From: earlcp@idirect.com   
      
   "Charles"  :   
      
   > Earl Colby Pottinger wrote:   
   > >   
   > > I don't know myself, but I know years ago when I thought of looking at   
   > them   
   > > that the articles I read on rockets all said nozzleless design took a big   
   > hit   
   > > in the ISP.  I even thought of it again about two years ago and again   
   > dropped   
   > > the idea thinking the loss in ISP was going to be too great.   
   > >   
   > The 20% or so higher pressure at the injector end is because the   
   > combustion is not going at constant pressure as it would if there is   
   > plenty of room in a usual chamber.  The gases have to accelerate as the   
   > combustion happens.   
   >   
   > The throat is at the point where the specific volume of the gas is at   
   > its highest--where combustion is complete.  The velocity is mach 1 from   
   > then on to the actual exit, and the divergent part of the nozzle will   
   > work the same as one in a usual engine.   
   >   
   > The 1.5% or so Isp loss is that from the effective chamber pressure   
   > being 17% or so lower than it would be with a usual chamber shape.   
   >   
   > This difference is so small that some are led to trying 1:1 area ratio   
   > engines, but there may be a heat transfer problem because a larger   
   > portion of the chamber wall will be like the throat with the higher   
   > heat flow.   
      
   This may be so, but the point I was making that like so many others I blindly   
   followed what the books said instead of testing the idea myself.  How many   
   other ideas with a chance of cutting costs have not been used because people   
   are blindly following the books instead of doing a few tests themselves.   
      
   The cooling problem is interesting to a H2O2 fan.  Most rocket designs in the   
   west use the fuel as the coolant because of fears of the hot oxidizer   
   reacting to the metal structure of the engine.  However, in most combinations   
   there is a lot more oxidizer flowing than fuel.  The extra heat flux may not   
   be a problem if you are using the larger oxidizer flow to cool the walls.   
      
               Earl Colby Pottinger   
      
      
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