From: zenadsl6186@zen.co.uk   
      
   bob wrote:   
      
   > zoltan wrote:   
   >> I have an experimental air breathing engine that generates about 1 MW   
   >> of power in terms of   
   >> the heat output of the propane burnt. This engine has a 7 inch nozzle   
   >> and an Isp of 4000.   
   >   
   > Jet engines are not rated in ISP, but fuel consumed per hour per unit   
   > thrust.  They need air.   
      
   Isp is the same quantity as specific consumption, but inverted, except that   
   it's usually measured in seconds rather than 1/hours.   
      
   Eg one pound of fuel per pound of thrust per hour is the same as an Isp of   
   one hour or 3600 seconds.   
      
   And 4,000 s Isp is 0.9 pound of fuel per pound of thrust per hour specific   
   consumption.   
      
   The presence of air doesn't affect that (although it's absence might  :)   
      
      
   (I have no use for slugs or poundals)   
      
   --   
   Peter Fairbrother   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)