"Trevor Jones" wrote in message
...
Harold & Susan Vordos wrote:

A ram jet uses the shock wave fron the inlet air as a barrier to the
flame front
moving too far forward.

Not correct. Ram jets have flame holders (as do turbojet afterburners) to
keep the flame from moving forward -- and typically, the flame problem is
that it tends to move backwards -- it's called "blowing out". That's not
at all the way a ramjet works. A ramjet has a compressor -- it is called
the inlet. It is a converging-diverging nozzle. In supersonic airflow, the
mach number and air velocity DECREASES when going through a converging
nozzle (conversely, its speed increases through a diverging nozzle -- just
the opposite of subsonic flow. As the air velocity decreases, the air
pressure necessarily increases -- hence the compression. In an ideal
inlet, the mach number at the inlet throat is 1.00 so that the transition
from supersonic to subsonic flow is very gentle and the compression is the
most efficient it can possibly be. Generally, it is nigh impossible to get
the shock wave to stay at that ideal point and it is allowed to occur at
some higher mach number, such as 1.4 and forward of the throat -- Ramjets,
despite their superficial simplicity are very ticklish and tender beasts.
There's there the problem of getting it up to a speed where the compression
is adequate to run the engine. Then there's the problem that at subsonic
speeds, the inlet works the wrong way for supersonic speeds -- so geometry
and things must be adjusted as the jet speeds up. Practically speaking,
there aren't any realistic subsonic ramjets -- and no supersonic ramjet has
made it into serial production either. Nasty little beasties. You'd never
think an empty pipe (except for the flame holders, throat geometry, exhaust
nozzle geometry, etc.) would be so complicated.


No forward speed = no run at all.

That's correct. And hardly that below mach 1.

Boris

Who in his mispent youth got driven into computers trying to make sense out
of ramjet engine controls and who left the aircraft industry because the
task was nigh impossible.

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