
shafer@rigel.dfrf.nasa.gov                    Of course I don't speak for NASA
 "There's no kill like a guns kill." LCDR "Hoser" Satrapa, gunnery instructor
                       "A kill is a kill."  Anonymous