Date: 3 Aug 92 19:49:04 GMT
From: shafer@rigel.dfrf.nasa.gov (Mary Shafer)
Subject: Re: Ram jet engine in Commmercial aircraft like Boeing..

I think that you may be referring to the RAT or Ram Air Turbine.
Perhaps you've misremembered?

This is just a little turbine that folds out of the side of the plane
(more usually fighters than transports) and uses the ram air to spin
the turbine and generate enough power to keep the plane flying.  In
the F-8, for example, the RAT would keep your hydraulics going, as
well as the more important avionics.

It's not a ram-jet engine and 747s don't have it anyway.  They (747s
and all other transports that I know of) have APUs (Auxiliary Power
Units) to do the same thing.  The APU just burns Jet-A to make
electricity and power the hydraulics.

The F-16 (and the X-29 and X-31) has an EPU (Emergency Power Unit)
which burns hydrazine to make the power.  The EPU doesn't last
very long; it's just designed to get you to a good place in the
ejection envelope.