# Batch 2020-batch-01 #

8 grains of 75mm KNSB, intended to be a reload for my long purple case.
with Loki-style #58 nozzle.  Grain length 5.125" with 0.125" spacing per 
grain planned using o-rings.  Delrin coring rods of 0.75" diameter since 
that's what I have bases and caps for, then bored out to 0.875" final ID 
before assembly.

Kuker's Motorsim says this should be a 43% M-2690 with a slightly progressive
burn about 2.5 seconds long, using 5355g of propellant or 73% volume loading,
and a max pressure of 825 psi.

Since this is too much propellant to handle in one batch, we'll plan to use
two 2700g batches, the formula for each of which is:

* 65% KNO3, 1755g
* 35% Sorbitol, 945g
* 1% red iron oxide, 27g, added after melt
* 41 drops Polystep-B1, added before pour using eye dropper

This formula is completely fluid with 225F indicated on the Presto Multicooker,
but viscosity is noticeabley lower making for easier pouring at 250-275F.

These grains were cast on 2020.08.31.

## Results ##

The 5.125" grains were poured to a 119mm fill line, and then an 0.75" Delrin
coring rod was twisted down into the goo puncturing foil over the coring rod
hole at the grain base.  About 18 hours later, the grains were "topped off" 
and smoothed level to compensate for shrinkage.  The coring rods were pulled 
about 48 hours after casting, and each grain was observed to have some bubbling 
around the base of the coring rod, presumed to be due to air below the foil on 
the casting base pushing up as the rod went down.  We should arrange for 
explicit venting of that in the future.  The top faces of the grains were knife
scraped smooth, the cores were bored out to 0.875", and the bottom of each grain 
was chamfered around the core to eliminate the bubbly bits.  Thus, the grain 
masses were highly likely to be less than anticipated.

* Grain 1, 630g gross, 16.21g casting tube, 613.79g net
* Grain 2, 634g gross, 16.20g casting tube, 617.80g net
* Grain 3, 640g gross, 16.14g casting tube, 623.86g net
* Grain 4, 632g gross, 16.17g casting tube, 615.83g net
* Grain 5, 626g gross, 16.34g casting tube, 609.66g net
* Grain 6, 628g gross, 16.11g casting tube, 611.89g net
* Grain 7, 628g gross, 16.17g casting tube, 611.83g net
* Grain 8, 636g gross, 16.28g casting tube, 619.72g net

Average casting tube weight 16.2g.  Measured total propellant mass of 4924g, 
or about 616g per grain, which is 92% of what Kuker's simulator projected.

Borrowed Terry's Loke #58 nozzle, which is a few thousandths over-sized.

The as-built motor is projected to be a 30% M-2300 or so.

Flight attempted at Airfest 2020 on Monday morning, CATO just off the rail.