Re: Navy Phantom Engine Question

John Carrier wrote:


"Andy Bush" <alfakilo@xxxxxxxxxxx> wrote in message
news:Zxkog.3836$TP1.3292@xxxxxxxxxxx
It is a feature of all F-4s and is designed to control the supersonic
flow of air into the intake. The 'flat plate' (variable ramp duct) is
hinged to flex away from the fuselage as the jet moves towards supersonic
speeds. This
acts as a barrier to the incoming air and deflects the supersonic shock
wave
outside of the intake lip thereby allowing only subsonic air to enter. If
the 'splitter plate' did not do this, then the shock wave would enter the
intake throat and potentially cause engine disruptions (compressor
stalls).

That, at least, is the simplistic F-4 pilot way of explaining it!!

The more complicated Aero Engineer and Phantom driver description.

The plate separates dead fuselage air and the leading edge forms the first
of several oblique shock waves (which decelerate the air to a lower
supersonic value) As Mach climbs the back half come out to form an
additional oblique wave and also constrict the inlet to the mass flow
value
needed for the engine. Once inside the inlet the cross-section opens
slightly and a normal shock forms (supersonic to subsonic airflow). The
resultant subsonic airflow is usable by the compressor. The more oblique
shocks, the closer to 1.0 prior to the normal shock, the more efficient
the
inlet becomes. Each shock generates heat (less so across the oblique)
whose
energy the aircraft must overcome with thrust. The big heat maker, drag
producer is a normal shock that must decelerate a relatively high
supersonic flow to subsonic ... its an inverse ratio.

It can get complicated. IIRC, the F-14 NATOPS devoted about 20 pages to
inlet operation.

It shouldn't be missed that as the air slows down passing through the
shocks, the pressure goes up as well. This gets more oomph out of teh
engines.

--
Pete Stickney
Without data, all you have is an opinion
.

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