Trying again using KNSO with our new casting bases. We also have a real
eye-dropper now for measuring the surfactant. 4 38mm grains of
-1.875" length, using formula of
+1.875" length, 250 gram batch using formula of
-* 65% KNO3
-* 35% Sorbitol
-* 1% red iron oxide
-* 3 drops Polystep-B1
+* 65% KNO3, 162.5g
+* 35% Sorbitol, 87.5g
+* 1% red iron oxide, 2.5g, added after melt
+* 3 drops Polystep-B1, added before pour
## Process ##
These four grains were assembled in an AT 38/480 case with a random AT
delay grain from the pile of left-overs, and flown in Robert's Madcow
-Little John at Tripoli Colorado Spring Fling 2015. We used a Slim Gem
-igniter from Quickburst. Great flight! The motor seemed to come up to
-pressure quickly, and burned brilliantly.
+Little John at Tripoli Colorado Spring Fling 2015. We used a
+[Slim Gem](http://www.quickburst.net/slim_gem_igniter.htm)
+igniter from [Quickburst](http://www.quickburst.net/). Great
+flight! The motor seemed to come up to pressure quickly, and burned
+brilliantly.
+
+The airframe weighed 1200 grams ready to launch, and 982 grams post-flight,
+of which 1g or so was BP in the ejection charge, and a few grams were in
+the Aerotech delay grain.
+
+Post-flight measurement of the phenolic nozzle showed approximately an
+0.330" throat, which clearly indicates some erosion from the 0.291" starting
+point.
## Observations ##
-Pour went really smoothly. One grain looked "perfect" with the propellant
+Pour went really smoothly. Easier than previous batches, perhaps due to
+a bit more surfactant, perhaps just getting better, perhaps due to putting
+the mandrels in post-pour. One grain looked "perfect" with the propellant
settled evenly and a couple mm of open gap at the top of the casting
tube. We think this one may have been slightly under-filled compared to
the others, all of which had some evidence of propellant sticking to the
cap and leaving an uneven top surface. This resulted in some quick trim
work with a knife, ergo final grain masses not matching all that well.
+We were totally stoked that the burn time matched simulation (once we factor
+in a tenth of a second or two before the motor came up to pressure!). We
+were also pleased that the max pressure was "right on time" at about 0.4
+seconds after coming up to pressure. The regressive curve seems a bit
+exagerated in the flight accel data, which seems completely explainable by
+the nozzle throat erosion causing pressure to faill during that period.
+
+The airframe saw an average of 12 G acceleration on the way to Mach 0.6 and
+2838 feet above the laucnh site which is at 8800 feet MSL. Perfect
+recovery! Pretty cool for our first real flight test!
projects / web / gag.com / blobdiff