XB-70 vs B-2

"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 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. ;-)

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

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.

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.

"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

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


"Felger Carbon" wrote in message
nk.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

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


"Felger Carbon" wrote in message
nk.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.

"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.

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