XB-70 vs B-2

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?

"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.

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.

"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?

"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.

"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

In article t,
"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.

From: "Felger Carbon"
Date: 12/21/2003 6:33 PM Central Standard Time
Message-id: t

"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

"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.

"B2431" wrote in message
...
From: "Felger Carbon"
Date: 12/21/2003 6:33 PM Central Standard Time
Message-id: t

"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.