Any tips for CTI 38mm pro motors?

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Off Grid Gecko

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Looks like the weather is going to be okay this month. Hopefully I'll be launching my L1 Saturday or Sunday at Walnut Grove Missouri. Little nervous.
I need to do a full run-through of my aircraft again and make sure that I'm an expert on all the questions that might get asked at the RSO table, and was thinking about my motor.
The Pro38 doesn't have a rear closure. This is the procedure in my head:
Open the bag.
Remove the delay block at the front and drill out the charge to the right setting with ProDAT tool. I've seen some vids of this. Then reinstall.
Screw assembly into Pro38 case.
Load into rocket, straighten ematch but don't install till on the launchpad.

I've seen some posts about epoxy and stuff on bigger motors. Is there anything I need to do extra or worry about with a 3-grain 38mm CTI motor? Just want to make sure that I don't do anything dumb. I can't assemble it till I get there so someone can witness it.
 

timbucktoo

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You got it right. No glue recommendations for the 38mm motors. Sometimes I use a light spray of silicon to aid in inserting the liner. Take your time when screwing the aft closure too. Can be cross threaded if not careful.
 

HHaase

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It may sound silly, but you'd be surprised how often people CATO by accidentally stuffing the reload into the rocket without the case. Always verify it's actually got the casing.

With composites, there is a delay between hitting the button and the motor coming up to pressure. This is normal. Though not as pronounced on CTI's in this size due to the black powder pellet used to improve ignition.

If it doesn't fire, do NOT go right up to the pad to check on things. A hang-fire on a composite can light off unexpectedly if there's still an ember or other hot spot in there.

Which brings up another point. You shouldn't need to handle the grains separately. If you do then, keep track of which one goes up top near the delay, it's the one with the ignition pellet.
 

JimJarvis50

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Yep, be careful about cross threading. I turn the closure in the opposite direction until I hear the threads "click", and then I screw in the closure. Don't use any force doing this. If the threads are oriented properly, it won't take any force to screw it in.

And be sure to actually use the case! Although I've never done it, many people have inserted the reload in the rocket without the case. They become members of the "hall of flame" club.

Jim
 

Titan II

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This is a previous post regarding lube.....


Jeroen_at_CTI Jeroen_at_CTI is offline
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Quote Originally Posted by CarVac View Post
What sort of spray?
A "Silicone Spray". If you Google that, you will find lots of options. It does not build up. It is very thin. Some examples:
- Permatex 80070
- Liquid Wrench M914
- WD-40 Specialist Silicone Lubricant (note: not regular WD40).

Jeroen

If you do not know, Jerone is Mr. CTI

I use this and all loads slide in, and thread in, easily.
images (13).jpg
 

ThirstyBarbarian

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They are super easy to use, and you outlined the steps exactly correctly.

I haven’t used the spray lube myself, but I plan to start, and the way you use it is to spray the interior of the metal casing so the reload can slide in easily, and any burnt residue will be easy to clean out. It’s really optional, and you don’t need anything more than a very light spray. Don’t get lube on the propellant grains inside the plastic liner, especially do not contaminate the delay grain with any kind of grease that could inhibit it from lighting.

CTI igniters for most of their motors are just an ematch with no pyrogen, so don’t be worried if it looks different from igniters you are used to. It doesn’t need pyrogen because the motor has a pyrodex pellet built into the forward end to light the propellant grains. That means the igniter needs to be in contact with that pellet. When you insert the igniter, be sure it goes all the way up to the forward end of the motor, and you feel it make contact. When it’s in contact, make a small zigzag bend or little loop in the igniter right at the nozzle. Insert the leads end of the igniter into the open side of the yellow plastic nozzle cap and run the leads out the hole in the side of the cap. Then slide the yellow cap up the igniter and press it into place on the nozzle. The zigzag can’t easily pass through the hole in the yellow cap so it keeps the igniter from sliding out of position and keeps the hot end of the igniter firmly against the pellet in the forward end of the motor.

People aren’t joking about forgetting the casing! I’ve seen it more than once, and I actually almost did it myself once! It only happens with CTI 38mm, and it’s because the motor’s thrust ring is built right into the aft closure and nozzle piece. For any other type of motor, the reload needs to be in the case and the closure screwed on in order to have a thrust ring, so the same mistake is impossible, because you would immediately notice there was no thrust ring when you went to put on your motor retention. You won’t forget, but it’s good to have a reminder.

What motor are you using, and what is your ideal delay?
 

Adam3836

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Looks like the weather is going to be okay this month. Hopefully I'll be launching my L1 Saturday or Sunday at Walnut Grove Missouri. Little nervous.
I need to do a full run-through of my aircraft again and make sure that I'm an expert on all the questions that might get asked at the RSO table, and was thinking about my motor.
The Pro38 doesn't have a rear closure. This is the procedure in my head:
Open the bag.
Remove the delay block at the front and drill out the charge to the right setting with ProDAT tool. I've seen some vids of this. Then reinstall.
Screw assembly into Pro38 case.
Load into rocket, straighten ematch but don't install till on the launchpad.

I've seen some posts about epoxy and stuff on bigger motors. Is there anything I need to do extra or worry about with a 3-grain 38mm CTI motor? Just want to make sure that I don't do anything dumb. I can't assemble it till I get there so someone can witness it.
Good luck you got this !!
 

boatgeek

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After you drill the delay, clean any cut up delay material from the hole and touch it up one more time with the delay tool. A nice clean hole has a more accurate delay.

I like to do a few things with the igniter:
Split the leads on the igniter at your prep table and tape it to your rocket. You can't forget it at your prep table if it's taped on!
After you do the Z-fold like Thirsty said, pull the igniter out and make sure it's about the length you expect it to be.

You've got this! Good luck!
 

Off Grid Gecko

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Yep, be careful about cross threading. I turn the closure in the opposite direction until I hear the threads "click", and then I screw in the closure. Don't use any force doing this. If the threads are oriented properly, it won't take any force to screw it in.

And be sure to actually use the case! Although I've never done it, many people have inserted the reload in the rocket without the case. They become members of the "hall of flame" club.

Jim
Oh for sure. Coming from oilfield stuff we would often reverse spin brass battery retainers until they "seated" in their groove, then spin them up and torque together. Every single time. I even do it with difficult steel nuts sometimes. Great safety point. I'll remember to do it.
 

Off Grid Gecko

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I didn't expect THAT many warnings about loading without a case, but suspected someone might mention it. Seen a YT vid where a rocket burned down on the launchpad instead of going up, thanks to no case. I'd like to think I wouldn't make that mistake, as I'm pretty cautious when it comes to explody things like rockets and ammunition, but maybe I'll put some masking tape over the MMT as a reminder (like a string tied on the finger). Might even write on it. "Got Case?"
Thank you all for the insights. I don't think I have any spray lube around here anywhere, so I might bypass that step this time if I can't locate some. Will look next time I'm in town. I'd sub some sunflower oil, but don't want to take the risk of it polymerizing inside the casing, though that would leave a nice non-stick surface if you could scrape the burnt plastic off, lol.
Thanks again everyone. Been looking forward to this for a couple years so I'm kinda amped about finally doing it.
 

Off Grid Gecko

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What motor are you using, and what is your ideal delay?
It's an I-175 with a 14s fuse. I plan on drilling it to 11s (-3). OpenRocket says 10.8 for optimum. Was 9 but I added a lipo to the payload bay to increase the stability a bit. It was getting close to 1.5 cal and I wanted some wiggle room when the RSO asks. (I assume they ask about these things)
Anyway, I guess the added weight increased the sectional density enough to make it push a little higher and have a longer coast.

edit: changed "1 cal" to "1.5 cal"
 

o1d_dude

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No worries.

Don’t make a big deal out of it. Just take your time and do what you know to do.

I suspect you’ll get it right on the first try.

Then celebrate your success.
 

Off Grid Gecko

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10+mph winds all day predicted now...........
I don't like that. Guess I'll see what everyone is flying and maybe try one of my LPRs to gauge how bad that's going to carry a rocket. Might need to borrow a smaller chute.
 

jd2cylman

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If you have the 38mm spacers, use the spacer to fully seat the reload into the case, then install the aft closure/nozzle/nut. That way the threads on the nozzle are only pushing the aft o-ring into the liner and not trying to push the whole reload further into the case.
 

Off Grid Gecko

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If you have the 38mm spacers, use the spacer to fully seat the reload into the case, then install the aft closure/nozzle/nut. That way the threads on the nozzle are only pushing the aft o-ring into the liner and not trying to push the whole reload further into the case.
Interesting... Took me a couple of reads but I think I get what you are saying. I don't have any spacers yet, but I could prolly accomplish the same (assuming it's a pretty good fit) by threading only a couple of turns, then insert snugly into the aluminum case, then tighten the rest of the way down. Sounds like the same kind of philosophy?

EDIT: wait, it's an oring fit for the reload part, so maybe loosed the nozzle end... I don't know, I'm not getting a clear picture of this in my head yet. I'll think on it more.
 

jd2cylman

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Use the cut edge of the spacer to push on the cut edge of the liner.
I don't have any spacers yet either since the set I bought had every case. The 38mm 1 grain case is a stubby lil thing...
Trying to remember if I've flown any 38mm CTI... Hmm I think a couple. I have a couple of 5 or 6 grain reloads to use.
 

Off Grid Gecko

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Use the cut edge of the spacer to push on the cut edge of the liner.
I don't have any spacers yet either since the set I bought had every case. the 38mm 1 grain case is a stubby lil thing...
Trying to remember if I've flown any 38mm CTI... Hmm I think a couple. I have a couple of 5 or 6 grain reloads to use.
Hehe. yeah. I got my case as part of the L1 special. I hate to admit it, but that's one reason I went with a 3G motor instead of 2G, and I was pretty confident. Still am, just nervous about the launch, new people, the weather gods, etc. Next motor purchase I plan to order several G's and H's and two spacers to complete my little "kit."
 

Rocketjunkie

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Aerotech seal disk or even the fiber washer from a smaller Aerotech reload will work to push in the nozzleless reload.
 

ThirstyBarbarian

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I’ve never done the spacer thing, and I’ve never seen anyone else do it or anything like it. I think it’s better to just leave the reload assembled and slide the whole thing in as a unit and tighten the closure. You don’t want to screw up the end of the liner pushing on it with things.
 

ThirstyBarbarian

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It's an I-175 with a 14s fuse. I plan on drilling it to 11s (-3). OpenRocket says 10.8 for optimum. Was 9 but I added a lipo to the payload bay to increase the stability a bit. It was getting close to 1.5 cal and I wanted some wiggle room when the RSO asks. (I assume they ask about these things)
Anyway, I guess the added weight increased the sectional density enough to make it push a little higher and have a longer coast.

edit: changed "1 cal" to "1.5 cal"
Perfect. It sounds like you have it figured out very well. Good luck on your cert flight!
 

markjos

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I’ve never done the spacer thing, and I’ve never seen anyone else do it or anything like it. I think it’s better to just leave the reload assembled and slide the whole thing in as a unit and tighten the closure. You don’t want to screw up the end of the liner pushing on it with things.
Yes, if it goes all the way in, smoothly. I think what's being referred to, and something I've certainly experienced with a Pro38 reload, is difficulty with the last 1/8" or so of insertion, and then risking stripping the closure threads trying to get it home (to close the remaining gap). Sometimes, being able to press the assembly against a hard surface, without the nozzle and aft closure in place, has been really helpful.
 

rharshberger

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You got it right. No glue recommendations for the 38mm motors. Sometimes I use a light spray of silicon to aid in inserting the liner. Take your time when screwing the aft closure too. Can be cross threaded if not careful.
+1, and 38mm are the only size with plastic rear closures, easy to cross thread.
 

Off Grid Gecko

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What about tension? It'll have a screw on retainer ring holding it inside the rocket. Just snug it up finger tight when installing it?
 

Off Grid Gecko

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Snug it down hand tight, it will be okay.
Just came to me that it might be one of those things that can be easily over-tightened and then never want to come out again. I might not even try to take it out until I get her home, but then again, someone might talk me into buying another motor for it on site.
Had a similar "doh" moment this evening as well with one of my smaller rockets. I wasn't going to take it because my last order with the D motors hasn't come in yet, but then it occured to me that I plan on leaving early and there's a Hobby Lobby right there in Springfield. Might drop by and grab some D's and E's. If the wind forcast is accurate, I'm going to serious contemplate scrubbing my L1 for another date. Now saying 13-14mph all afternoon and it's a 3000ft flight plan. Course, I will elicit the wisdom of the club members who fly the field regularly. They would know where the rockets like to go. I don't mind walking, but don't want to walk a mile and then find her floating in the middle of a cattle tank or something like that.
 

JimJarvis50

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Yes, if it goes all the way in, smoothly. I think what's being referred to, and something I've certainly experienced with a Pro38 reload, is difficulty with the last 1/8" or so of insertion, and then risking stripping the closure threads trying to get it home (to close the remaining gap). Sometimes, being able to press the assembly against a hard surface, without the nozzle and aft closure in place, has been really helpful.
Yes, yes! I don't fly many 38mm motors, but now I remember that I got a spacer specifically for the purpose of getting the reload completely inserted. Without a spacer, you have to try and push in the liner with your thumb nails. Sometimes this works and sometimes not. But it you don't get that last 1/8" into the case, the closure won't screw on. Watch for this - it's common.

Jim
 

Off Grid Gecko

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Yes, yes! I don't fly many 38mm motors, but now I remember that I got a spacer specifically for the purpose of getting the reload completely inserted. Without a spacer, you have to try and push in the liner with your thumb nails. Sometimes this works and sometimes not. But it you don't get that last 1/8" into the case, the closure won't screw on. Watch for this - it's common.

Jim
couldn't resist. I Took the reload out of the pink bag for a minute and did a test fit. Slides in really easy. Stuffed it back in the bag and taped it up. I've seen people saying they will open their motors and leave them in the rocket for years, but I like keeping things as fresh as possible. Sort of had to know so I could bring something along to stuff it in there if needed, but luckily not needed.
 

ThirstyBarbarian

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I guess I’ve never run into this problem with the 38mm motors where you have to push the liner in. Mine have always just slid right in up to the threads, and then I just tighten it down. Well, I guess I’ll know what to do if it ever doesn’t slide all the way in — push the liner in with a spacer. Learn something new every day!
 

o1d_dude

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I have a particular Cesaroni case that refuses to accept an I195(?) reload. Ended up buying a replacement case and the reloads drop right in. There are NO dents, warps, or damage to the original case. Even Dr. J (Jeroen) was puzzled.

I now know why the original owner sold the case cheap. Good for use as a bong, perhaps.
 

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