John Carmack,

Have you considered the van control system used by Robert H. 
Goddard?  The advantage to his system is the vanes would be 
most of the time out of the jet, thus less erosion and less ISP hit.  
The only disadvantage is it would only work for pitch and yaw 
control, no roll.  However for a multiple engine system the vanes 
could be configured to also then control roll.

Also for anti slosh baffels have you considered using some 
telescoping tubing mounted on the end plates of the big tank and 
on the outer tube mount some rolled sheet metal with perforations 
so that the rolled parts would spring out when the assembly was 
slid into the access port?  This would allow a large area baffle to be 
installed without having to deal with the access problems of the 
wound tank.  My concern is that sloshing will couple with the flight 
control in a distructive open loop condition with a significant partial 
fuel load.

Just some thoughts.  Wish I was in the area.  I love following your 
progress.  Its so cool to see a private DC-X system comeing to life 
that has such promising low cost and have nice safety features 
such as a fairly benign propelent.

Keep on Rocketing!

 - Edward Rupp


John Carmack wrote:
> 
> >
> >     That's all very well. But I have to ask myself: Where are the 
existing
> >rockets that use jet vanes for steering? AFAIK, they all use 
engine
> >gimballing -- which suggests that vanes have some shortcoming.
> >
> >     (Yes, I know I'm in PCBH territory here. It's a region well 
known to
> >me. <g>)
> >
> >Chris
> >--
> >PCBH -- politely corrected by Henry
> >_______________________________________________
> 
> There are really only two downsides:
> 
> With hotter rocket engines, vanes have erosion problems.
> 
> You lose a couple % of your Isp due to vane drag.
> 
> The conventional space launch industry "wisdom" places an 
inordinately
> large value on Isp, at the expense of almost all other factors.
> 
> A great many missiles do still use jet vanes as a pragmatic and 
cost
> effective setup.
> 
> John Carmack
> 
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