Performance envelope of the SR-71

As my news server doesn't let me post to a.b.p.aviation, this is the
next best place I can think of for this reply. In answer to a question
about pictures of the SR-71 showing a shock wave, several people have
responded saying that the SR-71 is not supersonic at low level. Looking
for confirmation, I found this URL

http://www.wvi.com/~lelandh/exec12.jpg

- a page from "The SR-71 Reconnaissance System Executive Handbook",
written by Bill Majors (Lockheed ADP), which gives the performance
envelope of the SR-71. And yes, it is subsonic to about 20,000 feet.

OK! Where's the picture?

"Alan Dicey" wrote in message
...
As my news server doesn't let me post to a.b.p.aviation, this is the
next best place I can think of for this reply. In answer to a question
about pictures of the SR-71 showing a shock wave, several people have
responded saying that the SR-71 is not supersonic at low level. Looking
for confirmation, I found this URL

http://www.wvi.com/~lelandh/exec12.jpg

- a page from "The SR-71 Reconnaissance System Executive Handbook",
written by Bill Majors (Lockheed ADP), which gives the performance
envelope of the SR-71. And yes, it is subsonic to about 20,000 feet.

begme wrote:
OK! Where's the picture?

Er - I didn't make that as clear as I could have done, did I? I don't
know of a picture that shows the SR-71 and its supersonic shock wave;
but the performance figures indicate that you would need an exceptional
camera to capture it from ground level, or another SR-71 to capture it
from altitude...

On Sat, 19 Jul 2003 15:12:30 +0100, Alan Dicey
wrote:

As my news server doesn't let me post to a.b.p.aviation, this is the
next best place I can think of for this reply. In answer to a question
about pictures of the SR-71 showing a shock wave, several people have
responded saying that the SR-71 is not supersonic at low level. Looking
for confirmation, I found this URL

http://www.wvi.com/~lelandh/exec12.jpg

- a page from "The SR-71 Reconnaissance System Executive Handbook",
written by Bill Majors (Lockheed ADP), which gives the performance
envelope of the SR-71. And yes, it is subsonic to about 20,000 feet.

I hate to tell you this, but 20,000 ft isn't "low level". Low level
is a couple of hundred feet off the deck. I suppose you could stretch
it to 10,000 ft or so, but the SR is still subsonic at that altitude.

Mary

--
Mary Shafer Retired aerospace research engineer

"A MiG at your six is better than no MiG at all."
Anonymous US fighter pilot

Had a conversation with Daryl Greenameyer about the SR and he commented the
Q-limit (max permissible indicated airspeed) was 600 kts (IIRC). That would
make is subsonic at sea level, supersonic @ 20K.

R / John

"Alan Dicey" wrote in message
...
As my news server doesn't let me post to a.b.p.aviation, this is the
next best place I can think of for this reply. In answer to a question
about pictures of the SR-71 showing a shock wave, several people have
responded saying that the SR-71 is not supersonic at low level. Looking
for confirmation, I found this URL

http://www.wvi.com/~lelandh/exec12.jpg

- a page from "The SR-71 Reconnaissance System Executive Handbook",
written by Bill Majors (Lockheed ADP), which gives the performance
envelope of the SR-71. And yes, it is subsonic to about 20,000 feet.

Mary Shafer wrote:
I hate to tell you this, but 20,000 ft isn't "low level". Low level
is a couple of hundred feet off the deck. I suppose you could stretch
it to 10,000 ft or so, but the SR is still subsonic at that altitude.

?????

Mary, given your past association with the Blackbird, I am perplexed
that you choose to castigate my use of the English language rather than
give us the benefit of your experience: the site I gave a link to says
that the information is unclassified, and I had hoped that you could at
least confirm that it was broadly correct. I can only read your
response as telling me that I should have written "/relatively/ low level".

Looking at the graph I linked to should make it clear that my whole
point was that the SR-71 was subsonic at levels low enough to be seen
and photographed from ground level, and indeed all the way up to 20,000
feet or so.

I would say that you can't call it "low flying" until one or more of the
crew, ground observers or wingmen are scared My father-in-law ended
up as a specialist Navigator on Canberra PR9's after a career which
included Vulcans and Phantoms; he reckoned you weren't into "low flying"
until you got down to 50 feet.

To get back to the original question: do you know of any photographs
that show the shock-wave pattern generated by an SR-71? I can't imagine
that any exist, other than of wind-tunnel models, but the original
enquirer (on a.b.p.aviation) thinks so; what might he be thinking of?

Mary Shafer wrote in message . ..
On Sat, 19 Jul 2003 15:12:30 +0100, Alan Dicey
wrote:

As my news server doesn't let me post to a.b.p.aviation, this is the
next best place I can think of for this reply. In answer to a question
about pictures of the SR-71 showing a shock wave, several people have
responded saying that the SR-71 is not supersonic at low level. Looking
for confirmation, I found this URL

http://www.wvi.com/~lelandh/exec12.jpg

- a page from "The SR-71 Reconnaissance System Executive Handbook",
written by Bill Majors (Lockheed ADP), which gives the performance
envelope of the SR-71. And yes, it is subsonic to about 20,000 feet.

I hate to tell you this, but 20,000 ft isn't "low level". Low level
is a couple of hundred feet off the deck. I suppose you could stretch
it to 10,000 ft or so, but the SR is still subsonic at that altitude.

Mary

Is there a physical reason why? Or is it because of rules/regulations?
David.

David McArthur wrote:

Mary Shafer wrote in message . ..
On Sat, 19 Jul 2003 15:12:30 +0100, Alan Dicey
wrote:

snip

- a page from "The SR-71 Reconnaissance System Executive Handbook",
written by Bill Majors (Lockheed ADP), which gives the performance
envelope of the SR-71. And yes, it is subsonic to about 20,000 feet.

I hate to tell you this, but 20,000 ft isn't "low level". Low level
is a couple of hundred feet off the deck. I suppose you could stretch
it to 10,000 ft or so, but the SR is still subsonic at that altitude.

Mary

Is there a physical reason why? Or is it because of rules/regulations?
David.

I believe someone mentioned that it's a Q limit (i.e. physical strength of the airframe), 600? KCAS in this
case.

Guy

Mary Shafer wrote:

OK, a guy at LaRC figured out a way to take Schlieren photos of the
shock field using a modified camera, an airplane, and the sun. He
took a photo of a T-38 at Wallops that ended up in AvLeak.


Go to www.dfrc.nasa.gov and select the technical reports. Search for
Ed Haering. One of his papers is about the two F-18s experiment and
another is about mapping the SR-71 shock field. One or the other
should have the Schlieren. If not, try the press releases. This is
probably from about 1996.


Thank you Mary, your pointers are exactly what I was hoping for.
Searching the Dryden reports server gave me several hits for Ed Haering,
but most of them were to do with sonic boom recording. I did find the
following relevant links, though: -

NASA Factsheet: Schlieren Photography - Ground to Air
http://www.dfrc.nasa.gov/Newsroom/Fa...-033-DFRC.html

Schlieren Photo Gallery Contact Sheet
http://www.dfrc.nasa.gov/Gallery/Pho...TML/index.html

Schlieren EC94-42528-1: Schlieren photograph of T-38 shock waves at Mach
1.1, 13,000 feet
http://www.dfrc.nasa.gov/Gallery/Pho...94-42528-1.jpg

Your confirmation that Schlieren photography was the technique in use
was valuable in itself: I couldn't be sure that NASA hadn't found some
other exotic way of photographing shock waves!

A little more searching lets me find this report on the Langley
server: "Visualization and Image Processing of Aircraft Shock Wave
Structures"

http://techreports.larc.nasa.gov/ltr...sfvip-lmw.html

It contains Schlieren photos of T-38, F-18 and SR-71 shock waves: but,
the SR-71 shock wave photo's do not include the image of the aircraft!