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From: megazone@wpi.WPI.EDU (MEGAZONE 23)
Newsgroups: sci.military
Subject: Re: Scramjets
Message-ID: <1990Dec5.031653.7476@cbnews.att.com>
Date: 5 Dec 90 03:16:53 GMT
References: <1990Nov27.045102.3975@cbnews.att.com> <1990Dec3.050627.2654@cbnews.att.com> <1990Dec4.003144.11017@cbnews.att.com>
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From: megazone@wpi.WPI.EDU (MEGAZONE 23)

In article <1990Dec4.003144.11017@cbnews.att.com> elec140@csc.canterbury.ac.nz writes:
>If this is true, then where is the distinction between a ramjet and a scramjet?
>Is it to do with an external combustion chamber, or is this only one
>implementation of a scramjet?

A ramjet, like a turbojet and all derivatives, slows the airflow to subsonic
speeds prior to entering the combustion chamber(s). This allows the burning
of less volitile fuels such as kerosene and also lowers temperature and
pressure stresses on the engine. A scramjet is a Supersonic Combustion RAMJET.
The combustion takes place in a supersonic airflow, requiring fuels like
liquid hydrogen or liquid methane. However the scramjet allows for much
higher aircraft speeds, there is a practical limit to how much you can slow
the airflow for a ramjet. I believe it is in the Mach 6-7 range, any figures?
Theoretically the scramjet should be able to push an aircraft up to Mach 25,
but in practice this is a very difficult goal. A scramjet must also be 
designed as an integral part of the airframe, you can't just tack them on
pylons or stick them on the fuselage like a turbojet or a ramjet. (There
are some resrictions for ramjets too, but not nearly as strict.) The MAJOR
difference between a scramjet and all other 'jet' engines is the supersonic
combustion. Scramjets have yet to fly, officially, the first aircraft to be
so equipped will be the X-30 National Aerospace Plane. Of course you may
believe in the Aurora. :-)

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