? for the F-4B pilots

"J" wrote in
news

"Peter Stickney" wrote in message
om...
"J" wrote in message
. rr.com...
"Peter Stickney" wrote in message
I'm going to be simplifying a bit, for those who don't like
Thermodynamics.
I know you are trying, but don't give up your day job. :-) There
are
some
problems and misconceptions with your simple explanation on how and
why
it
works.

One of the dangers that comes from playing to the audience, RR.
I'd rather run the risk of over-simplicating for those who aren't
technically inclined, vs. drowning them with a firehose of Tech
Stuff. (Think of it as bait - we'll suck 'em in, get 'em hooked,
and then gaff 'em with the numbers.)

Why turn 'em off with a lot of True Stuff about Turbine Stresses,
Mass Flow, Pressure Ratios, Fuel/Air ratios, Compressor & Turbine
Efficiencies & suchlike, if it only makes their eyes glaze over?

(Oh, and as for an afterburning turbojet being considered 2 separate
engines, there have been engine installations that did just that.
The powerplant for the Republic XF-103 Mach 4 interceptor. (Cancelled
in the late '50s, but they'd cut metal for it, and the powerplant
had been tested at the N.A.C.A. tunnels and the tunnels at (I think)
Tullahoma. Basically, it was a Wright J67 (Bristol Olympus "fixed"
by Curtiss-Wright, just like they did to the Sapphire to get the J65,
with a big afterburner spaced way back in the tail. At low speeds,
it was pretty much a normal gas generator/AB combination, but as
speed picked up, and the gas generator output started decreasing,
somewhere around Mach 2, they'd divert the inlet flow around the
turbojet, shut the turbojet down, and keep going on just the AB,
using it as a ramjet.) It's just crazy enough to work.

--
Pete Stickney

Whoooooo! Don't include me in your post. I don't agree with you at
all. You are throwing a bunch of big words in there like you know what
you are talking about, which I don't think you do at all. Your
statement of

"If you like, you can think of an afterburning turbojet as two
engines: The turbojet itself, and a ramjet downstream."

Is a crock. And the J-67 was a different concept. Enough said!

"PLONK"

Red Rider

Well, Red, he got it pretty close to right on the XF-103.

From http://home.att.net/~jbaugher1/f103.html
*****
Specifications of the XF-103:
Engines: One Wright XJ67-W-3 turbojet, rated at 15,000 lb.st. dry and
22,000 lb.s.t. with afterburning, plus one XRJ55-W-1 ramjet rated at
18,800 pounds of thrust. and

This phenomenal performance was to be achieved by the adoption of a dual-
cycle propulsion system. Takeoff and normal cruise were to be powered by
a Wright XJ67-W-3 turbojet, rated at 15,000 lb.s.t. dry and 22,000
lb.s.t. with afterburning. The XJ67 was a license-built version of the
Bristol Olympus. At high speed, the thrust of the turbojet was to be
augmented by a XRJ55-W-1 ramjet, capable of delivering 18,800 pounds of
thrust. With both powerplants operating, a total thrust of 37,000 pounds
could be achieved at altitude.
*****

From http://www.fas.org/nuke/guide/usa/airdef/f-103.htm
*****
The Republic XF-103 Model AP-57 had a Delta wing swept-back 55 degrees at
the leading edge and incorporates a variable incidence feature. The
horizontal tail is of the Delta configuration with a sweep-back angle of
60 degrees at the leading edge. The alighting gear was of the tricycle
type and retracts into the fuselage. The turbo-jet was a Wright
Aeronautical Corporation XJ-67-W-1 power plant with afterburner. A Ferri
type two-dimensional engine air inlet is used. The thrust of the turbo-
jet engine was limited at high Mach numbers by the allowable turbine
inlet temperature. The air bypassed the engine compressor and turbine,
and using the afterburner as a ram-jet combustion chamber, the available
thrust is greatly increased above a Mach number of 2.0
*****

As for the concept "you can think of an afterburning turbojet as two
engines: The turbojet itself, and a ramjet downstream.", if you think
about it, that's exactly how it works - feed the exhaust of the jet with
more fuel, light it and get thrust, no different than a ramjet. The force
of the incoming air keeps the flame front from blowing forward.

Regarding the remainder of his explanation, where are all the big words?
Seems like a pretty reasonable explanation of the basic operating
principles. All engines are basically air pumps; more air throughput,
more power.

Dave in San Diego

--
-
"For once you have tasted flight, you will walk the earth with your eyes
turned skyward;
For there you have been, and there you long to return."
Leonardo da Vinci