Forgot the last question.
The only way you can really do that with any sort of confidence (talking ball
park stuff here) is to gather your measured pressure data and your propellant
mix. Enter your propellant into the PEP tool in (perhaps) GrainsCAD to gather
the expected theoretical thrust coefficient with your nozzle’s expansion ratio
and the ambient conditions of the test and the chamber pressure (from
measurements) and say a setting of 50% frozen-shifting reaction flow through
the nozzle. That will provide you with a theoretical thrust coefficient for a
particular pressure point. Do that for a range of chamber pressures experienced
with your test.
So, for each pressure data point in your acquisition, you can multiply that
chamber pressure with your nozzle throat area and the theoretical momentary
thrust coefficient to gather the thrust at that pressure interval. From that
you can multiply the mean of those thrust values with the burn time to gather
total impulse.
A bit of dicking around and ideally done on spreadsheet so you can perhaps
model those theoretical momentary thrust coefficients from a polynomial
expression or whatever suitable equation to reduce the qty of data points
required.
Troy
From: arocket-bounce@xxxxxxxxxxxxx <arocket-bounce@xxxxxxxxxxxxx> On Behalf Of
Ramizcan Umut Seckin
Sent: Thursday, February 23, 2023 3:40 AM
To: arocket@xxxxxxxxxxxxx
Subject: [AR] Re: Subject: Re: S-26.500 KNSB Sugar Shot test tomorrow
Troy,
Isn’t it easier using an Arduino laying around (also cheaper) instead of the
DataQ module?
I never tried transducers before, do you need to make a hole in the bulk head
or can it be done without (used load cells till now)?
Last question is it possible to just use a transducer in order to make a
impulse graph?
Raum
On 21 Feb 2023, at 22:47, Troy Prideaux <troy@xxxxxxxxxxxxxxxxxxxxx
<mailto:troy@xxxxxxxxxxxxxxxxxxxxx> > wrote:
John,
Seriously, you can pick up a cheap Chinese transducer up for not very much at
all these days eg:
https://www.aliexpress.com/item/4000704177712.html?spm=a2g0o.productlist.main.37.36306a5c49iiuO&algo_pvid=8e31b2f2-0268-4b88-aa52-48ab4ca50125&aem_p4p_detail=202302211321284979106786310800001783306&algo_exp_id=8e31b2f2-0268-4b88-aa52-48ab4ca50125-18&pdp_ext_f=%7B%22sku_id%22%3A%2210000006206659883%22%7D&pdp_npi=3%40dis%21AUD%2124.09%2122.89%21%21%21%21%21%40211be59e16770144882715524d06f7%2110000006206659883%21sea%21AU%21100784320&curPageLogUid=jwiSi6bY02xM&ad_pvid=202302211321284979106786310800001783306_19&ad_pvid=202302211321284979106786310800001783306_19
and a basic DataQ module for $50 which you shouldn’t lose in a mishap
https://www.dataq.com/products/di-188/
Not much investment provided you have a PC to run it with or even some flight
electronics have the capability to log additional data channels. Craig
Strudwicke’s old flight computer was one example of that. In fact, my
multimeter does data logging.
I mean, for *candy* motors, you generally don’t worry, but for something this
size – as you would know, there’s a fair bit of work in producing something on
this scale irrespective.
Troy
From: arocket-bounce@xxxxxxxxxxxxx <mailto:arocket-bounce@xxxxxxxxxxxxx>
<arocket-bounce@xxxxxxxxxxxxx <mailto:arocket-bounce@xxxxxxxxxxxxx> > On Behalf
Of John DeMar
Sent: Wednesday, February 22, 2023 6:29 AM
To: arocket@xxxxxxxxxxxxx <mailto:arocket@xxxxxxxxxxxxx>
Subject: [AR] Re: Subject: Re: S-26.500 KNSB Sugar Shot test tomorrow
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
<mailto: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
<mailto: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
<mailto: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
<https://www.youtube.com/watch?v=jWspWbTCXbM> UCLA Rocket Project Avionics &
Recovery test
<~WRD0000.jpg>
UCLA Rocket Project Avionics & Recovery test
<https://www.youtube.com/watch?v=jWspWbTCXbM>
https://www.youtube.com/watch?v=jWspWbTCXbM ;
Rick