KNSB M for Airfest - CATO

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+# 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.