max altitude and Mach 1

In article ,
"John Carrier" writes:
You've asked a Short Question with a Long Answer, I'm afraid.

Peter, why do I suspect that when asked the time, you tell the inquirer how
to build a watch?

Evaluating airplane performance, especially from the stuff published
in the Popular Press, is a tricky business.

Big snip.

In the mid '60s, wanting a higher performance Interceptor for Southern
Florida, the USAF re-engined some of the F-104As with the J79-19
engine used on late model Phantoms. This had a non-afterburning
Static Thrust of 11,900#, and an Afterburning Static Thrust of
17,900#. With that much power, the 750 KEAS airspeed limit was
reached at all altitudes, from Sea Level on up, and the 250 Degree F
limit was reached from 20,000' to the maximum ceiling of around
66,000'. The ceiling continuously increased from 51,00' at Mach o.9
to 66,000' at Mach 2.0. It could very easily have flown higher and
faster, if the airframe limits were ignored.

Nice try, but untrue. The 750 airframe limit was not a factor above about
40,000 feet ... it was not reached at "all altitudes." (BTW, airframe limit
IS a factor ... was? ... for the SR-71 at intermediate altitudes.) Inlet
temperature could be an issue at the extreme top end ... Skyburner F-4 had
and Greenameyer's F-104 was to have inlet water injection ... but we're
talking 2.5 plus here.

John, where did I say that it was? Ah, never mind, I see where I
didn't state it clearly. Sorry about that. I thought I'd mentioned
that the F-104 flight limits were 750 KEAS or 250 Def F at teh
compressor face, whichever came first. In the case of the -19
powered F-104A, it would run out to the 750 KEAS limit from Sea Level
on up, and the 250 Deg F limit would be reached at anout 20,000', at
about Mach 1.70. Obviously, you'd hold to whichever limit came
first. From 20 Kft on up, the limit you'd run into first was the 250
Deg F limit. At 35,000', the 250 Drg F limit is about 650 KEAS. At
40,000', it's about 550 KEAS. at 50 Kft, it's about 450 KEAS. (BTW,
the SR-71's Q (EAS) limit is fairly low, something like about 450
KEAS.)

Sure- above the Tropopause, the temperature remains constant. and the
250 Deg F limit is reached at about Mach 2.0. If you've got a way to
cool the inlet air as it's being compressed, such as the
Pre-Compressor Cooling on the Skyburner F4H (Pre 1962, after all), or
the similar Water Injection system that Darryl Greenameyer was going
to use, then you can run out to a higher speed safely.


As to "very easily flown higher and faster" the J-79 would experience burner
blow out between 65-70,000 feet and the engines would have to be shut down
approaching 75,000 because their minimum fuel flow settings would be too
high and cause overtemp. (Greenameyer intended to modify the fuel control
and use specially formulated fuel to allow the engine to run longer until
shutdown required in his zoom climb.)

That would be higher and faster at the same time - One very
interesting bit from the F-104A (-19) engine's SAC Chart, Jun 1970,
(If you need to see it, I'll be glad to E-mail you a copy)
Is that the ceiling is increasing as it approaches Mach 2,0/66,000'.
That's about 320 KEAS. As far as the engine is concerned, it's
being delivered 320 Kt/Sea Level conditions from teh inlet. They sure seem
to run O.K. in that range. Of course, if you're slower, it'll be a
_lot_ different. But that's the point - With the -19 engines F-104A,
it had the power to go a lot faster than its flight limits would
allow. So it had the potential to, if you were ignoring the limits,
deliver some astounding performance.

There didn't seem to be that much problem with a J79 above 60 Kft -
the B-58 on a high altitude bomb run at Mach 2.0 would be over the
target at 64,000'.

The Rutkowski trajectory for the F-4 and F-104 zoom climbs is fairly
similar - Take off, Accelerate to Mach 0.9, climb at Mach 0.9 t0 a bit
above 36,000' (The Tropopause, where the margin of Thrust over Drag will be
greates, enter a slight descent to get through the transonic drag rise
quickly, accelerate out at 36,000' to however fast you can go, then a
2G pull to straight up and maintain 90 degrees nose high. The
airplane will be decelerateing from that point on, and at 60-70,000'
will be flying at a rather low EAS - somewhere arount 100 KT EAS
wouldn't be too out of line.


To simplify your response, most older designs had high mach as a primary
design goal and thrust/drag created large PsubS "bubbles" past the transonic
drag rise region (F-104 a prime example, original F-14B ... glove vanes and
inlet scheduling intact ... another). That excess power in the 1.4-1.6
region (usually, SR-71 was much higher) allowed higher service ceilings
while supersonic.

That's true - Speed was everything in the '50s, and they found that
with proper inlet design, they could maintain a sufficient thrust
margin to get the airplane up to some big mach number. Let's not
forget too, that Ps is Specefic Excess Acceleration * True Airspeed,
either - the faster you're going, the less excess thrust you'll need
for a given Rate of Climb.

Current design emphasis is on subsonic performance with high Q (indicated
airspeed) but not usually high mach as a bonus of their high thrust/weight
ratios. No large PsubS gains once above transonic drag rise. Ergo no
improvement in service ceiling supersonic.

Right.

Thanks for pointing out my poor wording, above - It seems that we were
talking about the same thing, I just expressed it poorly.

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