"peter"  wrote:   
      
   >In looking at a ramjet/scramjet diagram, it seems that the burnt gas would   
   >want to go in both direction: towards both the inlet and the outlet. Since   
   >there is no valve to prevent a back flow, why wouldn't this push the air out   
   >of the inlet and stall the engine?   
      
   I don't think _any_ of you guys get it.  These are all plausible-sounding   
   excuses that don't really explain anything.   
      
   You have a presurized chamber.  Normally gas in a pressurized chamber is   
   equal in all directions, regardless of flow. If the inlet and exhaust ports   
   were the same size, total inlet and exhaust pressure would be equal, which   
   would seem to imply zero net thrust.   
      
   First point: so far as I understand, the exhaust port is a lot larger than   
   the inlet port, so net thrust is forward.   
      
   Second point: forward motion and duct design cause inlet pressure to be   
   greater than chamber pressure, so inlet air does not get blown back out the   
   front.   
      
   Third point: in hypersonic combusion, air flow is a matter of inertia, not   
   pressure.  The air flows too fast for pressure to propagate.   
      
   These are all conjecture.  I have no expertise in this field other than   
   having sketched a idea for a nuclear-powered ramjet engine in grade school.   
   Please explain where I'm wrong.   
      
   /kenw   
   Ken Wallewein   
   K&M Systems Integration   
   Phone (403)274-7848   
   Fax   (403)275-4535   
   kenw@kmsi.net   
   www.kmsi.net   
      
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