Sanity check: OK that I assembled CTI 38mm a month before launch?

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rocketsam2016

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Inspired by the unopened before cert thread, I realized that I went ahead and assembled (though didn't drill the delay) my CTI 38mm L1 cert motor almost a month ago. At the time I wanted to just see how it felt, make sure I understood how everything (including aeropack retainer fit together), and have an accurate measurement of CG.

Now I'm second guessing myself - do I need to worry about flattening the O-rings? I thought about unscrewing it all but I don't remember how it came, and I don't want to get dust on the O-rings by unscrewing them and leaving them exposed - in the scuba world at least you worry just as much about dust as you do flattening for o ring seals.

Finally, holy cow CTI stock is low everywhere. Looks like I'm going to have to cert on the I236 I bought since my onsite vendor doesn't have 38mm Hs in stock that work for me.

Thanks for the help!
Sam
 

djs

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Motor should be ok- I've done this before myself.

if it's a 38mm motor, please make sure it's not in the date range where they are having some issues with the delay end/forward closure!

As far as it being the cert motor- it depends on your cert team. I've signed off on some L1 certs when they were CTI motors and already assembled. It's pretty easy to tell if they did it right or not. However, I'm not the one (most likely! :)) signing off on your cert.
 

timbucktoo

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I assembled my L1 motor at home and caught no grief then again it was an AT. Some people say yes, some no. Just depends on who certs your flight. I probably would have adjusted the delay grain before I assembled it too only because there is always the risk of crossing the threads on the 38mm rear closure. The fewer times you remove the rear closure, the better you are. I have had motors assembled for months with no ill-effect.
 

Banzai88

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I think the only real caveat is to keep them clean and dry. I've built up motors that I wanted to fly, and got rained out, and months later they lit just fine. I just store them in clean plastic bags with the caps on the nozzle.

Some folks, if they're not using them for a while will vacuum seal them in food saver bags.
 

Onebadhawk

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I built a Loki Research 76 / 6000 M 2550 LB for a fall MWP launch...
The launch was scrubbed due to weather...
The following spring at Red Glare in Maryland I scrubbed
because one of the altimeters was not doing what it should on power up...
The flight didn't go up until Airfest a month ago...
The motor was built for 11 months.....
During storage I did what I could to keep temp and more importantly humidity on an even keel...
Before the flight I pulled the O rings and regreased them.......
The motor lit and worked as it was supposed to....

Teddy
 

mccordmw

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It's a CTI, so there's not real assembly beyond sliding it in the case. Shouldn't cause an issue. When I received my CTI motor, you can bet that I opened it and checked to make sure it was in good shape and not one with a suspect forward delay closure. I wanted to make sure I had a good motor to bring to my cert., and had time to return it or get a new closure if there were issues.

APCP motors like what you have aren't as susceptible to moisture as something like an ANSU motor, so it should be fine. It's not a bad idea to toss it in a ziploc bag with the air removed to make sure moisture is controlled. Then again, I live in the moist sweatbox of MO, so I'm often battling the humidity; especially when painting. (stupid paint blushing...)

The TAP didn't care at all that I opened my motor package. I simply showed him the motor pulled out of the case and then firmly screwed in. He was more focused on the soundness of my build, how I planned to recover it, and then watching the whole flight.

So if you want to keep it in the case for now, I'd bag it and be prepared to pull it out to demonstrate that you didn't forget the liner and the closure/nozzle are well seated.

That being said, always check with that your NAR/TRA certifying lead thinks ahead of time.
 

jrkennedy2

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I think the binder ingredients in an APCP motor keep it in pretty good shape. The exposed surfaces can get a little "chalky" over many months but they seem to respond well to a little buffing down/rough-up the surface and they light fine. I guess all except some of the green formulas...??? I've been Ok with a 38mm built for 6 months and off she went at the press of "go".
 

Bat-mite

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I think some of you have misinterpreted the OP. He is not asking if the motor will retain integrity over time. He is asking if he is not going to be able to cert because he didn't build the motor in front of the cert witness. Thus, should he disassemble the motor and reassemble in front of witnesses. His concern is that if he does disassemble/reassemble, will that cause the motor to lose integrity due to dust, etc.?

So the answer is: talk to whomever will be signing your cert paperwork. If they are confident that you did build the motor yourself, and did it correctly, then they are likely to say, "Go ahead and launch."
 

rocketsam2016

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Thanks everyone! Indeed my question was multi-fold:

1) Is this going to be OK for cert purposes. It sounds like yes this is fine, and I'll drill the grain in front of the person too)
2) Now that I've assembled the motor a month ago, am I better off leaving it assembled (and therefore risking compressing/flattening the o-rings) or disassembling it but risking dust. It sounds like I should just leave it all assembled.
 

Bat-mite

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No, the answer is: don't assume any of those things. Talk to your cert team and get their okay. You can do whatever you want, but they can refuse to sign your application, too.
 

rocketsam2016

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OK I will. Again this is a CTI 38mm, so I'm happy to completely dissassemble and re-assemble in front of anyone who cares as many times as they want, and I bet I could do it blind folded :), but agreed I'll reach out ahead of time. My biggest concern was am I flattening the O-rings by leaving it assembled.

Thanks everyone for the quick thoughts.
 

Banzai88

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Of greater concern with the CTI 38s is buggering up the threads on the plastic rear closure, which can lead to unplanned and uncontrolled pyrotechnics on the pad. Popular practice is to assemble it one time only, carefully, and DO NOT over torque it into the case. If you have to, take it apart carefully and reassemble back into the case with a closer eye to not stripping the threads.
 

noffie79

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OK I will. Again this is a CTI 38mm, so I'm happy to completely dissassemble and re-assemble in front of anyone who cares as many times as they want, and I bet I could do it blind folded :), but agreed I'll reach out ahead of time. My biggest concern was am I flattening the O-rings by leaving it assembled.

Thanks everyone for the quick thoughts.
The O-rings will be fine if you leave it assembled. Good luck!
 

woferry

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You really don't want to cycle the threads on the aft closure of the CTI Pro38 any more than you absolutely have to (they're meant to go together once and then fly, the more you cycle them them more easily they can fail since they're just plastic against metal). So leave it together unless the person signing off asks you to disassemble it. I'd think anyone familiar with CTI motors would be able to easily inspect it from outside the case to confirm it was built properly, if the forward closure is sticking out the front and the aft closure threaded in the back and there seems to be propellant in the case you've done it right, the only other piece would be the liner itself and the O-rings, so just confirming you didn't take anything off that you shouldn't have would seem to cover it. If you're doing motor eject drilling the delay would be the only other thing to possibly check, but personally I'd talk that over ("show me how you did it") rather than ask to have the motor disassembled and risk doing more damage to the threads.
 

rocketsam2016

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Great, I've replaced one worry with another :)

How easy is it to tell if I've damaged the threads? I'm going to have to take it apart to drill the delay, so will it be obvious if I mucked them the first time?
 

timbucktoo

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It should screw in with very little if any force at all. If you feel any resistance, stop!
 

NateLowrie

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It should screw in with very little if any force at all. If you feel any resistance, stop!
This is how you tell. It should screw in with very little resistance. Hand tighten to a firm tightness but don't try to muscle it down. Don't overthink it either.

Have you checked the delay grain on the 38mm? CTI had a bad batch. Look to see if the plastic is shinier than the liner plastic. If it is, don't fly it and contact CTI for a replacement. If you need help telling, post a picture.
 

Bat-mite

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This is how you tell. It should screw in with very little resistance. Hand tighten to a firm tightness but don't try to muscle it down. Don't overthink it either.

Have you checked the delay grain on the 38mm? CTI had a bad batch. Look to see if the plastic is shinier than the liner plastic. If it is, don't fly it and contact CTI for a replacement. If you need help telling, post a picture.
Ditto. We had several rockets blown to smithereens last weekend because people didn't know about the forward closure issue. I took two of mine into AMW's trailer and got them replaced with brand-spanking-new ones.

I will no longer preassemble or drill Pro38 motors unless I have had the FC checked.
 

dshmel

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My standard practice is to assemble all motors (I fly mostly AT) in advance of a launch (so this may not be relevant to a cert flight). I do not tighten down the rear closure though, I screw it on just enough to have slight pressure on the 0-rings. I then tighten everything down at the launch right before inserting the motor into the rocket. This way, if I don't use a motor, it goes back into inventory. I also put the plastic nozzle cap on it (if the motor came with one) which seals up the motor to moisture and oxygen. This also means that I do not cut a vent hole or notch in the cap either (until right before launch). The only downside to leaving motors assembled is that you have a case tied up. But the alternative is a complete disassembly, which I don't like to do.
 

NateLowrie

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Ditto. We had several rockets blown to smithereens last weekend because people didn't know about the forward closure issue. I took two of mine into AMW's trailer and got them replaced with brand-spanking-new ones.

I will no longer preassemble or drill Pro38 motors unless I have had the FC checked.
We had 4 CATOs at the MDRA launch on Saturday. I don't know that all 4 of those CATOs were from the delay grain failures. I think the Der Red Max and the long gray one that landed on the grass were from bad delays as both got about 100 ft in the air before failure, but the other 2 never came up to enough pressure for any appreciable thrust and burned on the pad. All 4 had the forward closure failure but I doubt the latter 2 were due to bad CTI grains. The wall blowout on the bad CTI grains pretty much has to happen under pressure from what I understand.

Also, people knew about the forward closure issue. It was announced several times throughout the day and the AMW clue did a good job making sure people knew when they got 38mm motors from the trailer.
 

CORZERO

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Tripoli rules:

https://www.tripoli.org/Level1

"The flyer shall be observed by the certifying member or their designated representative during the assembly (if a reload or hybrid) and preparation of the motor."

NAR rules:

https://www.nar.org/high-power-rocketry-info/level-1-hpr-certification/

"The modeler must assemble the reloadable motor, if used, in the presence of a certification team member."

Because I'm a nice guy:

https://www.pro38.com/pdfs/Pro38_Case_Spacer.pdf

https://www.pro38.com/pdfs/Pro38Instns.pdf
 

CORZERO

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...do I need to worry about flattening the O-rings? I thought about unscrewing it all but I don't remember how it came, and I don't want to get dust on the O-rings by unscrewing them and leaving them exposed - in the scuba world at least you worry just as much about dust as you do flattening for o ring seals.
Flattening O-rings? Dust on O-rings? I'm not sure what this even means. Care to elucidate?

From a curious 15 year PADI Divemaster with more than a few first and second stage rebuilds under his belt.
 

ksaves2

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Tripoli rules:

https://www.tripoli.org/Level1

"The flyer shall be observed by the certifying member or their designated representative during the assembly (if a reload or hybrid) and preparation of the motor."

NAR rules:

https://www.nar.org/high-power-rocketry-info/level-1-hpr-certification/

"The modeler must assemble the reloadable motor, if used, in the presence of a certification team member."

Because I'm a nice guy:

https://www.pro38.com/pdfs/Pro38_Case_Spacer.pdf

https://www.pro38.com/pdfs/Pro38Instns.pdf
Good points/links. Fact of the matter is not all certifiers maintain the letter of the rule. I pre-assembled both my L1 and L2 motors off site and perhaps my prior reputation obviated the need for "observation".
Flew the attempts without issue. I hate to get greasy hands out in the field away from water and mechanics grade hand soap. Like many have posted, "Ask the certifier what they want."
I've been to some very busy launches where certification was going on and I hardly think someone was watching every motor assembly. By all means if the candidate wants to have a certifier watch
motor assembly, I don't think anyone will turn down their request of witness. Kurt
 

CORZERO

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Good points/links. Fact of the matter is not all certifiers maintain the letter of the rule.
Actually, the fact of the matter is that those are the rules. Should a prefect violate the rules and deviate from procedure is another issue. They flyer needs to understand the rules, not the 15 million interpretations he's getting from the rule-breakers.
 

timbucktoo

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Actually, the fact of the matter is that those are the rules. Should a prefect violate the rules and deviate from procedure is another issue. They flyer needs to understand the rules, not the 15 million interpretations he's getting from the rule-breakers.
Don't have to be a prefect to certify an L1 flyer.
 

CORZERO

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Don't have to be a prefect to certify an L1 flyer.
"Certifying member."

Certifications can be widely understood to occur during scheduled, insured prefect launches, therefore the word "prefect" was used. Thank you for playing.
 

watermelonman

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OK I will. Again this is a CTI 38mm, so I'm happy to completely dissassemble and re-assemble in front of anyone who cares as many times as they want, and I bet I could do it blind folded :), but agreed I'll reach out ahead of time. My biggest concern was am I flattening the O-rings by leaving it assembled.

Thanks everyone for the quick thoughts.
Do not worry about the O rings. Worry about the plastic threads.
 
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