PVC Motor Tests, Titanium Rcandy
 
Discovered a way to make a simple molding jig.  A hole saw makes just the right cut to seat a short section of 1 inch OD aluminum tubing.  It also produces a nicely-centered hole in the middle.

After literally months of deep thought, it finally occurred to me how to get a reduced peg on one end of the coring dowel that is perfectly centered.  Use the table saw!  I lower the blade until it is just barely over the saw table, and roll the dowel over it until it is cut down just that amount. 

It took several tries, but doweling is cheap.  Once I got the saw set up just right, I made several. 

The brown flap is typing paper covered with plastic mailing tape.  It is rolled up and inserted in the molding tube to keep the propellant from sticking.  It emerges with the grain and serves as an airtight wrapper, at least for the outer surface.
Here is a bare grain of plain rcandy made in this mold.  It is ready for an inhibitor to be added, or else fired like it is.
Notice in the top picture there is a silvery thing lying to the right of the mold.  That is a grain that has been molded, cooled, unwrapped, and covered with 3 layers of aluminum foil duct tape. 

The tape is cut about 3 inches too long, so that it can be pinched shut to seal the grain.  I believe this will make a pretty good package for storage of these hygroscopic grains

Before loading, the ends are cut off to expose the propellant inner surface and ends.

Now my imagination takes a leap, and envisions having several grains sealed in such a wrap, loading them in unison into a casing, and storing indefinately.  Then at firing time, one pokes a sharp thing through the nozzle to make a hole in the wrapper, inserts an ignitor, and all is ready to go.  Right?  Poor-man's Cesaroni load.  "Povera-38?"
Here is another grain made in the mold with the aluminum-foil duct tape inhibitor added.  
This technique is way too easy.  There must be something wrong with it.
This grain will go in a  1 inch ID PVC casing.  The end-cap has been drilled with a 9/16ths inch wood bit, and a 5-minute nozzle formed.  This is done by packing Bentonite clay into that end, drilling a nozzle throat with a 23/64ths inch bit (.281) and flaring the exit with a sharp pair of scissors.
The Japanese magnoila is in bloom.  Isn't it lovely?
Here is Motor #1 on the test stand, 2/29/04A
Specs are: 
Grain:  Rcandy with 8% Ti and 1% Fe2O3
Grain type:  Inhibited, al foil tape
Length: 
Test 1, 2-29-04A  Click Here for a video of this test (1 meg, 4 seconds)

Test 2, 2-29-04B - Virtually identical to A except no Fe2O3 in the propellant.
Click Here for a video of this test (1.3 meg, 5 seconds)

Both motors burned well, despite low Kn ratios.  I wonder if the Ti helps out here?

I havent' yet analyzed the test stand date, but at a glance thrust seems to average 10 to 12 lbs for 0.8 second or so, roughly 40 N-seconds which is in the ballpark of expectations for this propellant.
3/1/04A
Happy March to you!  Today's treat is a double.  Two of the 2.5 inch grains in a single casing, same nozzle throat diameter.  This will be a much more vigorous motor than yesterday's tests.
The grains are made from odds and ends of propellant.  Both contain a little zinc and a bit of Ti.  The one on the left also contains 1% Fe2O3.  It is placed at the head-end of the motor to ensure ignition. 

Not very scientific, just do it and see what happens.  I indulge myslef a few of these now and then, and sometimes learn some unexpected things.  Like what  they say about Education:  It's what you got instead of what you wanted.
Test 3, 3-1-04A.  Click Here for a video of this burn.  (1.3 megs, 5 seconds)

Good burn, but funny "squeak" at the end.  Nozzle eroded significantly, one inhibitor badly burned, the other completely missing!  I suspect that the squeak was the missing inhibitor being ejected from the motor. 
Here is that eroded nozzle.  It went from 0.281 inch throat diameter to 0.45 inch.  No doubt this reduced the Kn ratio a bit.
Believe I might have found the limits of this quick-and-dirty inhibitor. 

Not to worry.  I can still apply a better inhibitor, then cover it with foil tape to seal the package.  I have a 38mm version of one of these I made in November '03 which I plan to test in May '04.  By then it will have endured quite a range of atmospheric conditions, most of them humid.  I will let you know how it works!
 
 

Jimmy Yawn
jyawn@sfcc.net
www.jamesyawn.com