Refuting blackbird folklore

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?

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?

A lot of that is pretty much on the mark. I've heard Mach 3.5 for short
sprints, but not more than 3.3 for sustained flight.

Mach 5? No way in hell, although I've seen a very few claims for Mach 4
sprints (extremely informally on that one). Even if they could manage
the power to do it, the skin would be melting (see the thread on the
Sanger Amerika Bomber for some of the problems with sustained very high
speed flight).

--
cirby at cfl.rr.com

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

Chad Irby wrote in message ...
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?

A lot of that is pretty much on the mark. I've heard Mach 3.5 for short
sprints, but not more than 3.3 for sustained flight.

Mach 5? No way in hell, although I've seen a very few claims for Mach 4
sprints (extremely informally on that one). Even if they could manage
the power to do it, the skin would be melting (see the thread on the
Sanger Amerika Bomber for some of the problems with sustained very high
speed flight).

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.

Rob

owever, the airframe of the SR-71 is stressed for Mach 4.0
flight.


Where did you hear that?

Scott Ferrin wrote in message . ..
owever, the airframe of the SR-71 is stressed for Mach 4.0
flight.


Where did you hear that?

From a credible Beale AFB source. I should mention that Mach 4.0 is
beyond the Blackbird's "stability limit" of Mach 3.5.
A typical mission for the Blackbird would be Mach 3.2 at 85,000 ft.
The aircraft could safely raise the speed from Mach 3.2 to 3.3 and
accellerate up to Mach 3.5 (the stability limit)for a limited time.
Pushing the aircraft up past 3.5 in an emergency was possible but not
recommended. The airframe could handle limited endurance up to Mach
4.0 with the penalty of damaging the aircraft/engines at sustained
flight at that speed.
The MiG-25 Foxbat had a similar stability limit of Mach 2.83. The lone
Foxbat chased by the Israelis up to Mach 3.2 suffered severe damage to
the engines as a result of exceeding the stability limit. MiG-25
pilots were instructed not to attempt speeds over Mach 2.5-2.6, with
special permission required for emergency dash at Mach 2.80. After
that the aircraft could easily still accelerate but the engines would
begin to suffer damage.
The radar absorbing paint on the SR-71 also acted as a heat sink,
lowering the airframe temperature by nearly 100 degrees. It would have
been better, however, if the aircraft was painted white overall
instead of blue-black. This was proposed at least once (based on the
X-15 research) but rejected.

Rob

On 30 Nov 2003 09:08:15 -0800, (robert arndt) wrote:

Scott Ferrin wrote in message . ..
owever, the airframe of the SR-71 is stressed for Mach 4.0
flight.


Where did you hear that?

From a credible Beale AFB source. I should mention that Mach 4.0 is
beyond the Blackbird's "stability limit" of Mach 3.5.
A typical mission for the Blackbird would be Mach 3.2 at 85,000 ft.
The aircraft could safely raise the speed from Mach 3.2 to 3.3 and
accellerate up to Mach 3.5 (the stability limit)for a limited time.

I'm skeptical about the 3.5. On of the A-12s hit 3.6 at 97,000 ft.
during testing.

On 30 Nov 2003 09:08:15 -0800, (robert arndt) wrote:

The radar absorbing paint on the SR-71 also acted as a heat sink,
lowering the airframe temperature by nearly 100 degrees. It would have
been better, however, if the aircraft was painted white overall
instead of blue-black. This was proposed at least once (based on the
X-15 research) but rejected.

No. The SR-71 is black because that improves its ability to radiate
away heat. Remember sigma x T**4? Well, sigma is higher for this
black paint than it is for white paint.

The X-15 never did any research on white paint. If you're thinking of
the white paint used to protect the pink ablative coating on #2, that
wasn't there to improve radiation and it burned off very quickly.
There was nothing significant about the paint color.

Since the X-15 flew a really quick trajectory, rather than cruising at
high speeds, color was much less of an issue. It wasn't in the air
long enough for radiation to help. (The same is true for the Space
Shuttle Orbiter.) However, the SR-71 cruised at high speeds and
radiation helped lower the temperature, as you mention.

Where do you think the heat absorbed by the paint went? Heat can be
conducted into the airframe, convected into the air, or radiated into
space. It doesn't just vanish into the molecules of the paint. The
surface of the airplane, covered with paint, radiated that heat
outward. The heat came from more than just the paint; it also came
from the skin and structure.

Mary

--
Mary Shafer Retired aerospace research engineer

"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.

On Sun, 30 Nov 2003 07:21:36 -0500, "Brian"
wrote:


"robert arndt" wrote in message
. com...
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.

Even back in the day there are some they couldn't ignore. If you
counted both sides I'd give the SA-5, Nike Hercules and Bomarc B fair
odds.

Scott Ferrin wrote in message . ..
On Sun, 30 Nov 2003 07:21:36 -0500, "Brian"
wrote:


"robert arndt" wrote in message
. com...
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.

Even back in the day there are some they couldn't ignore. If you
counted both sides I'd give the SA-5, Nike Hercules and Bomarc B fair
odds.


Not being able to ignore them (i.e., SA-5), yes. But "fair odds"? I
don't think I'd go that far. A tail chase was unlikely to work (it
took a great deal of energy to get the SAM up to that altitude, not
leaving a lot for subsequent catch up or maneuver). A head-on shot
required a targeting system capable of handling the extreme closure
velocity along with again leaving enough energy to maneuver to the
kill. Possible, but not really likely I'd think. Nike Herc I'd place
in the "very lucky shot" category, unless the nuclear warhead version
was used (unlikely to say the least), and BOMARC in the "when pigs
fly" category (again unless the nuke model was used)--it had the
altitude (but only by challenging its capabilities--its ceiling was
about 100K), but lacked the energy (it could only do about M 3.0
itself).

Brooks