Re: XB-70 vs B-2

[Ragnar]

"Hobo" > wrote in message
...
>
> Would it have made more sense to have built the XB-70 instead of the
> B-2? With its speed and high altitude ability the XB-70 would have had
> much of the survivability of the B-2, perhaps at a lower cost. The XB-70
> would also have been less vulnerable to technological change. A single
> big advance in sensor technology could make the B-2 a sitting duck, but
> the XB-70 will always have its Mach 3 speed to rely on. In terms of
> cost/performance, wouldn't the XB-70 have been able to do the same job
> at a lower price?

The SA-12 goes up to about 100,000 feet and does at least Mach 6. Think the
XB-70 could handle that?

[Thomas J. Paladino Jr.]

"Hobo" > wrote in message
...
>
> Would it have made more sense to have built the XB-70 instead of the
> B-2? With its speed and high altitude ability the XB-70 would have had
> much of the survivability of the B-2, perhaps at a lower cost. The XB-70
> would also have been less vulnerable to technological change. A single
> big advance in sensor technology could make the B-2 a sitting duck, but
> the XB-70 will always have its Mach 3 speed to rely on. In terms of
> cost/performance, wouldn't the XB-70 have been able to do the same job
> at a lower price?

Well, yes and no. The XB-70 was indeed a marvel, and would probably be very
useful in *today's* military, however lets put the situation in context.

At the time (1955), all of our weapons systems were being designed to
counter the soviet threat. It was originally thought that 'high and fast'
would be a great combination for a bomber to evade soviet defenses, i.e. the
SR-71. However, the shoot-down of the U2 over soviet terratory demonstrated
that their SAM technologies were capable of hitting high altitude targets.
And while no SR-71 was ever taken down, even the Blackbird had a couple of
*very* close calls with soviet SAMs.

Now although the XB-70 flew high and fast, it was neither as high, nor as
fast as the SR-71 (M3.0 @ 72k vs. M3.2+ @ 85k+). Take into account it's
massive radar signature and the fact that at mach 3 the aircraft was not
terribly manuverable, flying an essentially straight-line trajectory; and it
became a simple matter of mathmatics to see that it would probably not be
all that hard for the soviets to hit. (Hence it's cancellation). Stealth
technology was seen (and rightly so) as the single greatest option for
penetrating soviet air defenses.

Of course, today there is no soviet threat, and indeed no threat with the
SAM capabilities once posessed by the soviets, so the XB-70 would probably
be well suited to many of today's missions; unfortunately in 1955 it was
impossible to predict. However the B-2 is a highly useful and important
asset, and will remain so for the forseeable future. It will take much more
than a single advance in sensor technology to make it obsolete; trust me,
many have been working towards that goal for almost two decades now, and we
haven't been sitting on our hands here either. The B-2 was a good
investment, and will be around for a while.

Thomas J. Paladino
New York City

[B2431]

>From: Hobo
>Date: 12/17/2003 11:37 PM Central Standard Time
>Message-id: >
>
>
>Would it have made more sense to have built the XB-70 instead of the
>B-2? With its speed and high altitude ability the XB-70 would have had
>much of the survivability of the B-2, perhaps at a lower cost. The XB-70
>would also have been less vulnerable to technological change. A single
>big advance in sensor technology could make the B-2 a sitting duck, but
>the XB-70 will always have its Mach 3 speed to rely on. In terms of
>cost/performance, wouldn't the XB-70 have been able to do the same job
>at a lower price?
>
The XB-70 had no low altiotude mission capability.

Dan, U. S. Air Force, retired

[steve gallacci]

As others have pointed out, the B-70 would have been vulnerable to SAMs,
especially as those missiles dedicated to strategic defense would have
been nuclear armed. And the B-70 would have been awfully expensive to
operate for conventional ops. But wouldn't have it been so Cool!

[B2431]

>From: (B2431)

>>
>The XB-70 had no low altiotude mission capability.
>
>Dan, U. S. Air Force, retired
>

Egad, tarver's spelling has rubbed off on me.

Dan, U.S. Air Force, retired

[Tarver Engineering]

"B2431" > wrote in message
...
> >From: (B2431)
>
> >>
> >The XB-70 had no low altiotude mission capability.

> Egad, tarver's spelling has rubbed off on me.

Being able to spell is the last thing you had, Dan, so sorry.

[John R Weiss]

"Hobo" > wrote...
>
> Would it have made more sense to have built the XB-70 instead of the
> B-2? With its speed and high altitude ability the XB-70 would have had
> much of the survivability of the B-2, perhaps at a lower cost. The XB-70
> would also have been less vulnerable to technological change. A single
> big advance in sensor technology could make the B-2 a sitting duck, but
> the XB-70 will always have its Mach 3 speed to rely on. In terms of
> cost/performance, wouldn't the XB-70 have been able to do the same job
> at a lower price?

The MiG-25 was designed specifically to counter the B-70. It also would have
been somewhat vulnerable to the SA-5. I suspect technological advances on both
sides would have kept it somewhat vulnerable at any given time.

Also, the payload for which the B-70 was designed no longer exists -- it was
obsolete almost before the XB-70 flew. Whether the B-70 would have been
suitable for the smaller nukes, ALCMs, and other modern weapons would make for
an interesting discussion. At first glance, the B-1 was a feeble attempt to
replicate the B-70 concept, using smaller payloads and MANY fewer $$...

[Smartace11]

>Also, the payload for which the B-70 was designed no longer exists -- it was
>obsolete almost before the XB-70 flew. Whether the B-70 would have been
>suitable for the smaller nukes, ALCMs, and other modern weapons would make
>for
>an interesting discussion. At first glance, the B-1 was a feeble attempt to
>replicate the B-70 concept, using smaller payloads and MANY fewer $$...
>
>
>
>
>
>
>

I imagine a mod to carry anything conventional besides dumb bombs would have
been cost prohibitive with the state of art electronics a 1950s airplane had.

[Felger Carbon]

"John R Weiss" > wrote in message
news:dQoEb.145855$_M.717065@attbi_s54...
>
> The MiG-25 was designed specifically to counter the B-70.

Correct. Wasn't the B-70 killer missile the Mig-25 was designed to
carry called the "Anab"? 40 feet long IIRC. Huge mutha.

Besides that, the B-70 program was dimmed further by breaking
developments in ICBM range/payload and also inertial guidance
developments out of the Charles Stark Draper Labs at MIT, and the
(sorta) commercial development of same by Northrup in the greater
Boston area (Norwood?).

[John R Weiss]

"Smartace11" > wrote...
>
> I imagine a mod to carry anything conventional besides dumb bombs would have
> been cost prohibitive with the state of art electronics a 1950s airplane had.

Dunno... An airplane as big as the B-70, with LOTS of space for black boxes and
wiring, might have lent itself fairly well to modern electronics with their
smaller boxes. Look at all the warts and gizmos the B-52 has grown, externally
and internally, in the past 40+ years...

If the Buff can be adapted to JDAM, JSOW, and ALCM, why not the B-70? Filling
the big, open bomb bay with racks or launchers and/or fuel tanks like the B-52
or B-1 might not be that hard...

OTOH, the local flow and weapon separation problems at Mach 3 would be
"interesting" for smaller weapons...

[breyfogle]

The XB-70 had one large weapons bay and a payload rating of 50,000 pounds.
The B-1B, at about 2/3 the max gross weight of the XB-70, carried a larger
payload with its three 20,000 pound weapons bays plus the ability to carry
another 30,000 pounds externally. Hardly feeble .... Designing for Mach 3
using 1950's technology resulted in a much smaller payload as a fraction of
the gross weight than any newer design. Concourde suffered the same payload
inefficiency.

"John R Weiss" > wrote in message
news:dQoEb.145855$_M.717065@attbi_s54...
> "Hobo" > wrote...
> >
> > Would it have made more sense to have built the XB-70 instead of the
> > B-2? With its speed and high altitude ability the XB-70 would have had
> > much of the survivability of the B-2, perhaps at a lower cost. The XB-70
> > would also have been less vulnerable to technological change. A single
> > big advance in sensor technology could make the B-2 a sitting duck, but
> > the XB-70 will always have its Mach 3 speed to rely on. In terms of
> > cost/performance, wouldn't the XB-70 have been able to do the same job
> > at a lower price?
>
> The MiG-25 was designed specifically to counter the B-70. It also would
have
> been somewhat vulnerable to the SA-5. I suspect technological advances on
both
> sides would have kept it somewhat vulnerable at any given time.
>
> Also, the payload for which the B-70 was designed no longer exists -- it
was
> obsolete almost before the XB-70 flew. Whether the B-70 would have been
> suitable for the smaller nukes, ALCMs, and other modern weapons would make
for
> an interesting discussion. At first glance, the B-1 was a feeble attempt
to
> replicate the B-70 concept, using smaller payloads and MANY fewer $$...
>

[Mike Beede]

In article >, Smartace11 > wrote:

> I imagine a mod to carry anything conventional besides dumb bombs would have
> been cost prohibitive with the state of art electronics a 1950s airplane had.

I think you meant "1960s". By the time it was in service, it would have probably
been nearly the 70s.

Mike Beede

[WaltBJ]

The B70 was doomed once its IR signature was analyzed. Even the B58 at
M2.0 had an IR signature the 102's poor old LN2 cooled seeker head
could detect about 100 miles away. And we found the IR Falcons could
track the B58, too. At least the IR WESM (Weapons System Evaluator
Missile) brought back tapes showing the missile seeker head was locked
on and tracking - during a frontal attack. Now, A B70 at M3.0 and
+75000 would be like a giant IR beacon with a radar signature like the
Vertical Assembly Building, all screaming 'Shoot Me'.
Walt BJ

[Chad Irby]

In article >,
(WaltBJ) wrote:

> The B70 was doomed once its IR signature was analyzed. Even the B58 at
> M2.0 had an IR signature the 102's poor old LN2 cooled seeker head
> could detect about 100 miles away. And we found the IR Falcons could
> track the B58, too. At least the IR WESM (Weapons System Evaluator
> Missile) brought back tapes showing the missile seeker head was locked
> on and tracking - during a frontal attack. Now, A B70 at M3.0 and
> +75000 would be like a giant IR beacon with a radar signature like the
> Vertical Assembly Building, all screaming 'Shoot Me'.

The only problem with high-speed IR missiles over long ranges is that
the window in the front of the seeker head gets hot enough to blind the
warhead. The same factors that make the B70 an IR beacon make the
missile itself one, too, unless you keep the speed down (which cuts back
on the effectiveness of the missile, even in head-on encounters).

Now, a ground-based IR acquisition system could be very nice for such a
high, fast plane, with a radar-based terminal guidance system for the
missile itself, avoiding the IR issues.

--
cirby at cfl.rr.com

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

[Steve Hix]

In article >,
Hobo > wrote:

> Would it have made more sense to have built the XB-70 instead of the
> B-2? With its speed and high altitude ability the XB-70 would have had
> much of the survivability of the B-2, perhaps at a lower cost.

Before the B-70's first flight, it was clear that SAM technology, both
Russian and Western, was more than up to the task of knocking it down.

Which is why no production Valkyries were built.

[Nele VII]

MiG-25 was not designed to counter B-70, but to intercept A-12 and SR-71.
At least Rostislav Belyakov, MiG-25 the chief engineer of MiG stated...
--

Nele

NULLA ROSA SINE SPINA
John R Weiss wrote in message ...
>"Hobo" > wrote...
>>
>> Would it have made more sense to have built the XB-70 instead of the
>> B-2? With its speed and high altitude ability the XB-70 would have had
>> much of the survivability of the B-2, perhaps at a lower cost. The XB-70
>> would also have been less vulnerable to technological change. A single
>> big advance in sensor technology could make the B-2 a sitting duck, but
>> the XB-70 will always have its Mach 3 speed to rely on. In terms of
>> cost/performance, wouldn't the XB-70 have been able to do the same job
>> at a lower price?
>
>The MiG-25 was designed specifically to counter the B-70. It also would
have
>been somewhat vulnerable to the SA-5. I suspect technological advances on
both
>sides would have kept it somewhat vulnerable at any given time.
>
>Also, the payload for which the B-70 was designed no longer exists -- it
was
>obsolete almost before the XB-70 flew. Whether the B-70 would have been
>suitable for the smaller nukes, ALCMs, and other modern weapons would make
for
>an interesting discussion. At first glance, the B-1 was a feeble attempt
to
>replicate the B-70 concept, using smaller payloads and MANY fewer $$...
>

[BOB URZ]

Ragnar wrote:

> "Hobo" > wrote in message
> ...
> >
> > Would it have made more sense to have built the XB-70 instead of the
> > B-2? With its speed and high altitude ability the XB-70 would have had
> > much of the survivability of the B-2, perhaps at a lower cost. The XB-70
> > would also have been less vulnerable to technological change. A single
> > big advance in sensor technology could make the B-2 a sitting duck, but
> > the XB-70 will always have its Mach 3 speed to rely on. In terms of
> > cost/performance, wouldn't the XB-70 have been able to do the same job
> > at a lower price?
>
> The SA-12 goes up to about 100,000 feet and does at least Mach 6. Think the
> XB-70 could handle that?

You could make a case for a Sam being able to knock out any airplane. So why
build any at all?

Assuming B70's were built and upgraded umpteen times by now,
what do you think the results would be with a re-engine of the six pack with a
modern supercruise engine such as a F119?

Bob



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[Chad Irby]

In article >,
BOB URZ > wrote:

> Assuming B70's were built and upgraded umpteen times by now,
> what do you think the results would be with a re-engine of the six pack with a
> modern supercruise engine such as a F119?

Since the engines used in the F-23 have about 85% of the thrust in
cruise as the B-70 engines in full afterburner, it sorta makes you
wonder about the range...

--
cirby at cfl.rr.com

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

[Ragnar]

"BOB URZ" > wrote in message
...
>
>
> Ragnar wrote:
>
> > "Hobo" > wrote in message
> > ...
> > >
> > > Would it have made more sense to have built the XB-70 instead of the
> > > B-2? With its speed and high altitude ability the XB-70 would have had
> > > much of the survivability of the B-2, perhaps at a lower cost. The
XB-70
> > > would also have been less vulnerable to technological change. A single
> > > big advance in sensor technology could make the B-2 a sitting duck,
but
> > > the XB-70 will always have its Mach 3 speed to rely on. In terms of
> > > cost/performance, wouldn't the XB-70 have been able to do the same job
> > > at a lower price?
> >
> > The SA-12 goes up to about 100,000 feet and does at least Mach 6. Think
the
> > XB-70 could handle that?
>
> You could make a case for a Sam being able to knock out any airplane. So
why
> build any at all?

Poor logic on your part. An SA-2 or 3 would have no chance of engaging an
XB-70, but an SA-10 or 12 would. The point is that the XB-70 was designed
to encounter those early missiles. Unfortunately, later missiles like the
SA-5 were already in development at the time and its the future threat, not
the current threat, that killed the XB-70.

> Assuming B70's were built and upgraded umpteen times by now,
> what do you think the results would be with a re-engine of the six pack
with a
> modern supercruise engine such as a F119?

It would look really cool, but it wouldn't go any faster.

[Scott Ferrin]

>You could make a case for a Sam being able to knock out any airplane. So why
>build any at all?
>
>Assuming B70's were built and upgraded umpteen times by now,
>what do you think the results would be with a re-engine of the six pack with a
>modern supercruise engine such as a F119?
>
>Bob

Actually I'd be surprised if the F119 powered one wasn't *slower*.
The J93 was designed for Mach 3 and high altitudes. The F119 is not.

[Bob Martin]

> > The MiG-25 was designed specifically to counter the B-70.
>
> Correct. Wasn't the B-70 killer missile the Mig-25 was designed to
> carry called the "Anab"? 40 feet long IIRC. Huge mutha.


No... the MiG-25 had the R-40 missile (NATO name AA-6 "Acrid"). And
it was only about 20 feet long.

FAS has a couple pictures... I wouldn't take their range and
performance data seriously (on anything), but as far as physical
dimensions they seem to be in the ballpark.

http://www.fas.org/man/dod-101/sys/missile/row/aa-6.htm

[Felger Carbon]

"Bob Martin" > wrote in message
om...
> > > The MiG-25 was designed specifically to counter the B-70.
> >
> > Correct. Wasn't the B-70 killer missile the Mig-25 was designed
to
> > carry called the "Anab"? 40 feet long IIRC. Huge mutha.
>
>
> No... the MiG-25 had the R-40 missile (NATO name AA-6 "Acrid"). And
> it was only about 20 feet long.
>
> FAS has a couple pictures... I wouldn't take their range and
> performance data seriously (on anything), but as far as physical
> dimensions they seem to be in the ballpark.
>
> http://www.fas.org/man/dod-101/sys/missile/row/aa-6.htm

Thanx for the correction, Bob. It's been too long since this old fart
looked up that data. ;-)

But since the Mig-25 was designed to attack at high speeds (and at
high speeds everything, attacker and attackee, travels in a straight
line), the Mig-25 had small tailfeathers and hence low manuevrebility
(sp?). So, it's intended target gone, the 25 became a photorecon
platform. It and the later Mig-31 Foxhound in effect became the
Soviet's SR-71.

Was the AA-6 Acrid missile dropped, or was it "retargeted"?

[Scott Ferrin]

On Fri, 19 Dec 2003 05:07:37 GMT, Chad Irby > wrote:

>In article >,
> (WaltBJ) wrote:
>
>> The B70 was doomed once its IR signature was analyzed. Even the B58 at
>> M2.0 had an IR signature the 102's poor old LN2 cooled seeker head
>> could detect about 100 miles away. And we found the IR Falcons could
>> track the B58, too. At least the IR WESM (Weapons System Evaluator
>> Missile) brought back tapes showing the missile seeker head was locked
>> on and tracking - during a frontal attack. Now, A B70 at M3.0 and
>> +75000 would be like a giant IR beacon with a radar signature like the
>> Vertical Assembly Building, all screaming 'Shoot Me'.
>
>The only problem with high-speed IR missiles over long ranges is that
>the window in the front of the seeker head gets hot enough to blind the
>warhead.

The AIM-47 Falcon had something like a hundred mile range and flew at
Mach 6. It had IR terminal guidance. Today's THAAD uses IR also
(several others do but they use kill vehicles that are protected
before the leave the atmosphere). HEDI also used an IR terminal
guidance. Think of HEDI as a hit-to-kill Sprint missile. I don't
know if they ever did get the IR seeker to work though. ISTR it was
cooled by nitrogen gas flowing over the outside of the seeker and used
a synthetic sapphire window.

[Bjørnar Bolsøy]

(Bob Martin) wrote in
om:

>> > The MiG-25 was designed specifically to counter the B-70.
>>
>> Correct. Wasn't the B-70 killer missile the Mig-25 was
>> designed to carry called the "Anab"? 40 feet long IIRC. Huge
>> mutha.
>
>
> No... the MiG-25 had the R-40 missile (NATO name AA-6 "Acrid").
> And it was only about 20 feet long.
>
> FAS has a couple pictures... I wouldn't take their range and
> performance data seriously (on anything), but as far as physical
> dimensions they seem to be in the ballpark.
>
> http://www.fas.org/man/dod-101/sys/missile/row/aa-6.htm

Interesting to note that the images depict the IR version,
except the mid bottom image, which shows the usual mix
of IR on the two inner pylons and radar seekers on the
two outboard pylons.


Regards...

[Scott Ferrin]

On Sat, 20 Dec 2003 19:17:34 GMT, "Felger Carbon" >
wrote:

>"Bob Martin" > wrote in message
om...
>> > > The MiG-25 was designed specifically to counter the B-70.
>> >
>> > Correct. Wasn't the B-70 killer missile the Mig-25 was designed
>to
>> > carry called the "Anab"? 40 feet long IIRC. Huge mutha.
>>
>>
>> No... the MiG-25 had the R-40 missile (NATO name AA-6 "Acrid"). And
>> it was only about 20 feet long.
>>
>> FAS has a couple pictures... I wouldn't take their range and
>> performance data seriously (on anything), but as far as physical
>> dimensions they seem to be in the ballpark.
>>
>> http://www.fas.org/man/dod-101/sys/missile/row/aa-6.htm
>
>Thanx for the correction, Bob. It's been too long since this old fart
>looked up that data. ;-)
>
>But since the Mig-25 was designed to attack at high speeds (and at
>high speeds everything, attacker and attackee, travels in a straight
>line), the Mig-25 had small tailfeathers and hence low manuevrebility
>(sp?). So, it's intended target gone, the 25 became a photorecon
>platform. It and the later Mig-31 Foxhound in effect became the
>Soviet's SR-71.
>
>Was the AA-6 Acrid missile dropped, or was it "retargeted"?
>


They use the AA-9 (Phoenix ripoff) as the main armament on the Mig-31
although the AA-6 is also shown in some pictures.

[BOB URZ]

Scott Ferrin wrote:

> >You could make a case for a Sam being able to knock out any airplane. So why
> >build any at all?
> >
> >Assuming B70's were built and upgraded umpteen times by now,
> >what do you think the results would be with a re-engine of the six pack with a
> >modern supercruise engine such as a F119?
> >
> >Bob
>
> Actually I'd be surprised if the F119 powered one wasn't *slower*.
> The J93 was designed for Mach 3 and high altitudes. The F119 is not.

I realize that airflow and inlet geometry are critical for a high
mach plane, but what would be different in the guts of the engine?
Did the XB-70 burn a non standard fuel like the SR71?

I suppose my point was expanded range or payload using the
F119. Who knows, maybe there is a orphan XB70 made out
of spare parts laying around groom lake somewhere.
Might be an interesting platform to test some of the new high
tech aero spike or pulse engines.

Bob



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[Chad Irby]

In article >,
Scott Ferrin > wrote:

> On Fri, 19 Dec 2003 05:07:37 GMT, Chad Irby > wrote:
>
> >In article >,
> > (WaltBJ) wrote:
> >
> >> The B70 was doomed once its IR signature was analyzed. Even the B58 at
> >> M2.0 had an IR signature the 102's poor old LN2 cooled seeker head
> >> could detect about 100 miles away. And we found the IR Falcons could
> >> track the B58, too. At least the IR WESM (Weapons System Evaluator
> >> Missile) brought back tapes showing the missile seeker head was locked
> >> on and tracking - during a frontal attack. Now, A B70 at M3.0 and
> >> +75000 would be like a giant IR beacon with a radar signature like the
> >> Vertical Assembly Building, all screaming 'Shoot Me'.
> >
> >The only problem with high-speed IR missiles over long ranges is that
> >the window in the front of the seeker head gets hot enough to blind the
> >warhead.
>
> The AIM-47 Falcon had something like a hundred mile range and flew at
> Mach 6. It had IR terminal guidance. Today's THAAD uses IR also
> (several others do but they use kill vehicles that are protected
> before the leave the atmosphere). HEDI also used an IR terminal
> guidance. Think of HEDI as a hit-to-kill Sprint missile. I don't
> know if they ever did get the IR seeker to work though. ISTR it was
> cooled by nitrogen gas flowing over the outside of the seeker and used
> a synthetic sapphire window.

Yeah, you have to do some serious redesign to make IR a good high-speed
targeting method. It's just easier to do it the other way around for
the sort of target we're looking at - superfast, very high.

The AIM-47 never really worked that well, though they used some of the
lessons learned to make the AIM-54 Phoenix... without the IR.

--
cirby at cfl.rr.com

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

[Scott Ferrin]

On Sat, 20 Dec 2003 21:23:42 GMT, Chad Irby > wrote:

>In article >,
> Scott Ferrin > wrote:
>
>> On Fri, 19 Dec 2003 05:07:37 GMT, Chad Irby > wrote:
>>
>> >In article >,
>> > (WaltBJ) wrote:
>> >
>> >> The B70 was doomed once its IR signature was analyzed. Even the B58 at
>> >> M2.0 had an IR signature the 102's poor old LN2 cooled seeker head
>> >> could detect about 100 miles away. And we found the IR Falcons could
>> >> track the B58, too. At least the IR WESM (Weapons System Evaluator
>> >> Missile) brought back tapes showing the missile seeker head was locked
>> >> on and tracking - during a frontal attack. Now, A B70 at M3.0 and
>> >> +75000 would be like a giant IR beacon with a radar signature like the
>> >> Vertical Assembly Building, all screaming 'Shoot Me'.
>> >
>> >The only problem with high-speed IR missiles over long ranges is that
>> >the window in the front of the seeker head gets hot enough to blind the
>> >warhead.
>>
>> The AIM-47 Falcon had something like a hundred mile range and flew at
>> Mach 6. It had IR terminal guidance. Today's THAAD uses IR also
>> (several others do but they use kill vehicles that are protected
>> before the leave the atmosphere). HEDI also used an IR terminal
>> guidance. Think of HEDI as a hit-to-kill Sprint missile. I don't
>> know if they ever did get the IR seeker to work though. ISTR it was
>> cooled by nitrogen gas flowing over the outside of the seeker and used
>> a synthetic sapphire window.
>
>Yeah, you have to do some serious redesign to make IR a good high-speed
>targeting method. It's just easier to do it the other way around for
>the sort of target we're looking at - superfast, very high.
>
>The AIM-47 never really worked that well,


You might want to read up on the test shots. Even today they are some
of the most impressive out there and they were like six for seven on
hits and some of them were direct hits. Not to mention all of them
were shooting down :-) with one of them smacking a target at 1500
feet from something lik 75 to 80,000 ft.

[Scott Ferrin]

On Sat, 20 Dec 2003 15:19:54 -0600, BOB URZ
> wrote:

>
>
>Scott Ferrin wrote:
>
>> >You could make a case for a Sam being able to knock out any airplane. So why
>> >build any at all?
>> >
>> >Assuming B70's were built and upgraded umpteen times by now,
>> >what do you think the results would be with a re-engine of the six pack with a
>> >modern supercruise engine such as a F119?
>> >
>> >Bob
>>
>> Actually I'd be surprised if the F119 powered one wasn't *slower*.
>> The J93 was designed for Mach 3 and high altitudes. The F119 is not.
>
>I realize that airflow and inlet geometry are critical for a high
>mach plane, but what would be different in the guts of the engine?
>Did the XB-70 burn a non standard fuel like the SR71?

It didn't use special fuel (although they wanted to use a fuel with
boron added at one point). I *think* part of the reason for the
differences would be related to the compression ratio of the engines
and that they were straight turbojets rather than turbofans. The
XB-70, Blackbirds, and Mig-25 all used low pressure engines I *think*
because at high speed they compressed the air so much to get something
to work with that by the time it got to the engines they couldn't take
the temperature of compressing a ton more. ISTR the J93's compression
ratio being around 9 to 1 whereas something like the F100-129 is up
around 32-1 or 36-1. Then again they though the could get the
Crusader III up to 2.9 with a J75 so who knows. All of this is just
my opinion from what I've read over the years so hopefully someone
will weigh in who knows a lot about it.

[Felger Carbon]

"BOB URZ" > wrote in message
...
>
>
> Scott Ferrin wrote:
>
> > >Assuming B70's were built and upgraded umpteen times by now,
> > >what do you think the results would be with a re-engine of the
six pack with a
> > >modern supercruise engine such as a F119?
> > >
> > >Bob
> >
> > Actually I'd be surprised if the F119 powered one wasn't *slower*.
> > The J93 was designed for Mach 3 and high altitudes. The F119 is
not.
>
> I realize that airflow and inlet geometry are critical for a high
> mach plane, but what would be different in the guts of the engine?
> Did the XB-70 burn a non standard fuel like the SR71?

Hey, it's Xmas. Mebbe I can make another mistake.

For a supersonic aircraft, the purpose of the inlet geometry is to
reduce the supersonic airflow at atmospheric pressure to subsonic
airflow at super-atmospheric pressure. ;-)

This means there's more oxygen to burn more fuel, thus getting more
power. It also runs the engine hotter. The faster the supersonic
aircraft goes, the hotter the engine can run.

This raises the following critical question: how long an engine life
do you want? I understand the Mig-31 Foxhound is _capable_ of
astonishingly high speeds, as it has demonstrated on at least one
occasion in the mideast. It generally doesn't, because an immediate
engine overhaul/replacement is then needed.

The F-119 engined F-22 has fixed inlets and is not especially fast.
The engine, therefore, does _not_ have to be made of the *very*
expensive highest-temperature alloys. My question is, how long would
the F-119 last in a mach3 aircraft like the B-70?

[Scott Ferrin]

>The F-119 engined F-22 has fixed inlets and is not especially fast.

What makes you think fixed inlets make a difference?


>The engine, therefore, does _not_ have to be made of the *very*
>expensive highest-temperature alloys.


The F119 is made of MUCH better alloys than the J93. I think the
temperature problem is handled by the fact that the J93 compresses the
air much less than an F119. So does the J58 and the engine the Mig-25
uses.


> My question is, how long would
>the F-119 last in a mach3 aircraft like the B-70?
>

[Felger Carbon]

"Scott Ferrin" > wrote in message
...
>
> >The F-119 engined F-22 has fixed inlets and is not especially fast.
>
> What makes you think fixed inlets make a difference?

At high mach, the air bounces several successive shock waves off the
inlet, in the process of dropping the airspeed and increasing the air
pressure.

Airplanes such as the F4 Phantom, the Tomcat, F-15, Mig-25 and Mig-31
(among others) have variable inlets specifically so the inlet can be
tuned to the speed for most efficient operation. The SR-71 had a
spike arrangement in front of the engine that performed as a variable
inlet.

Airplanes such as the F-16 and F-22 use fixed inlets, and have lower
top speeds (according to Janes). Fixed inlets are used either to
reduce costs, or (in the case of the F-22) to improve stealth
caracteristics. Variable inlets aren't very stealthy.

[Scott Ferrin]

On Sun, 21 Dec 2003 22:39:43 GMT, "Felger Carbon" >
wrote:

>"Scott Ferrin" > wrote in message
...
>>
>> >The F-119 engined F-22 has fixed inlets and is not especially fast.
>>
>> What makes you think fixed inlets make a difference?
>
>At high mach, the air bounces several successive shock waves off the
>inlet, in the process of dropping the airspeed and increasing the air
>pressure.
>
>Airplanes such as the F4 Phantom, the Tomcat, F-15, Mig-25 and Mig-31
>(among others) have variable inlets specifically so the inlet can be
>tuned to the speed for most efficient operation. The SR-71 had a
>spike arrangement in front of the engine that performed as a variable
>inlet.
>
>Airplanes such as the F-16 and F-22 use fixed inlets, and have lower
>top speeds (according to Janes). Fixed inlets are used either to
>reduce costs, or (in the case of the F-22) to improve stealth
>caracteristics. Variable inlets aren't very stealthy.
>


Fixed inlets have been discussed to death here. Basically it comes
down to the speed they were designed for. A fixed inlet can be
optimized for high speed.

[Felger Carbon]

"Scott Ferrin" > wrote in message
...
>
> Fixed inlets have been discussed to death here. Basically it comes
> down to the speed they were designed for. A fixed inlet can be
> optimized for high speed.

Since variable inlets are not needed for any purpose, why do so many
jet fighters use them? To give the maintenance monkeys something
further to do?

Why, according to Janes', does the ancient-history F-4 have a higher
top speed than the future-generation F-22?

[Paul F Austin]

"Felger Carbon" wrote
> "Scott Ferrin" wrote
> >
> > Fixed inlets have been discussed to death here. Basically it comes
> > down to the speed they were designed for. A fixed inlet can be
> > optimized for high speed.
>
> Since variable inlets are not needed for any purpose, why do so many
> jet fighters use them? To give the maintenance monkeys something
> further to do?
>
> Why, according to Janes', does the ancient-history F-4 have a higher
> top speed than the future-generation F-22?

The main reason is that Janes' doesn't know. And neither do we.

There's a consensous in the US that very high mach numbers have little
military utility. For all US fighters prior to the F-22, persistence at the
placard Mach number could be measured in (few) minutes. Operations research
from the Vietnam War showed (IIRC) that the number of combat minutes spent
at Mach numbers from 1.0 to 1.2 in the whole war were fewer than about 15
and_no_combat time was logged at Mach numbers over about M1.5. Movable
inlets like the F-4s dominated propulsion maintenance workload and so were
not judged to be worthwhile.

The F-22 designers were told that reduced signatures counted for_lots_more
than did maximum Mach number in afterburner. Maximum Mach number in mil-
power was also counted more heavily than AB Mach number. So the F-119 was
sized with enough airflow to meet the performance requirements in "dry"
operation and the inlet was tuned to operate efficiently in the speed range
from M1 to M2. Any performance above that level is fortuitous but wasn't
required. I suspect that if the designers could trade all performance above
M2 for greater persistence at M1.5, they would.

[Tex Houston]

"Felger Carbon" > wrote in message
k.net...
> "Scott Ferrin" > wrote in message
> ...
> >
> > Fixed inlets have been discussed to death here. Basically it comes
> > down to the speed they were designed for. A fixed inlet can be
> > optimized for high speed.
>
> Since variable inlets are not needed for any purpose, why do so many
> jet fighters use them? To give the maintenance monkeys something
> further to do?
>
> Why, according to Janes', does the ancient-history F-4 have a higher
> top speed than the future-generation F-22?


Maintenance monkeys??? Even I as an Ops type have a great respect for great
job maintenance MEN and WOMEN do under often difficult circumstances and
always long hours. I find your phrase highly insulting.

****ed,

Tex Houston

[Chad Irby]

In article >,
"Felger Carbon" > wrote:

> "Scott Ferrin" > wrote in message
> ...
> >
> > Fixed inlets have been discussed to death here. Basically it comes
> > down to the speed they were designed for. A fixed inlet can be
> > optimized for high speed.
>
> Since variable inlets are not needed for any purpose, why do so many
> jet fighters use them? To give the maintenance monkeys something
> further to do?

It's not that they're "not needed," they're just one way of dealing with
the problem, that a lot of jets have used. The simplest for most uses.

On the other hand, if you optimize a fixed inlet for high speed, it's
costs you in the low speed regimes.

> Why, according to Janes', does the ancient-history F-4 have a higher
> top speed than the future-generation F-22?

Part of that is what the USAF is announcing. They only say "Mach 2,"
and everyone else gets to guess what the top speed is.

--
cirby at cfl.rr.com

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

[B2431]

>From: "Felger Carbon"
>Date: 12/21/2003 6:33 PM Central Standard Time
>Message-id: >
>
>"Scott Ferrin" > wrote in message
...
>>
>> Fixed inlets have been discussed to death here. Basically it comes
>> down to the speed they were designed for. A fixed inlet can be
>> optimized for high speed.
>
>Since variable inlets are not needed for any purpose, why do so many
>jet fighters use them?

You misunderstood. A fixed inlet can be selected for a given speed. It is less
efficient above and below that speed.

Dan, U.S. Air Force, retired

[Felger Carbon]

"Tex Houston" > wrote in message
...
>
> Maintenance monkeys??? Even I as an Ops type have a great respect
for great
> job maintenance MEN and WOMEN do under often difficult circumstances
and
> always long hours. I find your phrase highly insulting.

I spent 4 years in the Air Force. 2.5 of those years I served at
Nouasseur AFB, just southeast of Casablanca, Morocco as a maintenance
monkey. My specialty was radio communications and navigation.
Nouasseur was a MATS base; I worked on C-124s and C-121s and the
like. This was Jan 1956 to Aug 1958. When I arrived in Morocco it
was still French Morocco, but it got it's independence a very few
months later.

[Felger Carbon]

"B2431" > wrote in message
...
> >From: "Felger Carbon"
> >Date: 12/21/2003 6:33 PM Central Standard Time
> >Message-id: >
> >
> >"Scott Ferrin" > wrote in message
> ...
> >>
> >> Fixed inlets have been discussed to death here. Basically it
comes
> >> down to the speed they were designed for. A fixed inlet can be
> >> optimized for high speed.
> >
> >Since variable inlets are not needed for any purpose, why do so
many
> >jet fighters use them?
>
> You misunderstood. A fixed inlet can be selected for a given speed.
It is less
> efficient above and below that speed.
>
> Dan, U.S. Air Force, retired

Dan, thank you for making exactly the point I thought I was making!
If you want an optimized inlet for whatever supersonic speed you're
at, the inlet must be variable. That's why so many US and Soviet
aircraft in fact have variable inlets.

[Tex Houston]

"Felger Carbon" > wrote in message
k.net...
> "Tex Houston" > wrote in message
> ...
> >
> > Maintenance monkeys??? Even I as an Ops type have a great respect
> for great
> > job maintenance MEN and WOMEN do under often difficult circumstances
> and
> > always long hours. I find your phrase highly insulting.
>
> I spent 4 years in the Air Force. 2.5 of those years I served at
> Nouasseur AFB, just southeast of Casablanca, Morocco as a maintenance
> monkey. My specialty was radio communications and navigation.
> Nouasseur was a MATS base; I worked on C-124s and C-121s and the
> like. This was Jan 1956 to Aug 1958. When I arrived in Morocco it
> was still French Morocco, but it got it's independence a very few
> months later.

I was in during those years and a lot more. You may take delight in the use
of a denigrating phrase for maintenance personnel. I do not. I know too
many of those fine people who came through for me when I had to ask the
impossible of them.

Tex Houston

[Felger Carbon]

"Tex Houston" > wrote in message
...
>
> "Felger Carbon" > wrote in message
> k.net...
> > "Tex Houston" > wrote in message
> > ...
> > >
> > > Maintenance monkeys??? Even I as an Ops type have a great
respect
> > for great
> > > job maintenance MEN and WOMEN do under often difficult
circumstances
> > and
> > > always long hours. I find your phrase highly insulting.
> >
> > I spent 4 years in the Air Force. 2.5 of those years I served at
> > Nouasseur AFB, just southeast of Casablanca, Morocco as a
maintenance
> > monkey. My specialty was radio communications and navigation.
> > Nouasseur was a MATS base; I worked on C-124s and C-121s and the
> > like. This was Jan 1956 to Aug 1958. When I arrived in Morocco
it
> > was still French Morocco, but it got it's independence a very few
> > months later.
>
> I was in during those years and a lot more. You may take delight in
the use
> of a denigrating phrase for maintenance personnel. I do not. I
know too
> many of those fine people who came through for me when I had to ask
the
> impossible of them.

Tex, I did not intend derogation. The term "monkey" would be easily
understood by anyone who has scrambled up as many ladders (to the
cockpit) and down as many ladders (to the electronics equipment bay)
in a C-124 Globemaster as I have. Oh, yes: and the ladder from the
ground into the bird's cargo compartment.

BTW, Nouasseur was not a hardship base; the standard tour was 18
months. The reason I was there 30 months was that I voluntarily
extended for a year. Her name was Arlette. ;-)

[Peter Stickney]

In article >,
BOB URZ > writes:
>
>
> Scott Ferrin wrote:
>
>> >You could make a case for a Sam being able to knock out any airplane. So why
>> >build any at all?
>> >
>> >Assuming B70's were built and upgraded umpteen times by now,
>> >what do you think the results would be with a re-engine of the six pack with a
>> >modern supercruise engine such as a F119?
>> >
>> >Bob
>>
>> Actually I'd be surprised if the F119 powered one wasn't *slower*.
>> The J93 was designed for Mach 3 and high altitudes. The F119 is not.
>
> I realize that airflow and inlet geometry are critical for a high
> mach plane, but what would be different in the guts of the engine?
> Did the XB-70 burn a non standard fuel like the SR71?
(I'll over-simplify a bit here - its too late to throw numbers around.)
The biggest issue is the pressure ratio of the compressor. Basically,
there's 2 ways to get a lot of thrust out of a jet engine. You can
compress a lot of air moderately, or a smaller amount of air a lot.
Then you add heat up to the point that the materiels in the turbine
section can still pretty much hang together, and take soem of that
energy out as you turn the turbine/compressor comination.
Then, if you really want to go fast, you add more heat, until you
either can't pump fuel in any faster, or the tailpipe starts to melt.

Engines with higher compression ratios tend to be more fuel efficient.
The problem is, when you're compressing the air, you're heating it
up. The more you compress, the hotter it gets. If the engine's not
moving, it's no big deal. But as the engine is moving, the inlets
supply air compressed by ramming the air into the inlets. The faster
you go, teh more compressed, and hotter, it gets. When the
compressed, hot air comes out of the compressor, into the combustors,
it's then really hot. With a highpressure ratio compressor, that
means that you can't burn much fuel before you'll exceed the turbine's
temperature limits, and you may even exceed the working temperature of
the compressor. A low pressure ratio engine is less efficent by
itself, but at high speeds, taken in combination with the inlet
system, it's more efficient, and develops more thrust. Oh, yeah, one
more thing - as the turbine drives the compressor, it extracts energy
from the hot gas. The higher the compression, the more energy gets
extracted. A lower pressure engine at high speed has more heat energy
after the turbine, going into teh tailpipe, and so requires less fuel
to be added by the afterburner to reach its maximum temperature.
High pressure engens tend to be most efficient around Mach 0.9, and
low pressure engine are most efficient at a much higher speed -
typically in the range of Mach 1.5 or so. The speed at which you
start losing thrust becasue you can't burn enough fuel in the
combustors is also higher. A high pressure engine is still much more
efficent at its best speed, however. With the afterburner operating,
the thrust curves look about the same, increasing as airspeed
increases until the pumps can't feed any more fuel. So - Military
Power cruise speeds will be higher for the low pressure engine, but
the dash speed would be the same no matter what. (Modulo materials
limits in the compressor - the J79 in the F-104 or F-4 is limited to a
maximum Ram Temperature or 100 deg C at the compressor face - that
usually occurs somewhere around Mach 2 at altitude).

Basically, in the 1950s, when the B-70 was being designed, the ideal
high supersonic engine was to have been a large, single-spool turbojet
with a compression ration of about 7-9:1, and a Mass Flow of around
300#(mass)/sec. That pretty much suns up the J93, the DH Gyron, the
Orenda Iroquis, and the MiG-25's powerplants. The greater thrust
from the main gas generator means tht you don't have to be dumping as
much fuel into the Afterburner, so supersonic endurance and range are
improved. Note that the ultimate expression of a supersonic het
engine is the Ramjet, where the whole turbojet section is viewed as a
liability and is chicked out, leaving just an inlet and an
afterburner.

If you're going to build an airplane that will actually be spending
most of its time cruising around Mach 0.9, but you want to have a high
dash speed for short periods, you're much better off going with a high
pressure engine.

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

[Scott Ferrin]

>> You misunderstood. A fixed inlet can be selected for a given speed.
>It is less
>> efficient above and below that speed.
>>
>> Dan, U.S. Air Force, retired
>
>Dan, thank you for making exactly the point I thought I was making!
>If you want an optimized inlet for whatever supersonic speed you're
>at, the inlet must be variable. That's why so many US and Soviet
>aircraft in fact have variable inlets.


If you do a dejanews search you can find where this has been beat to
death adnausium. In a nutshell optimizing for Mach 1.8 is not going
to be hugely different than 2.2. Optimizing for 0.9 is going to be
very different than 1.7 or 1.8. It wouldn't surprise me at all if the
F-22's inlet is less effiecient than an F-16's at subsonic speeds. On
the other hand is optimizing for subsonic speed and making the intake
able to handle supersonic speed the same as optimizing for supersonic
speed and making the intake able to deal with the lower speeds? Just
about any aircraft is going to be going subsonic 95% of the time so
you'd want to do the former. An aircraft that is going to spend a
significant amount of time above the speed of sound is going to use
the latter. Just about every ramjet out there has a fixed inlet that
is optimized for supersonic speed because it's not going to spend much
time subsonic. Two aircraft come to mind that could go quite a bit
faster than Mach 2 that have fixed inlets. The F8U-3 Crusader and the
F-22. ASALM went Mach 5.4 with a fixed inlet. Boeing's ATF
contender actually had the variable geometry apperatus way down the
pipe so you couldn't see it from the outside. I'm not implying the
F-22 has this, I am simply saying that you can't judge an aircraft's
speed capability strictly by whether it has a variable geometry
intake.

[Dweezil Dwarftosser]

Tex Houston wrote:
>
> "Felger Carbon" > wrote in message
> k.net...
> > "Tex Houston" > wrote in message
> > ...
> > >
> > > Maintenance monkeys??? Even I as an Ops type have a great respect
> > for great
> > > job maintenance MEN and WOMEN do under often difficult circumstances
> > and
> > > always long hours. I find your phrase highly insulting.
> >
> > I spent 4 years in the Air Force. 2.5 of those years I served at
> > Nouasseur AFB, just southeast of Casablanca, Morocco as a maintenance
> > monkey. My specialty was radio communications and navigation.
> > Nouasseur was a MATS base; I worked on C-124s and C-121s and the
> > like. This was Jan 1956 to Aug 1958. When I arrived in Morocco it
> > was still French Morocco, but it got it's independence a very few
> > months later.
>
> I was in during those years and a lot more. You may take delight in the use
> of a denigrating phrase for maintenance personnel. I do not. I know too
> many of those fine people who came through for me when I had to ask the
> impossible of them.

Like the "N" word, it really matters only when the
person making the statement is/was NOT part the
group.

Us enlisted swine knew full well that without us to
watch out for the flight suit inserts, you would
soon be reduced to having one hand follow the other
at the Stag Bar, retelling your tale of heroism (when
you got an entire flying hour entered into your log
book last month).

;-)

John T. former F-4 WCS toad.

[Tex Houston]

"Dweezil Dwarftosser" > wrote in message
...
> Tex Houston wrote:
> Us enlisted swine knew full well that without us to
> watch out for the flight suit inserts, you would
> soon be reduced to having one hand follow the other
> at the Stag Bar, retelling your tale of heroism (when
> you got an entire flying hour entered into your log
> book last month).
>
> ;-)
>
> John T. former F-4 WCS toad.

Whatever gave you the idea I wore a flight suit or had a commission?

Tex Houston

[Alan Minyard]

On Sun, 21 Dec 2003 20:23:31 -0700, "Tex Houston" > wrote:

>
>"Felger Carbon" > wrote in message
k.net...
>> "Tex Houston" > wrote in message
>> ...
>> >
>> > Maintenance monkeys??? Even I as an Ops type have a great respect
>> for great
>> > job maintenance MEN and WOMEN do under often difficult circumstances
>> and
>> > always long hours. I find your phrase highly insulting.
>>
>> I spent 4 years in the Air Force. 2.5 of those years I served at
>> Nouasseur AFB, just southeast of Casablanca, Morocco as a maintenance
>> monkey. My specialty was radio communications and navigation.
>> Nouasseur was a MATS base; I worked on C-124s and C-121s and the
>> like. This was Jan 1956 to Aug 1958. When I arrived in Morocco it
>> was still French Morocco, but it got it's independence a very few
>> months later.
>
>I was in during those years and a lot more. You may take delight in the use
>of a denigrating phrase for maintenance personnel. I do not. I know too
>many of those fine people who came through for me when I had to ask the
>impossible of them.
>
>Tex Houston
>
>
Tex, no offense, but I believe that those fine people "came through" for
the United States, the USAF, and (perhaps) the squadron.

Al Minyard

[Scott Ferrin]

On Sun, 21 Dec 2003 20:23:31 -0700, "Tex Houston"
> wrote:

>
>"Felger Carbon" > wrote in message
k.net...
>> "Tex Houston" > wrote in message
>> ...
>> >
>> > Maintenance monkeys??? Even I as an Ops type have a great respect
>> for great
>> > job maintenance MEN and WOMEN do under often difficult circumstances
>> and
>> > always long hours. I find your phrase highly insulting.
>>
>> I spent 4 years in the Air Force. 2.5 of those years I served at
>> Nouasseur AFB, just southeast of Casablanca, Morocco as a maintenance
>> monkey. My specialty was radio communications and navigation.
>> Nouasseur was a MATS base; I worked on C-124s and C-121s and the
>> like. This was Jan 1956 to Aug 1958. When I arrived in Morocco it
>> was still French Morocco, but it got it's independence a very few
>> months later.
>
>I was in during those years and a lot more. You may take delight in the use
>of a denigrating phrase for maintenance personnel. I do not. I know too
>many of those fine people who came through for me when I had to ask the
>impossible of them.
>
>Tex Houston

Uhm. . .as he said *he* was a "maintanance monkey" I don't think he
meant it in a derogetory way.

[Felger Carbon]

"Peter Stickney" > wrote in message
...
> >>
> >> Actually I'd be surprised if the F119 powered one wasn't
*slower*.
> >> The J93 was designed for Mach 3 and high altitudes. The F119 is
not.
>
> Engines with higher compression ratios tend to be more fuel
efficient.
> The problem is, when you're compressing the air, you're heating it
> up. The more you compress, the hotter it gets. If the engine's not
> moving, it's no big deal. But as the engine is moving, the inlets
> supply air compressed by ramming the air into the inlets. The
faster
> you go, teh more compressed, and hotter, it gets. When the
> compressed, hot air comes out of the compressor, into the
combustors,
> it's then really hot. With a highpressure ratio compressor, that
> means that you can't burn much fuel before you'll exceed the
turbine's
> temperature limits, and you may even exceed the working temperature
of
> the compressor.

Thank you, Peter. Excellent support for my original posting on this
thread, which was that the F-119 engine would probably not be optimum
for the mach 3 B-70 because of engine overheating. You said it much
better than I did.

[Matthew G. Saroff]

Scott Ferrin > wrote:

>It didn't use special fuel (although they wanted to use a fuel with
>boron added at one point). I *think* part of the reason for the
>differences would be related to the compression ratio of the engines
>and that they were straight turbojets rather than turbofans. The
>XB-70, Blackbirds, and Mig-25 all used low pressure engines I *think*
>because at high speed they compressed the air so much to get something
>to work with that by the time it got to the engines they couldn't take
>the temperature of compressing a ton more. ISTR the J93's compression
>ratio being around 9 to 1 whereas something like the F100-129 is up
>around 32-1 or 36-1. Then again they though the could get the
>Crusader III up to 2.9 with a J75 so who knows. All of this is just
>my opinion from what I've read over the years so hopefully someone
>will weigh in who knows a lot about it.

IIRC, the XB-70 engine had bypass ducting similar to the
engines on the SR-71.
--
--Matthew Saroff

I'm not an actor, but I play one on TV.
Check http://www.pobox.com/~msaroff, including The Bad Hair Web Page

[Matthew G. Saroff]

"Felger Carbon" > wrote:

>
>Dan, thank you for making exactly the point I thought I was making!
>If you want an optimized inlet for whatever supersonic speed you're
>at, the inlet must be variable. That's why so many US and Soviet
>aircraft in fact have variable inlets.
>
With the proviso that a fixed inlet optimized for very
high speeds may never be able to get there, as efficiency might
be too low at off design speeds.

The Blackbird has some of this problems with its inlets,
where they were not particularly efficient in the trans sonic
regime, and it accelerated slowly there.
--
--Matthew Saroff

I'm not an actor, but I play one on TV.
Check http://www.pobox.com/~msaroff, including The Bad Hair Web Page

[sid]

Matthew G. Saroff > wrote in message >...
>
> The Blackbird has some of this problems with its inlets,
> where they were not particularly efficient in the trans sonic
> regime, and it accelerated slowly there.

You have to give credit to the North American engineers who came up
with the basic inlet shape that they used on their mach plus designs
starting with the F-107 through the A3J and XB-70. Its been one of the
most enduring shapes on supersonic aircraft since. Look at the inlet
shape of the Concorde, Soviet fighters, and the F/A-18E and you will
see the resemblance. I wonder who the slide rule slingin' unsung hero
was at NA who first thought it up.
http://www.shanaberger.com/images/F-107.jpg
http://aviaweb.calexo.org/monographies/vigilante/img/ya3j-1.jpg
http://www.123.cl/canales/noticias/img/concorde.gif
http://www.armscontrol.ru/atmtc/Arms_systems/Avia/Russia/Su27/su-37.jpg
http://www.flug-revue.rotor.com/FRTypen/FRfotmil/F-18EUn.JPG