Refuting blackbird folklore

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

Mary Shafer wrote in message . ..
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.

The ablative compound Martin MA-25S AND the white sealant worked
together to get the X-15A-2 up to its record speed. This combo was
proposed for the SR-71 at one time but rejected. MA-25S, however, was
used on the space shuttle and other white compounds have been tested
for high speed flight.

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

Funny how the all-white Mach 3 XB-70 seemed to hold up to kinetic
heating all right... and that was just simple nuclear anti-flash
white.

Rob

On 30 Nov 2003 18:10:14 -0800, (robert arndt) wrote:

Mary Shafer wrote in message . ..
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.

The ablative compound Martin MA-25S AND the white sealant worked
together to get the X-15A-2 up to its record speed. This combo was
proposed for the SR-71 at one time but rejected. MA-25S, however, was
used on the space shuttle and other white compounds have been tested
for high speed flight.

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

Funny how the all-white Mach 3 XB-70 seemed to hold up to kinetic
heating all right... and that was just simple nuclear anti-flash
white.

Rob


For the record according to Ben Rich in the book Skunk Works the black
paint lowered the temperature by 30 degrees and was done in order to
let them use an easier to work with kind of titanium. (Hey just
passing on what I read.)

(robert arndt) wrote:

Funny how the all-white Mach 3 XB-70 seemed to hold up to kinetic
heating all right... and that was just simple nuclear anti-flash
white.

They did that by using a fairly scary system of pipes that ran through
high-heat areas, and used the plane's fuel as a heat sink, combined with
extensive use of titanium in the worst spots.

In a combat-ready version, you can safely assume that they would have
used the "iron ball" black paint for radar reduction and heat protection.

--
cirby at cfl.rr.com

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

On Mon, 01 Dec 2003 04:24:22 GMT, Chad Irby wrote:

(robert arndt) wrote:

Funny how the all-white Mach 3 XB-70 seemed to hold up to kinetic
heating all right... and that was just simple nuclear anti-flash
white.

They did that by using a fairly scary system of pipes that ran through
high-heat areas, and used the plane's fuel as a heat sink, combined with
extensive use of titanium in the worst spots.

Not to mention the 4000 gallon tank of water. (It might have been 4000
pounds not gallons but I'm fairly certain it was gallons. They also
had an additional tank with ammonia just in case the water ran out)




In a combat-ready version, you can safely assume that they would have
used the "iron ball" black paint for radar reduction and heat protection.

Chad Irby wrote in message . com...
(robert arndt) wrote:

Funny how the all-white Mach 3 XB-70 seemed to hold up to kinetic
heating all right... and that was just simple nuclear anti-flash
white.

They did that by using a fairly scary system of pipes that ran through
high-heat areas, and used the plane's fuel as a heat sink, combined with
extensive use of titanium in the worst spots.

In a combat-ready version, you can safely assume that they would have
used the "iron ball" black paint for radar reduction and heat protection.

"Iron Ball" black paint was derived from the Third Reich's
radar-absorbing "Schornsteinfeger" (Chimney Sweep) carbon paint meant
for the Go-229 jet flying wing.

Rob