Re: [NTLK] newtontalk Digest V2 #467

From: Steve Hix (
Date: Tue Jun 25 2002 - 22:00:32 EDT

On Tuesday, June 25, 2002, at 06:32 , wrote:

> Date: Mon, 24 Jun 2002 09:48:52 -0400
> Subject: Re: [NTLK] up in the sky
> From: "Eric L. Strobel" <>
> on 6/23/02 6:15 PM, Karel Jansens at wrote:
>> Um, IANAE but... I don't think the SR-71's jets ever operate as
>> ramjets.

Not as pure ramjets, no, but most of the thrust and mass flow at cruise
never goes through the turbines.

>> The huge cones (which are adjustable) serve to keep the air intake
>> speed
>> below mach 1. It is true that the compressors don't do much
>> compressiong
>> anymore at cruise speed, but they keep churning...
> Yes and no... As Mark Bock pointed out, at operating speed a
> substantial
> amount of the compression is coming from the ram pressure of the air.
> Depending on the speed, one might term it a ram-assisted turbojet or a
> turbo-assisted ramjet. But I don't recall anyone ever terming it as
> simply
> a ramjet.
>> Technically I'd say the V1's engine is a ramjet because it gets all its
>> compression from the air itself but, because it operates at low speed
>> (way
>> below mach 1), it needed mechanical aids to achieve that compression,
>> i.c.
>> the valves in the combustion chamber.
> No, think of it more as a linear internal combustion engine.

It's called a pulse jet. It has a series of spring-loaded vanes at the
front of the
engine, open to admit air, which is mixed with fuel, and when the fuel is
ignited, the pressure rise inside the engine forces the vanes shut,
leaving no
way out but the exhaust end.

> The distinction is that in a true ramjet, the inlet compresses and
> slows the
> incoming supersonic air flow to subsonic speeds.

That is one type of athodyd, there is also the "scramjet", in which the
gas flow
never drops below Mach 1.

> The thermal energy
> released in this process is so great that it heats the fuel-air mixture
> to
> the ignition point. In the buzz bomb-type pulse jet, as in an internal
> combustion engine, IIRC, the ignition source is separate. (That is,
> it I
> don't think it was 'dieseling'.)

No, you're right, it is ignited with a spark plug. Pilot reports (there
was a
manned test version of the V1) were that flying it was quite unpleasant.

>> Isn't a supersonic ramjet called a 'scramjet'?
> That's a ramjet where the fuel and air mix and combust while the
> incoming
> air is still moving supersonically, in sharp contrast to the ramjet
> operation (as outlined above). The reason it's taking so long to
> build a
> scramjet is that mixing and supersonic flow are damn near mutually
> exclusive.

The Russians have got a few of them to work, as has NASA (briefly).
that can survive operating conditions are the biggest problem right now.

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