Some observations on sounding rockets | Project planning and misc | Forum

I've spent some time lately reading up on as many sounding rockets (and in particular ones designed by university teams) as I can to get a better feel for the norms in the field (in particular looking at L:D ratios) and have made a few observations that I think are relevant to OHKLA as we move forward:

• So far I have not seen any rockets in which the outer surfaces of the combustion chamber or oxidiser tank become part of the rocket's wetted area during flight, like the current OHKLA concept diagrams call for.  Everybody is placing their tanks and chambers inside aerostructures.  We should strongly consider this.
• Almost everybody seems to have some kind of thin layer of thermal insulation between the outer surface of their fuel grain and the inner surface of their combustion chamber, which we have never discussed.  Paper phenolic seems a common choice of material for this.  However, most chambers are made of aluminium (lower melting point than steel), so if we go with steel this may not be necessary.  Also, most fuel grains are HTPB which may conduct heat better than PE, which would also reduce the need for this.  We should at least be aware of the possible need for this.
• Almost everyone seems to use the same arrangement of the parachute system, which looks like this:

  [NOZZLE = COMBUSTION CHAMBER = OXIDISER TANK = DROGUE CHUTE = BAY 1 = MAIN CHUTE = BAY 2 = NOSECONE >

  The avionics and payload go in either BAY 1 or BAY 2 above, it seems to vary.  I have to admit I don't fully understand how this works, but it is almost universal, so it is obviously the accepted way to go about it.  We should strongly consider this arrangement.

• Fibreglass is a fairly common material for nosecones and fins.  It has an extremely high melting point (technically it doesn't actually melt, just becomes soft) and low thermal conductivity, and is fairly low weight.  I think we should definitely consider it for at least the nose cone – fins could easily enough be made of aluminium which would probably have a better chance of enduring the shear forces.
• As an alternative to lathing up a metal nozzle like the one in our current diagrams, it seems relatively common to take a cylindrical block of graphite, lathe out the interior shape of the nozzle, and just slide the whole cylinder into an appropriate shaped open-ended tube at the end of the rocket.  Choosing between these alternatives is something that should be on the Design Task Tree.
• Spin stabilisation via canted fins seems very common.  The steady-state spin rates seem to be no greater than 6 Hz.