Measured motor delay thread

KennB said:

I hope no one is intimating any deviousness on the part of the vendors. That would be shortsighted as performance that varies from the published thrust curves and delay times would surely be reported on MESS forms and a motor would accumulate enough dings to bring it to S&T's attention. :wink:

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I wasn't implying any foul play, just that there should be testing of reloads that have sat around for a while in order to make sure that aging doesn't affect performance.

Winston said:

No deviousness, just that manufacturers certainly wouldn't take any LESS care in the manufacture of motors they send in for evaluation, right? On CATOs, I suspect that probably a minority are actually reported, especially in the case of single use motors, but that's just a hunch.

I'll change my original thread post to better reflect what I'm after. I suspect that even fewer long/short delays are reported than CATOs because people can often get away with them without damage to the rocket, as I did.

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CarVac said:

I wasn't implying any foul play, just that there should be testing of reloads that have sat around for a while in order to make sure that aging doesn't affect performance.

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Winston, I expect you're right that too few CATOs are reported and even fewer delay issues are written up. Whenever there is an event while I'm LCO, I remind the flyer to fill out a MESS report.

CarVac, you're right that some formulations don't age as well as others. Most of the time, that results in difficulty assembling the motor or igniting the propellant but may not make the performance vary more than is allowed. Lots of that information is either learned the hard way or passed down on forum threads and at launches. Again, budget and storage constraints prevent S&T from conducting such aging tests.

Thanks to those who have said kind words about the work that S&T does. When I joined S&T, I was working at a company that was submitting equipment to approval agencies and I wanted to see what life was like on the other side. It's really pretty interesting especially when a new motor is being developed and we get to keep secrets from everyone (until the manufacturer released the product). :tongue:

I can vouch for the older reloads in all flavors. In the pic. the "youngest" reloads left of what used to be a 164 reload stock pile(G's thru I's) are from 2005. Most were dated below that. I bought lots of reloads when Aerotech had a few problems years ago, fire, financial problems. Over the years I have bought other motors, sparkies, bigger, special need. Anyway I've been using these over the years, almost every one of them with the delays, including drilling when needed. Never had a problem until a few weeks ago. I had a G75-J with a very long delay. I drilled it from 10 to 8 seconds, but it was much longer.

I also went thru a few hundred single use motors,E's -G's Econojets as well as the standard G40's - 80's etc. Those were also used up from purchases years ago. Never had a delay problem with any, had 1 F20 and 1 G35 blow out the nozzles and that was it.

All the motors I've ever owned have been stored in a climate controlled room. They don't leave until they are ready for use. I hear of some people having lots of problems with cato's or delay swings one way or the other, In the past 18 years I just don't see it around here. I don't see it at club launches and the Rockets for Schools launches. All of the rockets used at Rockets for Schools are delay based ejections, Aerotech up until 2 years ago, and now CTI.

Winston said:

This is not meant to be data of certification accuracy or anything for certifiers to even be concerned about. This is BALLPARK stuff meant to find obviously long and short delays, like my 8 second Aerotech MPR motor delay that was 11 seconds long. The data's there, so lets use it, warts and all.

From my initial post here:

I realize they won't be perfectly accurate due to variables like motor temperature, chuffing, altimeters which use G forces to measure motor burnout (as I suspect they do; Gs can go negative before motor burnout), inadequate vent holes to accurately sense apogee, etc., but they'll be in the ballpark.

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A problem that the hobbyists have is that while the certification data is quite precise, it is based on less than a dozen static tests performed by the certifying authority on motors supplied by the manufacturer which are supposed to be typical production quality. NFPA 1125 places the day to day responsibility for motor quality and adherence to the certification parameters squarely on the manufacturer. The manufacturer is required to perform continual QA testing of their products and are required to modify or destroy production lots that do not meet the certification parameters, but there is no way to know what QA testing is performed or what corrective measures are being employed. You simply have to trust the manufacturer.

Bob

I believe that more people would report catos if they just knew how. We have a person in our group, that will show anyone how to report a cato if they just ask.

Andrew

Winston said:

No deviousness, just that manufacturers certainly wouldn't take any LESS care in the manufacture of motors they send in for evaluation, right?

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So you would think but all the manufacturers whose motors we've tested in the last 20 years have at least one fail to pass certification on the first try. I've always found this puzzling since they know what the test is ahead of time.

bobkrech said:

A problem that the hobbyists have is that while the certification data is quite precise, it is based on less than a dozen static tests performed by the certifying authority on motors supplied by the manufacturer which are supposed to be typical production quality. NFPA 1125 places the day to day responsibility for motor quality and adherence to the certification parameters squarely on the manufacturer. The manufacturer is required to perform continual QA testing of their products and are required to modify or destroy production lots that do not meet the certification parameters, but there is no way to know what QA testing is performed or what corrective measures are being employed. You simply have to trust the manufacturer.

Bob

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Yep, and that's why I'd like field data of significant outliers now that such info is more readily available due to wider ownership of altimeters like the Altimeter II.

billspad said:

So you would think but all the manufacturers whose motors we've tested in the last 20 years have at least one fail to pass certification on the first try. I've always found this puzzling since they know what the test is ahead of time.

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Great point. I never considered that.