Recrystallized KN/Sucrose loads for Dr. Rocket casings

The Project:  To develop a safe, reliable, and effective reload for Aerotech/Dr. Rocket motor casings using recrystallized KN/sucrose propellant.

The Process:  To carry over techniques learned largely through my PVC-motor tests, and further refined in the cast-aluminum casings tests.

Procedures for making recrystallized KN/sucrose and for making Bates and other grain formations of this propellant.  These processes are still experimental, and so further refinements will be illustrated here and there.

Motor casings and components are available from Aerotech and their distributors, and Dr. Rocket

Nozzles, O-rings, washers and other parts are available from RCS Rocket Motor Components

O-rings in quantity (and many other bits of hardware) are available from McMaster-Carr

"High Temperature Gasket Material" was purchased from a local auto-parts store



Test 1
8/31/02a  Static test in 38/240 casing
Propellant:  recrystallized KN/Sucrose, burning at 9 seconds per inch at one atmosphere
Configuration:  two "inhibited" grains, 2 inches long, 1.3 inches OD, 3/8 inch core, wt:  63 grams each.
                  one 6.5 inch long grain was molded, cored, and inhibited, then cut into desired lengths on a chop-saw
Inhibitor:  one layer heavy paper self-adhered to serve as inhibitor (wishful thinking.)
Nozzle:  phenolic nozzle, throat drilled out to 5/16 inch.
Case insulation is 12 inches of manila-folder paper, rolled up and inserted into casing prior to grains.
Aft washer original Aerotech part. Forward washer cut from automotive-type "high temperature gasket material" 1/32 inch thick
Kn ratios:  Initial: 125,  KnMax:146,  Final: 114,  Max pressure: 400psi (not really, see below)
Ignitor:  Electric bridge wire with 1/4 gram black powder in masking tape
Setup:  Mounted on see-saw test stand for added drama and maybe information.  Motor is wrapped in heavy paper to get an estimate of its temperature after the burn.

Click here for a video of this test (716k, 4 seconds of video)


 

Observations:  Strong, brief thrust.  Burn time of 0.52 seconds is much shorter than anticipated.  Post-firing examination of the contents of the casing revealed that the "inhibitor" was almost entirely burned up.  This, plus the short burn time, suggests that these grains functioned as uninhibited grains for most of their burn.  Thus it seems likely that the Kn ratios and pressures were much higher than predicted.

A large part of the inner case insulation was also consumed, but the case seems undamaged.
Paper wrapped around the outside of the casing was hot and crisp, but not discolored by heat.

Assuming the outside inhibitor failed immediately and grains burned uninhibited, the initial Kn ratio would be 338 and the maximum pressure would be in the range of 1400 psi.  Thus this inhibitor failure serves as an inadvertent test of the strength of the motor casing.  Further testing will endeavor to stay well under this pressure, partly by reverting to an inhibitor that is known to work.

Weights were placed on the see-saw at the rocket motor end until it tipped.  47 pounds were required to make it tip, thus the thrust of this motor must have exceeded that level.



Test 2
9/1/02a  Static test in 38/360 casing
Propellant:  recrystallized KN/Sucrose, burning at 13 seconds per inch at one atmosphere
Configuration:  three well-inhibited grains, 1.94 inches long, 1.2 inches OD, 3/8 inch core, average wt:  55.6 grams each.
Inhibitor:  two layers manila-folder paper glued on with five-minute epoxy
Nozzle:  same nozzle as previous test, no detectable erosion had occurred, throat still 5/16 inch.
Case insulation is 5 inch width of "high temperature gasket material" 1/32 inch thick.  This makes one full turn with some overlap
Aft washer and forward washer cut from automotive-type "high temperature gasket material" 1/32 inch thick
Kn ratios:  Initial: 169,  KnMax:189,  Final: 164,   Max pressure: 550psi
Ignitor:  Electric bridge wire with 1/4 gram black powder in masking tape
Setup:  Mounted on see-saw test stand.  Motor is wrapped in heavy paper.

Click here for a video of this test (828k, 5 seconds of video)

Observations:  Good burn, nice and steady.  Burn time of 1.041 seconds is close to expectations, indicating that the inhibitor worked.

Post-burn examination of case contents revealed that the inhibitors held up well.  They were still sturdy cylinders, not badly burned on the inner surfaces.  The gasket material seems to serve very well as case insulation, as the motor was almost cool enough to handle after the burn, and the material suffered no apparent damage.  It emerged from the motor tube easily, in one piece, and with the head-end washer intact, and could have been used again.

Note that fulcrum is repositioned toward the motor end of the see-saw.  At this point I was able to stand on it and barely lift the weight at the other end.  Thus it would have required over 167 pounds of thrust to rock the stand, and this motor obviously did not go that high.  Teresa commented that the motor would not have been enough to launch me, a statement with which I was compelled to concur.  Then I wondered why she made that suggestion, and realized that "concur" means "with the dog."  Subtle, that girl.

But note that the heavy board flexes a bit under thrust load.  This brings back an old idea, and now I have the means to implement it!

    Trash plus camera makes:
Analog Test Stand

This version is a test of concept, to get enough experience that I might be able to build a "good" version.  The angled lines represent the position of the orange pointer when weights are placed on top of the motor mount.  Apologies for the wavy last line, but note that the last line, 97 pounds, was determined by the sum weight of 3 concrete blocks, balanced with one hand on top of the motor-mount while the other hand drew the line under their teetering mass.  On the next one I will suspend a large bucket and add water for weight.

My Very First Thrust Curves


Video of 9/8/02c - 38/360 case with 3 Bates grains, slightly regressive burn (500k file)
Excel spreadsheet file analyzing this test


Video of 9/9/02a - 38/360 with a single outside-inhibited grain 5.75 inches long, progressive burn (500k file)
Excel spreadsheet file analyzing this test

29 similar tests have been performed to date.  Here are the rest them.


Jimmy Yawn
jyawn@sfcc.net
rev 11/30/02