Ken,I don't think it was an igniter over-pressure. The video appeared to show
very slow ignition and pressure build-up. I don't think the motor had a nozzle
closure disc so motor failure was not due to igniter effects. Much more likely
some sort of grain failure.Barry
On Tuesday, February 21, 2023 at 08:27:12 PM EST, roxanna Mason
<rocketmaster.ken@xxxxxxxxx> wrote:
John I understand your potion perfectly as I used to build zinc/sulfur motors
and didn't even test them, "just let'er rip"! By the motor design description
It was most likely a grain failure but was it a crack or did the ignitor cause
the over press or.....?
That happened to a GALCIT motor which had dozens of successful flights but when
the ignitor design was changed it destroyed the 5" HiVar case made of 4130 high
carbon steel. Took out the launcher too.I hope you find the problem and achieve
your dream.
Ken
On Tue, Feb 21, 2023 at 11:30 AM John DeMar <jsdemar@xxxxxxxxx> wrote:
Ken, The one thing it may tell us with some certainty is that the cause
wasn't the hardware. Even with an aluminum case, it should have held 1500 psi.
But, it would be helpful to see the retaining ring, to see if it's intact or
sheared or rolled.
Regarding the instrumentation, burn time plus success is good enough for the
relatively low cost of this motor. The loss of any sensors and related
equipment could exceed the investment in the test article.
-John DeMar
Las Cruces, NM
https://www.linkedin.com/in/jsdemar/
On Tue, Feb 21, 2023 at 12:02 PM roxanna Mason <rocketmaster.ken@xxxxxxxxx>
wrote:
Other than the test video, without any instrumentation, post test hardware
inspection (and speculation) will be all you can do to conduct your
analysis.One channel minimum of Pc, chamber pressure, trace would be helpful.
Even an analog pressure gauge on video would give at least a low frequency
reading and maybe give the failure pressure...Posting some pics of the post
test hardware would give more eyes on the subject and more chances of zeroing
in on the overpressure mechanism.
Ken.
On Tue, Feb 21, 2023 at 8:25 AM John DeMar <jsdemar@xxxxxxxxx> wrote:
Rick, From those specs on the case and screws, I get about 2800 PSI to shear
the screws (derate grade 8 tensile strength by 50%). Assuming 1/4" wall
standard-grade oil pipeline steel, the case should have deformed the holes at
2000 PSI and sheared at 2400 PSI. High grade pipeline steel would shear at 3000
PSI. I didn't derate for temperature based on the short time to heat soak.
So, plenty of margin on the hardware for a normal operating pressure in the
1000 to 1500 PSI range.
-John DeMar Las Cruces, NM https://www.linkedin.com/in/jsdemar/
On Mon, Feb 20, 2023 at 7:18 PM Rick Maschek <dmarc-noreply@xxxxxxxxxxxxx>
wrote:
The case was approximately 12 inch by 9 feet long, quarter inch wall oil
pipeline steel pipe.24 grade 8 half inch bolts in two rows holding the quarter
inch wall steel retaining ring.The forward bulkhead was a steel plate welded in
the motor case.5 grains of KNSB propellant 20 inch long with the cores varying
from 2.5 inches at the bulkhead to 4 inches at the nozzle We used aluminum
motor cases as our mandrels covered in silicon sheet and greased for
release.The nozzle grain weighed in at 124 pounds with the others slightly
heavier because of smaller cores. The nozzle had a 94% ideal density, normal
density for me is 96-98%
I was up all night Thursday and much of Friday night helping student teams so I
left soon after our 12 inch test.Not sure what caused the anomaly, lots of
speculation and guessing. I'm still investigating the cause.We had two previous
successful 12 inch KNSB sugar tests, one with 2 grains and one with 3 grains.
This test had five grains and was designed to be progressive to test our three
piece safety nozzle.Design pressure at start up was higher than the two
previous 12 inch tests.
Flew a 4 inch KNSB motor just a couple hours before the 12" test UCLA Rocket
Project Avionics & Recovery test
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UCLA Rocket Project Avionics & Recovery test
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https://www.youtube.com/watch?v=jWspWbTCXbM
Rick