Refuting blackbird folklore

In article ,
"Brian" wrote:

"robert arndt" wrote in message
om...
Same here. I live in northern California so I have heard all the stuff
coming from Beale AFB and the Mach 3.0-3.5 range seems to be the
truth; however, the airframe of the SR-71 is stressed for Mach 4.0
flight. Maybe like the Foxbat this was for emergency only with
resulting damage to the engines and a/c. But I see little need for
such speed given the Blackbird's height invunerability.


What height invulnerability? It worked in the 60's but in todays
environment, there are quite a few missiles that could reach out and touch
the SR-71.

Well, there's "reach," then there's "reach with a decent chance of
hitting it."

The problem is that the few missiles with the height (80,000 feet plus)
didn't have enough targeting capability to hit the Blackbird at that
height, especially in a stern chase. The best they could do would be to
loft one up and try to get in the way.

The newer ones, like the "big" SA-20, might be able to do it, but it
would still be a fairly tough targeting solution - you'd need to loft
one up before the SR-71 was in range, then acquire it while in midair.

--
cirby at cfl.rr.com

Remember: Objects in rearview mirror may be hallucinations.
Slam on brakes accordingly.

Chad Irby wrote:

In article ,
"Brian" wrote:

"robert arndt" wrote in message
om...
Same here. I live in northern California so I have heard all the stuff
coming from Beale AFB and the Mach 3.0-3.5 range seems to be the
truth; however, the airframe of the SR-71 is stressed for Mach 4.0
flight. Maybe like the Foxbat this was for emergency only with
resulting damage to the engines and a/c. But I see little need for
such speed given the Blackbird's height invunerability.


What height invulnerability? It worked in the 60's but in todays
environment, there are quite a few missiles that could reach out and touch
the SR-71.

Well, there's "reach," then there's "reach with a decent chance of
hitting it."

The problem is that the few missiles with the height (80,000 feet plus)
didn't have enough targeting capability to hit the Blackbird at that
height, especially in a stern chase. The best they could do would be to
loft one up and try to get in the way.

The newer ones, like the "big" SA-20, might be able to do it, but it
would still be a fairly tough targeting solution - you'd need to loft
one up before the SR-71 was in range, then acquire it while in midair.

at which point in time, couldn't the 71 see it coming, and maneuver
to make the geometry as bad as for the others?

redc1c4,
curious ground pounder
--
"Enlisted men are stupid, but extremely cunning and sly, and bear
considerable watching."

Army Officer's Guide

In article ,
(frank wight) wrote:

There was a time when I thought that
the blackbird could secretly hit 5 on the
mach meter--but isn't there solid science
agains this? Such as:

I don't think the engines have the ability
to rev up to such a speed. Maybe the jet fuel
itself cannot produce sufficent BTU's (thrust)
to propel it that fast, maybe the fuel lines
are too small to exceed Mach 3.3

Perhaps the real inhibitor is the lack of
enough combustible oxygen to feed the engines
to shatter established speed records.

I know that the outer metal shell of the
jet couldn't sustain the high atmospheric
friction.

Am I right about all this, or is there OTHER
things to consider?

Besides things like exceeding the allowed inlet temp,
a speed much over 4 (if I recall correctly) would put
the shock from the nose in the inlets. Bad news.

On 29 Nov 2003 12:48:59 -0800, (frank wight)
wrote:

There was a time when I thought that
the blackbird could secretly hit 5 on the
mach meter--but isn't there solid science
agains this? Such as:

If you go faster than Mach 3.5 the bow shock off the nose will impinge
on the leading edge of the outboard section of the wing and melt it
off if you do it for very long. It's OK for a dash, but not for
cruise. That's pretty solid science.

I don't think the engines have the ability
to rev up to such a speed. Maybe the jet fuel
itself cannot produce sufficent BTU's (thrust)
to propel it that fast, maybe the fuel lines
are too small to exceed Mach 3.3

The SR-71 has dashed to Mach 3.5, so this isn't a problem.

Mary

--
Mary Shafer Retired aerospace research engineer

On Sat, 29 Nov 2003 19:54:46 -0800, Mary Shafer
wrote:

On 29 Nov 2003 12:48:59 -0800, (frank wight)
wrote:

There was a time when I thought that
the blackbird could secretly hit 5 on the
mach meter--but isn't there solid science
agains this? Such as:

If you go faster than Mach 3.5 the bow shock off the nose will impinge
on the leading edge of the outboard section of the wing and melt it
off if you do it for very long. It's OK for a dash, but not for
cruise. That's pretty solid science.


You know out of all the "how fast will it REALLY go" discussions
that's the first time I've heard an answer that satisfied me. Many
here are familiar with that X-15 that burned off it's ventral fin from
shock inpingment from that test ramjet. Most of the answers I'd
heard in the past for why it can't go a lot faster than 3.2 is
"because it can't". The shock thing makes total sense. I'd read that
one of the A-12s hit 3.6 at 97,600 which is probably close to the
alltime best. It's definitely the best I've ever seen published.

(frank wight) wrote in message . com...
There was a time when I thought that
the blackbird could secretly hit 5 on the
mach meter--but isn't there solid science
agains this? Such as:

I don't think the engines have the ability
to rev up to such a speed. Maybe the jet fuel
itself cannot produce sufficent BTU's (thrust)
to propel it that fast, maybe the fuel lines
are too small to exceed Mach 3.3

Perhaps the real inhibitor is the lack of
enough combustible oxygen to feed the engines
to shatter established speed records.

I know that the outer metal shell of the
jet couldn't sustain the high atmospheric
friction.

Am I right about all this, or is there OTHER
things to consider?


The SR71 is limited in speed by the shock wave from the nose of the
aircraft impinging on the inlet lip of the engines over about Mach
3.5. The dash speed of the aircraft is not limited by either engine
thrust or or short term thermal issues.

Theoreticaly the A12 should be faster becuase of its shorter nose.

In article ,
(The Enlightenment) writes:
(frank wight) wrote in message . com...
There was a time when I thought that
the blackbird could secretly hit 5 on the
mach meter--but isn't there solid science
agains this? Such as:

I don't think the engines have the ability
to rev up to such a speed. Maybe the jet fuel
itself cannot produce sufficent BTU's (thrust)
to propel it that fast, maybe the fuel lines
are too small to exceed Mach 3.3

Perhaps the real inhibitor is the lack of
enough combustible oxygen to feed the engines
to shatter established speed records.

I know that the outer metal shell of the
jet couldn't sustain the high atmospheric
friction.

Am I right about all this, or is there OTHER
things to consider?


The SR71 is limited in speed by the shock wave from the nose of the
aircraft impinging on the inlet lip of the engines over about Mach
3.5. The dash speed of the aircraft is not limited by either engine
thrust or or short term thermal issues.

Theoreticaly the A12 should be faster becuase of its shorter nose.

Uhm, Bernie - If one of the limiting factors in an A-12/SR-71's speed
is shock impingement, (Which it is, a;though IIRC it's shoc
impingement on the leading edges of the wings, not the nacelles), how
is a shorter nose going to give you a higher Mach Number? A longer
nose would allow a steeper included angle. (Y'know, all that Opposite
vs. Adjacent stuff from High School Trig.) Unless, of course, Shock
Waves work backwards in Australia?

--
Pete Stickney
A strong conviction that something must be done is the parent of many
bad measures. -- Daniel Webster

(Peter Stickney) wrote in message ...
In article ,
(The Enlightenment) writes:
(frank wight) wrote in message . com...
SNIP

The SR71 is limited in speed by the shock wave from the nose of the
aircraft impinging on the inlet lip of the engines over about Mach
3.5. The dash speed of the aircraft is not limited by either engine
thrust or or short term thermal issues.

Theoreticaly the A12 should be faster becuase of its shorter nose.

Uhm, Bernie -

Frederick actualy. Bernxard is my spanish blue cat. I use his email.

If one of the limiting factors in an A-12/SR-71's speed
is shock impingement, (Which it is, a;though IIRC it's shoc
impingement on the leading edges of the wings, not the nacelles), how
is a shorter nose going to give you a higher Mach Number? A longer
nose would allow a steeper included angle. (Y'know, all that Opposite
vs. Adjacent stuff from High School Trig.) Unless, of course, Shock
Waves work backwards in Australia?

You got me there.

The shockwave story re impingingment on the nacels I though I read in
a review of sled driver published in Air International.

Are you sure its wing tips? The solution I think is in a protractor
and a photocopy of and SR71 outline.

In article ,
(The Enlightenment) writes:
(Peter Stickney) wrote in message ...
In article ,
(The Enlightenment) writes:
(frank wight) wrote in message . com...
SNIP

The SR71 is limited in speed by the shock wave from the nose of the
aircraft impinging on the inlet lip of the engines over about Mach
3.5. The dash speed of the aircraft is not limited by either engine
thrust or or short term thermal issues.

Theoreticaly the A12 should be faster becuase of its shorter nose.

Uhm, Bernie -

Frederick actualy. Bernxard is my spanish blue cat. I use his email.

But it's pronounced Raymond Luxury-Yacht.
Bright cat.

If one of the limiting factors in an A-12/SR-71's speed
is shock impingement, (Which it is, a;though IIRC it's shoc
impingement on the leading edges of the wings, not the nacelles), how
is a shorter nose going to give you a higher Mach Number? A longer
nose would allow a steeper included angle. (Y'know, all that Opposite
vs. Adjacent stuff from High School Trig.) Unless, of course, Shock
Waves work backwards in Australia?

You got me there.

The shockwave story re impingingment on the nacels I though I read in
a review of sled driver published in Air International.

Are you sure its wing tips? The solution I think is in a protractor
and a photocopy of and SR71 outline.

Yep. That's how I figured it out. The wingtips would be impinged upon
first, then the chines on the outboard sides of the nacelles, then the
outer nafelle lip. Of course, you'd get some complicated shock
interactions going on in the region of the nacelle, so simple
straightedge and protracter stuff is only approximate.

There's a whole bunch of stuff going on that would limit the max speed
to somewhere between Mach 3.2 - 3.5. The shock impingement stuff, the
air temperature at the compressor face, the ability of the fuel to
carry heat away from critical components pop into mind at a first
stab. Those factors all meet at or about Mach 3.5.

--
Pete Stickney
A strong conviction that something must be done is the parent of many
bad measures. -- Daniel Webster