Solid propellant test motor

The aim of this project is to design and fabricate a new revision of the DARK solid propellant test motor with the following features:

  • Easily configurable for a wide range of throat to burning area ratios.
  • Nozzles with a modular simple design.
  • Graphite throat inserts for use with high combustion temperature metal loaded propellants.

In order to reduce the amount of manual machining, the nozzles are constructed of identical stainless steel nozzle blanks. DARK test motor nozzle blanks Before final machining of the different internal nozzle geometries, graphite nozzle inserts are bonded into the stainless steel blanks with high temperature ceramic potting compound.

The final result after machining 10 nozzles with different throat areas. DARK test motor nozzles

The nozzles are all designed with an exit area ratio between 3.8 and 5.8. DARK test motor nozzles

On the first saturday of July, we went to Stold to test some new propellant compositions for the first time in the “new” solid propellant test motor. Actually the motor casing is an old design, but use the new nozzles and matching new bulkheads. Before the test, the “inside” of the nozzle bulkhead with nozzle looked like this: Test motor nozzle mounted in bulkhead

Two of the tests went like this:

Post test, the outside looked a little “smoked”: Test motor after test The small line leads to a streamer that is used to recover the nozzle and bulkhead in case of an ejected nozzle. In an “over pressure” situation, the casing is designed to fail between the external groove and the internal snap ring groove in the nozzle end. This failure mode occurs before the casing yields hoop wise, thus making it possible to reclaim the rest of the motor casing into a slightly shorter “new” casing.

The insides looked at little bit more “used”: Test motor nozzle mounted in bulkhead after test However the graphite nozzle inserts survived without any significant change in throat diameter. The soot deposits where easily cleaned of.

All in all a nice day at Stold with satisfying results for both the new test motor system and a new propellant composition with the highest aluminium loading of any succesfull DARK motor to date.