Erm......may I suggest 'TINSTAAFL' (not that I'm biased in way, shape or form
).
You don't get something for nothing.
There is no such thing as a free lunch.
There is
always a cost in doing work.
Pressurising the airstream must have a cost. Screwing around with its pressure/density/temp. by playing around with the duct(s) through which it flows is going to result in an increased amount of drag.
I realise that what I've said is more of an idealogical statement than a 'proof'.
Think of it this way:
Any change to a molecule's momentum ie speed/direction/mass requires an addition of energy. The
only energy being added comes from the fuel being burnt.
This in turn is seen by a higher fuel flow for a given amount of thrust, or a lower thrust for a given amount of fuel, when compared to a situation where there is (for the sake of argument) no such thing as loss of energy due to a change in momentum.
Bit philosophical I know, but in accord with Newton et al...
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Now all I need is some smart arse relativitist or quantum theorist to come along...
[This message has been edited by Tinstaafl (edited 25 May 2001).]