Re: ERPS-list Digest, Vol 9, Issue 24

> From: [email protected]
> Subject: [ERPS] Vanes, box shealding & landing frame
>
> John Carmack,
>
> I was wandering if you folks had any concerns about the deep
> enclosure around the jet vanes?  It seems to me it may cause
> some problems with the gas dynamics for controlling the thrust
> vectoring.  It seems that as the vanes deflect a significant amount
> the gases are going to impinge on the side of the box and basically
> have the steering effects basically canceled out.  Also it would
> seem that at extreme vane deflection the back pressure behind and
> to the side of the vane and the box could be the cause of the
> stress failures of the shaft and vane that might not of other wise
> have happened in such a constricted volume.
>> ****************************************

The problem you describe has been dealt with in missles with steering vanes
contained in a shroud.  A recent AIAA article about this says the steering
loss is about 30% or so.

For John's rocket, the box-like structure surrounding the exhaust looks a
lot larger than the exhaust diameter, so that kind of steering cancellation
is less or nonexistant.  The proof is probably in that it flew...

Charles Pooley