From: henry@spsystems.net   
      
   In article ,   
   Proponent  wrote:   
   >Bono's aerospike designs from the 60s feature toroidal comubstion   
   >chambers, whereas recent designs like the X-33's linear aerospike   
   >usually have several small, distinct chambers.  Why the change?  Is it   
   >just easier to manufacture distinct chambers?  Would the toroidal   
   >design tend to suffer from any nasty combustion instabilities?   
      
   The toroidal design does have "racetrack" instabilities to add to the   
   usual instability worries, and it is structurally and thermally really a   
   pain.  Chamber pressure puts the inside of the torus in compression, which   
   is much harder to deal with structurally than tension.  The fact that the   
   contraction to the throat happens in only one dimension rather than two   
   means that the throat has to be quite narrow, and the need to accurately   
   control that narrow gap aggravates the structural problems.  Finally, that   
   contraction in only one dimension means that the engine has a lot of   
   throat area (relative to chamber volume) compared to conventional designs,   
   and the throat is the area where cooling problems are really nasty.   
      
   Conventional chambers, perhaps with a circular-to-square transition in a   
   short divergent section of nozzle (after the throat), are a *whole lot*   
   easier to build and don't seem to incur a significant performance penalty.   
   Toroidal chambers are conceptually elegant but probably a bad idea.   
      
   >Speaking of the X-33, wouldn't a linear aerospike tend to be much less   
   >efficient than a cylindrical design, because the aerospike effect   
   >occurs fully only in one dimension?   
      
   In principle, they can be just as good, although there are some questions   
   about what happens at the ends.   
   --   
   "Think outside the box -- the box isn't our friend."    |   Henry Spencer   
                                   -- George Herbert       | henry@spsystems.net   
      
   --- SoupGate-Win32 v1.05   
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