Batch 2017-batch-03
6 grains of 29mm using erythritol, intended to be a reloads for the longest GMA 29mm snap-ring case. Grain length 41mm with 1mm spacing per grain, so we'll make the casting tubes 42mm long. Delrin coring rods of 5/16" diameter.
Formula for a batch size of 175g:
- 65% KNO3, 113.75g, taken from the big bucket
- 35% Erythritol, 61.25g
The multi-cooker was preheated to about 250F with the lid on. Temp was increased during melting to 300F indicated.
These grains were cast on 31 May 2017.
Simulation says:
| 29mm 6-grain Erythritol #14 | |||||
|---|---|---|---|---|---|
| Rating: | 43% H-162 | Max Pressure: | 5.92 MPa (859 psi) | ||
| Total Impulse: | 216 Ns | Specific Impulse: | 133 s | ||
| Max Thrust: | 206 N | Volume Loading: | 70% | ||
| Average Thrust: | 162 N | Fuel Mass: | 165 g | ||
Results
Average casting tube mass 1.13g.
Coring rods extracted easily, new hickory tube caps came off without too much effort. Slight cleanup at the top of each grain since propellant always seems to fillet around the coring rod. Grain average fill levels looks pretty good, with on the order of 1mm space at the top as expected.
- Grain 1, 26.57g gross, 25.44g net
- Grain 2, 26.63g gross, 25.50g net
- Grain 3, 26.65g gross, 25.52g net
- Grain 4, 26.01g gross, 24.88g net (visible undefill)
- Grain 5, 26.51g gross, 25.38g net
- Grain 6, 26.75g gross, 25.62g net
Total of 152.34g propellant, vs 159g simulated.
Note that after casting grains and cutting a liner to 10.0", I realized I'd mis-measured the case, and we actually had 10.4" of liner/propellant length to play with! Fix this for the next time we make grains... For now, we'll fly these grains in a correct length liner and live with the fact that we could have put another 0.4" of propellant in the case! That'd be another 13 Ns according to the simulator...
With a 10.40" liner, 14/64" nozzle throat, buna-n o-rings, simulation says this reload will be a 37% H-155, 208 Ns, with about a 1.2 sec burn.