Performance envelope of the SR-71

[Alan Dicey]

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]

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.
>

[Alan Dicey]

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...

[Mary Shafer]

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

[John Carrier]

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.
>

[Alan Dicey]

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?

[David McArthur]

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.

[Guy Alcala]

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

[Alan Dicey]

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/FactSheets/FS-033-DFRC.html

Schlieren Photo Gallery Contact Sheet
http://www.dfrc.nasa.gov/Gallery/Photo/Schlieren/HTML/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/Photo/Schlieren/Small/EC94-42528-1.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/ltrs/dublincore/1997/NASA-97-1psfvip-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!