# Re: The actual running Archie paper...

```--Original Message-- From: James R. Cunningham : Monday, May 10, 1999 02:16
AM

>
>
>John V Jackson wrote:
>
>> Rockets push against their propellant which is initially travelling at
their
>> speed.  Jets push against the air which is travelling backwards relative
to
>> them.  In order to gain some forward impulse a jet has to push the air
>> backwards in an absolute sense; a rocket can enjoy a forward impulse even
>> though the exhaust gases might theoretically be moving in the same
direction
>> as the vehicle.
>
>John, no offense - but this isn't how rockets and jets work.  Both work by
>ejecting a mass rearward at a significant velocity.  Neither push against
>anything behind them, or against their own propellant, and in fact both
will
>work more effectively if they are exhausting into a vacuum.  I designed and
used
>a jet thrust exhaust augmentation system for a prop driven plane we flew in
the
>Denver-Oshkosh cross-country air race two years ago, and could send you
some of
>the math if you wish.  And also some references by others in regard to the
same
>subject, and pointing out the same fallacy, which is quite commonly made.
>
>But we are drifting away from dinosaurs, so probably should continue this
>off-list.
>Jim
>

I do take offence Jim, because actually it IS how they work, since to eject
mass rearwards is the same thing as to push it.  I suppose you'd also insist
that propeller driven planes don't push against anything either.  How about
bikes?  "No" you'd say "They don't push, they exert a force on the ground."
If you can't see that "push" is shorthand for "to exert a force" then you
shouldn't contribute to this kind of list, you should restrict yourself to
formal publications.

You are desperate to project onto me the error that in order for a boat to
obtain thrust by squirting water out of the back of it, the stream of water
has to hit something.  You then try to justify this by giving us details of
some air race you've taken part in.  It would have been better if you had
just taken the trouble to read what I said carefully in the first place.  I
won't continue discussions with you on this or any subject on or off list in
future as it has been clear to me for some time that your interests lie
in being a patronising show-off, and pretending to be a disinterested
authority
while supporting a particular side.

JJ

```