Ben, we are using 2", 3", 3", 3.5" and 4" steps.
I have two sections of tapered aluminum street light pole that I thought would
work great for large motors but when we tried it on our 8" eight foot tall
motor, I was in hopes that once it was pulled an inch or so it would easily
slide out...nope. We found that much surface area on the long mandrel was too
great and we ended up breaking up the propellant during removal. I'm sure the
pressure generated by 7-8' of propellant on the lower part of the mandrel was
just to great to be easily removed.
I've used compression on my 4-6" grains in the past but stopped in the last
year or two but with this experience, I might rethink. One of the issues with
grains of this size is the timing and fit of the compression disk. The heat of
all this propellant keeps the top liquid for a long time (hours) and the
compression disk would have to be placed on top when the propellant was just
right...to soon and it pushes out liquid and if too 'hard' it becomes useless
for compression. Maybe I've just gotten use to heating the propellant just hot
enough to melt/pour and no hotter. This last final grain was done after the
fourth grain and I think with daylight running out the temperature was turned
up to melt faster. Hotter melt means more expansion and more contraction when
it cools. Would that be right?
I still remember our 'Double D coreless' grains. I cast them without internal
cores, two flats were made on the exterior opposite sides and the rest was
epoxied with fiberglass to inhibit. The grain burned on the outside inward. The
epoxy fiberglass seemed to work but that was on motors burning for 3-4 seconds.
I think I would like to do the epoxy and new casting tube method similar to
what David said. If it works ok, I'm almost wanting to do that with the four
other grains.
Thoughts on the epoxy? On Monday, December 19, 2022 at 01:26:57 PM PST, Rick
Maschek <rickmaschek@xxxxxxxxxxxxxx> wrote:
Thanks for the input and suggestions, all have been discussed and I've used
several in the past but on 'smaller' 4 to 6" grains.Our two piece 'safety
nozzle' is built with a 6" hole in the convergent piece. The 3.3" throat and
divergent cone slides in from the outside and is bolted on. If the pressure
gets too great it is designed to blow off well below casing burst strength,
greatly reducing the pressure out the 6" diameter 'hole' and saving the rocket
while still thrusting vertically. I've never yet tested the design but it seems
like it would/should work.
I used up my supply of sorbitol on this 635 pounds of propellant motor and was
looking to buy another 1,000 or more pounds of sorbitol...STICKER SHOCK at the
current inflated prices for the next purchase. Mike Brinker has offered some if
we need to cast a new grain. The last time we bought some, I think we bought
2,000 pounds and split it 3 ways. I found a place that's even cheaper but when
I called that price was for a 150,000 pound bulk shipping container full from
China...anyone want to go in for half?
I am inclined to coat the outside of the propellant and the inside of the new
casting tube with epoxy, and slide the new casting tube over it while insuring
enough epoxy on top to get pulled in so no space is left empty as the tube
slides down. If some of the epoxy stays on top that will be fine as we had
thought about inhibiting the top surface of the bulkhead grain to limit the
heat to the bulkhead although we expect several inches of hot liquid slag to
form on the bulkhead. We also considered and still might leave a 1/2" disk of
plywood insulator on the bulkhead. As with our previous motors, we expect
EVERYTHING flammable inside the motor to get consumed...casting tubes, O-rings,
etc. Nothing was found inside the steel case post-burn except the thick 4"
layer of slag on the bulkheads.
Eric mentioned 'flex seal' yesterday. That would be the easiest and least
expensive to do but I've never tested it in a hot environment for a 15-20
second burn.
Thoughts? On Monday, December 19, 2022 at 11:09:58 AM PST, Ben Brockert
<wikkit@xxxxxxxxx> wrote:
You mention “smallest core”: are you going for constant velocity through all
the grains, or a couple steps?
Weird to say, but congrats on not firing it. There are many projects where’d
they get go fever and say “ah well we’ll just fire it with one less grain, it
will be pretty close”.
On Sunday, December 18, 2022, Rick Maschek <dmarc-noreply@xxxxxxxxxxxxx> wrote:
Test firing was scrubbed, grain #5, the bulkhead grain with the smallest core
and the last one to be cast showed some casting tube debonding. Eric slit the
casting tube and we peeled it off. The Good news is that the entire grain
looked good, no cracks and only a couple of tiny voids (like small bubbles).
Surprisingly, considering it has the smallest core, this was the hardest
mandrel to remove with Eric having to pound on the aluminum motor tube to
remove it. The grain was very solid.
We are discussing how to repair it or if we make a new one.
On Sunday, December 18, 2022 at 10:43:55 AM PST, Daniel Kirk
<dk54321@xxxxxxxxx> wrote:
Can't wait to see the video!
On Sun, Dec 18, 2022 at 12:27 AM <dustin@xxxxxxxxxxxxxxx> wrote:
Your aren't going to static test it in that truck bed are you ?
Just kidding, I couldn't resist.
All the best,
Dustin
On 2022-12-16 09:23, Rick Maschek wrote:
Tomorrow may be the make-or-break day for Sugar Shot.
We will static test our 12" (300mm) five grain S-26,500 KNSB motor
with a total impulse of 355,000 Nsec
Finished 9' (2.7m) long motor case being transported to FAR
Rick
