From 2f24dee781b78df3c6a71b374c182cfa2fc2f87d Mon Sep 17 00:00:00 2001 From: Bdale Garbee Date: Sun, 28 Jun 2015 22:06:07 -0600 Subject: [PATCH] more EX work --- rockets/research/test2.mdwn | 13 ++++++- rockets/research/test3.mdwn | 65 +++++++++++++++++++++++++++++++ rockets/research/test4.mdwn | 35 +++++++++++++++++ rockets/research/test5.mdwn | 76 +++++++++++++++++++++++++++++++++++++ 4 files changed, 188 insertions(+), 1 deletion(-) create mode 100755 rockets/research/test3.mdwn create mode 100755 rockets/research/test4.mdwn create mode 100755 rockets/research/test5.mdwn diff --git a/rockets/research/test2.mdwn b/rockets/research/test2.mdwn index e14465e..1c996f8 100755 --- a/rockets/research/test2.mdwn +++ b/rockets/research/test2.mdwn @@ -1,4 +1,4 @@ -# Test 1 # +# Test 2 # Trying again using the same formula as [test 1](test1.html), but different handling logistics for pouring the grains. @@ -25,5 +25,16 @@ the last grain so not clear how well it filled. Two grains stacked on each mandrel, for 4 grains total. That left enough to form a test burn rod about 3/8" diameter and in excess of 4" long. +## Results ## + +* Grain 1, 55.42g net +* Grain 2, 54.57g net +* Grain 3, 55.90g net +* Grain 4, 56.33g net + ## Observations ## +Went much better than trying to pour one large "grain" to cut later, but we +still seemed to have lots of bubble inclusions. Either need to use more +surfactant or keep everything warmer to get better grains. Possibly pour +on a vibration table? diff --git a/rockets/research/test3.mdwn b/rockets/research/test3.mdwn new file mode 100755 index 0000000..dda3d09 --- /dev/null +++ b/rockets/research/test3.mdwn @@ -0,0 +1,65 @@ +# Test 3 # + +First attempt using Erythritol. Simulation suggested that putting 5 +long grains in a 38/720 case would yield a reasonable motor. + +Formula is a simple mix of 65% KNO3 and 35% Erythritol. Both used in +granular form directly from stock. Because Scott Fintel's site +indicated near infinite pot life in the multi-cooker, We decided to +melt enough for 8 grains, or a 520 gram batch size. + +Before starting this batch, we cut our two delrin mandrels in half to +get 4 single grain mandrels. + +[Tru-Core](http://www.rocketsaway.com/html/casting_sets.html) +casting set with four bases each set up with 0.5 inch mandrels. Four +pieces of casting tube cut to grain length of 2.250 inches. + +## Process ## + +The multi-cooker was preheated to about 250F with the lid on. Temp was +increased during melting to 300F indicated. + +We poured/scooped one grain at a time, leaving the multi-cooker heating +and putting the lid back on between grains to keep the propellant at +temperature. The propellant was really hard to pour into the 38mm grains +with mandrel already in place. Lots of drips over the side. We reduced +heat to about 225F while waiting for the first 4 grains to solidify. It +was easy to pull the coring rods after an hour or so. The caps were a +bit hard to remove. + +Given how much trouble we had pouring into grains with the mandrel already +in place, we paused to fabricate some new casting bases using the CNC +router and left-over hickory flooring material. The resulting bases are +used with aluminum foil to hold a casting tube each. The casting tubes +are marked with a fill line on the inside ahead of time, then the mandrels +are pushed into place after the propellant is poured, penetrating the foil +bottom. A cap is then placed over the mandrel and casting tube to keep the +mandrel centered. This worked a lot better! We called this test 3B. + +## Results ## + +* Test 3, Grain 1, 61.78g net +* Test 3, Grain 2, 61.54g net +* Test 3, Grain 3, 61.84g net +* Test 3, Grain 4, 61.89g net + +* Test 3B, Grain 5, 60.36g net +* Test 3B, Grain 6, 61.23g net +* Test 3B, Grain 7, 60.40g net +* Test 3B, Grain 8, 60.79g net + +## Observations ## + +The new casting bases worked very well, but we did notice a problem with +the caps. When the propellant is carefully controlled to completely fill +a grain, it touches the bottom side of the flat caps when still hot and +wet. When it cools and contracts, this leaves a thin skin above a ring +of mostly air. Cutting the "skin" off the top and scraping a bit to leave +each grain with a slightly concave top so there'd be burn space between +grains left us with remarkably consistent looking and weighing grains. In +future, we might want to either fill the casting tubes slightly less, or +perhaps switch to caps with an explicit air space above the poured +propellant in hopes that all bubbles would "surface" leaving the propellant +solid and with a bit of air gap at the top of each grain's casting tube. + diff --git a/rockets/research/test4.mdwn b/rockets/research/test4.mdwn new file mode 100755 index 0000000..24329e0 --- /dev/null +++ b/rockets/research/test4.mdwn @@ -0,0 +1,35 @@ +# Test 3 # + +More KNER grains. Since we had 8 plausible grains from test 3 and +want to burn 5 at a time, we decided to cast another 4 so we'd have +enough for two motors plus a couple single-grain open air burn tests. + +Formula is a simple mix of 65% KNO3 and 35% Erythritol. Both used in +granular form directly from stock. A 275 gram batch for 4 2.25" +38mm grains. + +Used our new casting bases, now with the mandrel holes drilled all the +way through. + +## Process ## + +Same as Test 3B. + +## Results ## + +* Test 4, Grain 1, 61.50g net +* Test 4, Grain 2, 62.38g net +* Test 4, Grain 3, 60.18g net +* Test 4, Grain 4, excessive visible inclusions, set aside + +## Observations ## + +Not surprisingly, results were essentially identical to test 3B. + +Seems pretty clear that the post-casting process of having to cut off +the "skin" at the top of the grain and impart a concave shape is +losing .. means we'll never get uniform grain masses. REally need +to figure out how to do this better. + +The last grain was "poured" by spooning in material that seemed +to be clumping a bit, and we probably didn't tap it down enough. diff --git a/rockets/research/test5.mdwn b/rockets/research/test5.mdwn new file mode 100755 index 0000000..ca27d89 --- /dev/null +++ b/rockets/research/test5.mdwn @@ -0,0 +1,76 @@ +# Test 5 # + +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 + +* 65% KNO3 +* 35% Sorbitol +* 1% red iron oxide +* 3 drops Polystep-B1 + +## Process ## + +The multi-cooker was preheated to about 250F with the lid on. Temp was +increased during melting to 275F indicated. + +Individual casting tubes with fill marks, coring rod inserted after pour, +cap installed and grain tapped down. + +## Results ## + +* Grain 1, 51.56g net +* Grain 2, 52.80g net +* Grain 3, 52.30g net +* Grain 4, 51.23g net + +## Observations ## + +Pour went really smoothly. 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. + +## Flight Test ## + +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. + +The original simulator data: +
+Propellant             : propellants/knsb.xml
+Nozzle diameter        : 0.739 cm (0.291") (19/64")
+Number of grains       : 4
+L/D ratio              : 5.550
+Port-to-throat ratio   : 2.952
+Mass Flux              : 1.374 lbs/inch^2
+Mach number            : 0.697
+Propellant length      : 18.440 cm (7.260")
+Web Thickness (max)    : 1.026 cm (0.404")
+Burn rate              : 0.773 cm/s (0.304"/s) (a=7.852mm/s; n=-0.013)
+
+Total propellant weight: 216.00 g (7.619 oz/0.476 lbs)
+Average grain weight   : 54.00 g (1.905 oz)
+Theoretical density    : 1.841 g/cm3 (0.067 lb/in3)
+Actual density         : 1.582 g/cm3 (0.057 lb/in3)
+Density ratio          : 85.953%
+Specific impulse (Isp) : 106.342 s (estimated)
+Initial Thrust         : 169.37 N (38.08 lbs)
+Peak Thrust            : 182.21 N (40.96 lbs) at 34.00% (0.45 s)
+
+Kn Ini : 309.48 (488.04 psi)
+Kn Max : 330.39 (520.59 psi)
+Kn Fin : 248.87 (393.56 psi)
+Kn Avg : 309.70 (488.40 psi)
+
+Total Impulse  : 225.104 Ns (40.69% H)
+Burn Duration  : 1.328 s
+Average Thrust : 169.555 N
+
+Motor          : H170
+
-- 2.30.2