tip laminations got hot enough for the epoxy to soften allowing the carbon
fiber to be ripped off... West System is and will continue to be my go-to
epoxy for normal airframe builds, and worked great on a previous project
-that got to Mach 2.21... but with a glass transition temperature of 129-242 F,
+that got to Mach 2.21... but with a glass transition temperature of 129-142 F,
it's just not up to the challenge of staying together above Mach 3!
So, for this build, the plan was to use the same design and build techniques,
-but switch to one of the Cotronics high-temperature epoxies. Because high
+but switch to one of the [Cotronics](http://cotronics.com) high-temperature
+epoxies. Because high
temperature epoxy is seen as expensive, others have talked about using lesser
epoxy for the bulk of the fin build-up laminations and then just using
Cotronics as a top coat, or the thicker version to build up leading
## Design Details
-This is basically a "2 fins and a nose cone" design, using a single 5 foot
-length of filament would fiberglass airframe, a filament would nose cone
-with aluminum tip, and plywood fins covered with tip to tip carbon fiber.
+This is basically a "3 fins and a nose cone" design, using a single 5 foot
+length of filament wound fiberglass airframe, a filament wound nose cone
+with aluminum tip, and plywood fin cores covered with tip to tip carbon fiber.
Due to the CTI M2245 reload that was used for the first attempt not being
available for a while, the M3464 Loki Blue from Scott Kormeier at
-[Loki Research](http://lokiresearch.com) was chosen to power this attempt.
+[Loki Research](http://lokiresearch.com) was chosen to power this
+attempt.
The fins were made using high quality 1/8" Baltic birch plywood cores glued
into slots milled in the airframe tube, then 3 layers of 5.8 oz 2x2 twill
## Result and Lessons Learned
+The airframe flew on 8 July 2017 in Argonia, Kansas, at a Fun Fly hosted by
+the Kloudbusters at their rocket pasture. Everything performed perfectly
+until apogee. The maximum velocity was 1047 m/s, or right at Mach 3.1, on the
+way to an apogee of 32,635 feet above ground.
+
+Unfortunately, while telemetry shows the electronics correctly fired the
+apogee ejection charge, clearly the nose cone did not successfully
+separate. The resulting ballistic return impacted about 1.1 miles down range
+to the south-south-west.
+
+With the final telemetry frame received from about 200m altitude on the way
+down, we know impact was at about 2/3 Mach. Not surprisingly, then, what
+we found in the middle of the wheat stubble was a 3" diameter hole with 3
+slots radiating outward, and quite a bit of visible purple paint on the sides
+of the hole. Probing with a shovel handle, we learned the aft end of the
+airframe was on the order of 18 inches below ground level, and the aft end
+of the motor nozzle was at least 4 feet down! Curious to know the fate of
+the fin can that was the focus of this project, we took turns shoveling until
+the fin can was sufficiently exposed to reveal two perfectly intact fins and
+the third sheared off by impact with a fist-sized rock several inches below
+ground level. Given the heat, and lacking either a backhoe or an army with
+shovels, after taking a bunch of photos and logging GPS coordinates, the
+decision was made to abandon recovery and just fill in the hole.
+
+So, two big lessons learned.
+
+ Yes, Bdale can build a fin can that can survive Mach 3!
+
+ Getting so focused on one part of the project that you forget things
+ you know you should do elsewhere to ensure success leads to loss...
+
+What I mean by the second is that while this is the first time I've personally
+put an airframe above 30,000 feet... I've hung around other people who do it
+successfully, and I've listened to details of what they did. In hindsight, I
+"coulda, shoulda, woulda" put more attention on the apogee ejection
+event. More black powder in the charge. More confinement to allow more of
+the powder to burn before being dispersed in the lower-pressure environment
+at altitude. Using one of the spare TeleMega channels to fire an up-sized
+backup charge. Flying a TeleMetrum for full ejection event redundancy instead
+of just a TeleGPS for redundant tracking. But I didn't do any of those things,
+and lost the airframe and everything in it as a result. Yep, lesson learned!
+
--- /dev/null
+# Batch 2017-batch-06 #
+
+8 grains of 54mm using sorbitol, intended to be 2 reloads for the longest
+54mm snap-ring case currently in our possession, and/or some mix of lesser
+loads. Grain length 76mm with 2mm spacing per grain, so we'll make the
+casting tubes 78mm long. Delrin coring rods of 0.5" diameter.
+
+Formula for a batch size of 1750g:
+
+* 65% KNO3, 1137.5g
+* 35% Sorbitol, 612.5g
+* 1% red iron oxide, 17.5g, added after melt
+* 25 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 28 September 2017.
+
+## Results ##
+
+Average casting tube weight 5.90g.
+
+* Grain 1, 188g gross, ?g net
+* Grain 2, 182g gross, ?g net
+* Grain 3, 188g gross, ?g net
+* Grain 4, 184g gross, ?g net
+
+* Grain 5, 178g gross, ?g net
+* Grain 6, 190g gross, ?g net
+* Grain 7, 182g gross, ?g net
+* Grain 8, 186g gross, ?g net
+
+With a 13.250" liner, 8.9mm nozzle throat, buna-n o-rings, simulation says
+this makes a 39% J-597, 1050 Ns, with about a 1.5 sec burn
+
--- /dev/null
+# Batch 2017-batch-07 #
+
+5 grains of 75mm using sorbitol, intended to be z reloads for one of my
+resurrected CTI 5-grain cases. Grain length 120mm with 2mm spacing per
+grain, so we'll make the casting tubes 122mm long. Delrin coring rods
+of 0.75" diameter.
+
+Formula for a batch size of 3200g:
+
+* 65% KNO3, 2080g
+* 35% Sorbitol, 1120g
+* 1% red iron oxide, 32g, added after melt
+* 45 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 28 September 2017.
+
+## Results ##
+
+Average casting tube weight 16.3g.
+
+* Grain 1, 590g gross, 574g net
+* Grain 2, 594g gross, 578g net
+* Grain 3, 592g gross, 576g net
+* Grain 4, 584g gross, 568g net
+* Grain 5, 580g gross, 564g net
+
+Total propellant load 2860g.
+
+Grain 5 had an obvious "dip" in the surface, presumably where a bubble came
+up during cooling, certainly enough to account for the lower mass on that
+grain.
+
+All grains had far more "empty space" at the top than expected or desired,
+making the shrinkage while cooling very obvious. I think as the grain size
+gets larger, it might make sense to calculate fill lines based on the full
+length of the casting tube and just let the shrinkage provide the inter-grain
+spacing, rather than trying to incorporate such spacing explicitly? Just need
+to avoid filling grains so much that they "overflow" when putting in the
+coring rod. More thought needed here.
+
+Otherwise, the grains look fine, can't see any reason not to burn/fly them!
--- /dev/null
+# Batch 2017-batch-08 #
+
+24 grains of 38mm using erythritol, intended to be 6 reloads for the two
+4-grain Loki-compatible cases I machined. With only 8 casting stands and
+coring rods, these will actually be cast in 3 sets of 8, but since they cure
+quickly, there's no reason not to do it all in one melt of 1500g.
+
+Actually, we'll cast 2 sets with plain KNER, and then add 0.2% black iron
+oxide for the last set since at least one other experimenter seemed to like
+the results with that much BIO in the mix.
+
+Grains 52mm with 2mm spacing, or 54mm casting tube length, using 0.5"
+Delrin coring rods.
+
+Formula for a batch size of 1500g, with both uses in granular form from stock:
+
+* 65% KNO3, 975g
+* 35% Erythritol, 525g
+
+* 0.2% black iron oxide, 1g, added to second third
+
+* 0.4% black iron oxide, 2g, added to last third
+
+This formula seems to pour best when heated to around 300F indicated on the
+Presto Multicooker.
+
+These grains were cast on 29 September 2017.
+
+## Results ##
+
+Average casting tube weight 1.92g.
+
+* Grain 1, 54.46g gross, ?g net
+* Grain 2, 54.88g gross, ?g net
+* Grain 3, 55.28g gross, ?g net
+* Grain 4, 53.25g gross, ?g net
+* Grain 5, 53.80g gross, ?g net
+* Grain 6, 56.02g gross, ?g net
+* Grain 7, 52.54g gross, ?g net
+* Grain 8, 53.49g gross, ?g net
+
+* Grain 9, 53.47g gross, ?g net
+* Grain 10, 53.97g gross, ?g net
+* Grain 11, 54.70g gross, ?g net
+* Grain 12, 52.78g gross, ?g net
+* Grain 13, 53.20g gross, ?g net
+* Grain 14, 55.52g gross, ?g net
+* Grain 15, 53.47g gross, ?g net
+* Grain 16, 53.00g gross, ?g net
+
+* Grain 17, 51.93g gross, ?g net
+* Grain 18, 53.08g gross, ?g net
+* Grain 19, 53.35g gross, ?g net
+* Grain 20, 53.20g gross, ?g net
+* Grain 21, 55.24g gross, ?g net
+* Grain 22, 55.48g gross, ?g net
+* Grain 23, 56.38g gross, ?g net
+* Grain 24, 55.85g gross, ?g net
+
+Simulation says 4 grains of this with a #15 nozzle should be an 88% H-194
+with about a 1.4 second burn.
+
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