Right Barry and grain failure is most likely the cause. I just thought
mentioning another failure mode affecting the grain which might widen the
suspect list.
BTW, the mode of ignitor failure in our 5" motor was the metal ignitor
housing fragmented which ripped the soft asphalt grain exposing excessive
surface area.
Which brings to mind the grain to case bond which I believe was touched on
in an earlier post. Maybe the case would act as a witness plate and show
signs of the flame front getting between the grain and case.
Ballistic forensics.
Ken
On Tue, Feb 21, 2023 at 6:09 PM Barry Jolly <1bcjolly@xxxxxxxxxxxxx> wrote:
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
<https://www.youtube.com/watch?v=jWspWbTCXbM>
UCLA Rocket Project Avionics & Recovery test
<https://www.youtube.com/watch?v=jWspWbTCXbM>
https://www.youtube.com/watch?v=jWspWbTCXbM
Rick