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Old 21st Apr 2013, 07:27
  #147 (permalink)  
CliveL
 
Join Date: Dec 2010
Location: Europe
Age: 83
Posts: 286
Concorde Inlet Thrust

Tomtech,

As one of the original Concorde inlet design team and as someone who has spent a fair bit of time recently trying to unpick the intricacies of the SR-71 design, I have to disagree with you gently.

The 'split' of Concorde's cruise propulsive forces generally referred to first appeared in Ken Owen's "New Shape in the Sky" many years ago. The data was given to him by members of the design team, and I think it is stretching things a bit to suggest that they 'misunderstood' jet propulsion principles.

I won't try to answer for the SR-71, but on Concorde (this is after all a Concorde thread ) the intake, engine and final nozzle all had their own attachments to the airframe so it is reasonable and possible to enumerate their relative contributions. They all produced thrust. How you divide the total up between them is a matter of book-keeping conventions and as any accountant will tell you those are convenience variables!

Specifically, the 'split' will depend on how one divides the momentum drag out between the components. I can't remember (if I ever knew) the book-keeping that went with the Ken Owen's picture, but any reasonable division results in a considerable part of the total thrust acting on the intake mounts and another sizeable chunk on the final nozzle mounting.

What I think you may be missing is that although, of course, the thrust is obtained by imparting momentum to the mass flow through the engine, and although the design objective is to make sure that the static pressure of the flow exiting the final nozzle is as near ambient static as possible, the forces which must be applied to that mass to accelerate it to its final velocity are reacted as pressures on solid surfaces on the aircraft (or engine of course). In fact all forces on the aircraft (other than gravitational) ultimately come from pressures acting on solid surfaces.

So "pressure thrust", far from being an undesirable, is in fact an essential.

I'm going to be away for a few days, but if you feel you want more detail feel free to PM me.

Last edited by CliveL; 21st Apr 2013 at 12:12.
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