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  #61  
Old 06-25-2020, 10:51 PM
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5x7 5x7 is offline
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This is from NFPA 1125 but an old copy from 2007, total impulse standard deviation of 6.7 % allowed:
8.1.7 Before granting such certification, samples of a motor or reloadable motor system shall be examined as follows:
(1) Static testing, conducted at or corrected to sea level and 20°C ± 5°C (68°F ± 9°F), of a minimum of 10 samples to determine that total impulse, average thrust, and delay time comply with the following requirements:
(a) Standard deviation of the total impulse data shall be no greater than 6.7 percent of the mean measured value.
(b) No time delay shall be measured to have a variation greater than 1.5 seconds or 20 percent (whichever is greater, but not to exceed 3 seconds) from the labeled value.
(c) Average thrust shall be within 20 percent [or 1 N (0.22 lbf), whichever is greater] of the average thrust that is computed by dividing the mean total impulse measured during propellant burn time by the mean propellant burn time
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  #62  
Old 06-26-2020, 10:11 AM
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Earl Earl is offline
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Quote:
Originally Posted by 5x7
This is from NFPA 1125 but an old copy from 2007, total impulse standard deviation of 6.7 % allowed:
8.1.7 Before granting such certification, samples of a motor or reloadable motor system shall be examined as follows:
(1) Static testing, conducted at or corrected to sea level and 20°C ± 5°C (68°F ± 9°F), of a minimum of 10 samples to determine that total impulse, average thrust, and delay time comply with the following requirements:
(a) Standard deviation of the total impulse data shall be no greater than 6.7 percent of the mean measured value.
(b) No time delay shall be measured to have a variation greater than 1.5 seconds or 20 percent (whichever is greater, but not to exceed 3 seconds) from the labeled value.
(c) Average thrust shall be within 20 percent [or 1 N (0.22 lbf), whichever is greater] of the average thrust that is computed by dividing the mean total impulse measured during propellant burn time by the mean propellant burn time


Ahh. Thanks! Ok, yeah I recall having read these at some point in the past.

The allowed standard deviation is probably a bit larger than I thought, but then again I don't have any real experience at mass testing of relatively small, mass-produced rocket motors to know how difficult it is to produce a certain thrust profile over and over again within a given performance window. Like many things in life, it is probably more difficult than it first appears.

Earl
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  #63  
Old 06-26-2020, 03:25 PM
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5x7 5x7 is offline
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Quote:
Originally Posted by Earl
Ahh. Thanks! Ok, yeah I recall having read these at some point in the past.

The allowed standard deviation is probably a bit larger than I thought, but then again I don't have any real experience at mass testing of relatively small, mass-produced rocket motors to know how difficult it is to produce a certain thrust profile over and over again within a given performance window. Like many things in life, it is probably more difficult than it first appears.

Earl


Earl, it was a very interesting question, I had an inkling it was in NFPA but had no idea what it might be. The restesting is interesting also, it specifies that batches be tested and mod roc motors be within 20% of the certified mean, and high power be within 10%.

7.8.6 Production lots shall be corrected, destroyed, or retested by the manufacturer under any of the following conditions:
(1) The total impulse of any model rocket motor or model rocket motor*reloading kit varies more than 20 percent, or any high power rocket motor or high power rocket motor*reloading kit varies more than 10 percent from the established mean total impulse value.
(2) The ejection charge, if any, of any test item does not function properly.
(3) Any test item malfunctions in any other manner that affects the safety of its shipment, storage, handling, or use.
(4) The time delay of any test item varies more than 1.5 seconds or 20 percent, whichever is greater, from the established mean time delay value of the rocket motor or motor*reloading kit. In no case shall this variation exceed 3 seconds
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  #64  
Old 06-27-2020, 05:30 PM
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My understanding is that a motor is kicked into the next impulse class even if the average total impulse is 0.01 N-sec over the limit for a class, regardless of the allowable standard deviation of total impulse in general. My understanding is also that the standard deviation requirement is more of a QC thing, to ensure that motors are relatively consistent with their certified total impulse.

Quote:
Originally Posted by Earl
Gary-

Thanks for taking the time to post here about Aerotech products; much appreciated.

On motors tested with NAR S&T (well, TRA too, I guess), what +/- on total impulse are you allowed for a given motor within an impulse class before it is ‘rejected’ as being out of spec? I assume it is some percentage level. Just curious....

Earl
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  #65  
Old 06-27-2020, 06:09 PM
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Default Thank you.

Many thanks to Mr. Rosenfield and everyone else who makes motors!

Otherwise....

Bob
p.s. what a pile of red tape and hoop jumping.
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  #66  
Old 06-27-2020, 08:02 PM
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+1 to what Bob just said above.
Mucho thanks to all those willing to wade through all the nuisance red-tape it takes to produce
commercial hobby rocket motors.
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  #67  
Old 09-03-2020, 02:41 PM
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I wonder if AT considered a 13mm A. They made a 13mm B7 for Apogee in the 90s. The B wouldn't fit in a standard length mini size case, but I bet an A would, and it would be fast burn so could set itself apart from Estes A3/10.
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  #68  
Old 09-03-2020, 05:59 PM
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We don’t believe the unit movement would justify the investment expense. Plus, there are extraordinary challenges in processing propellant in that diameter.

Quote:
Originally Posted by 5x7
I wonder if AT considered a 13mm A. They made a 13mm B7 for Apogee in the 90s. The B wouldn't fit in a standard length mini size case, but I bet an A would, and it would be fast burn so could set itself apart from Estes A3/10.
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For warranty questions & issues please contact Karl at warranty@aerotech-rocketry.com
For customer service questions & issues please contact Jenn at customerservice@aerotech-rocketry.com

AeroTech Consumer Aerospace
Division of RCS Rocket Motor Components, Inc.
2113 W 850 N
Cedar City, UT 84721
435-865-7100 (Ph)
435-865-7120 (Fax)
http://www.aerotech-quest.com
http://www.rocketmotorparts.com.com
http://www.specificimpulse.com
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  #69  
Old 09-03-2020, 06:06 PM
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Quote:
Originally Posted by AeroTech
We don’t believe the unit movement would justify the investment expense. Plus, there are extraordinary challenges in processing propellant in that diameter.


Good point, I hadn't considered that you were already producing 18 mm su and reloads so there was already a good foundation to build on there.

Thanks for responding, the topic of propellant and motor production is facinating to me.
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  #70  
Old 09-04-2020, 12:39 AM
Initiator001 Initiator001 is offline
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The back cover of the latest Sport Rocketry magazine (September-October 2020) features an AeroTech/Quest ad for the Quest Q-Jet motors. It specifically calls out the new White Lightning D20 motor which will be available for shipment this October.

Cool.
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