Test 11

Our first attempt at making 54mm grains with sorbitol. Grain length 3.25", core diameter 0.5" (only mandrels on hand). Casting tubes from ARR, machined a new set of hardwood casting stands on our CNC router, drilled PVC pipe caps for upper mandrel centering.

The formula used is the same we've been using with sorbitol, but in an 875g batch this time:

  • 65% KNO3, 568.75g, taken from the big bucket this time
  • 35% Sorbitol, 306.25g
  • 1% red iron oxide, 8.75g, added after melt
  • 10 drops Polystep-B1, added before pour using eye dropper

Robert noted that tamping down the material in the grains required a tweak to his process for 38mm, since the larger casting tubes and greater propellant mass meant having to hold everything together more solidly. We also noted that there was some variation (a mm or so?) in my casting tube lengths, so getting them uniformly filled was a bit fiddly. Our calculations led us to use a fill line 76.118mm from the bottom or 6.431mm from the top of the casting tubes. On a couple of the shortest-cut casting tubes, this led to a small amount of propellant contacting the inside of the pipe cap. Try harder to cut precisely next time!

These grains were cast on 1 September 2015.

Results

Dropped one grain at home, big chunk missing and maybe cracks. Decided not to use it. That left us with three "good" grains.

The case, nozzle, and closure combination used left me cutting the liner to 10.250 inches, while Loki specifies 10.375 for their 3-grain case. The total available propellant length was 9.459", so I had to trim the three grains slightly to fit. The gross masses below were post-trim. Calculating net masses will require approximation based on the overall casting tube length that remained.

  • Grain 1, ?g net
  • Grain 2, 204.0g gross, ?g net
  • Grain 3, 199.3g gross, ?g net
  • Grain 4, 198.6g gross, ?g net

10.250" liner, 8.3mm nozzle throat, buna-n o-rings.

calculated as a 39% J-477, 843 Ns, ~1.5 sec burn

Observations

1250g pre-launch motor mass, 664g post-flight motor mass.

4830g pre-launch airframe mass.