CTI Discussion Thread

[manixFan]

If you actually read my post, you will see I only addressed the issue of CTI supplying an extra O-ring. I never mentioned epoxy.

I actually did read your post which is why I replied. While you did quote the two-o-rings, it seemed you may have been also speaking more generally about the issue. FWIW, several in our club also add the extra o-ring, but I think I recall the older closures did not have two grooves, so it’s a somewhat more recent development.

Sorry about my overly broad interpretation of your statement.

Tony

 

[rfjustin]

If you actually read my post, you will see I only addressed the issue of CTI supplying an extra O-ring. I never mentioned epoxy.

Sorry, but part of your question posed was, "Based on what?" and @manixFan's answer to said question was vendor recommendation and empirical data from other fliers. Not sure why your being so critical of the feedback when it was in response to your own inquiry...

 

[crossfire]

Not sure if this has been mentioned but are flyers seeing failures when useing a grain spacer?

 

[JimJarvis50]

I have flown many CTI 6-XL motors, mostly L265 and L935 and have never had an issue, however I started gluing my closures in several years ago. However, I have personally witnessed many such failures, including 2 from our group at Airfest last year. The failure mode is almost always the same - a gas leak right below the forward closure. I have been using epoxy on my longer CTI motors for several years - based on both the recommendation of my motor vendor and several other well-known flyers who experienced the problem. It’s far more than just a couple of people, and you ignore the advice at your own peril.


Tony

”the space shuttle survived many foam strikes until it didn’t”

Just to clarify, the issue with the 54's is not the larger O rings around the closure, but rather, the interface between the closure and the liner. The failures are at the bottom of the closure. I suspect I'm the one that started this practise many years back - 2015 maybe? I glue the closure on all reloads and have not had a problem since I started doing it. I have, however, seen the problem happen on motors that had been glued. Not very often, but it has happened. We need a better fix.

Jim

 

[crossfire]

So do you make sure to keep glue off the o-ring? I would think so

 

[JimJarvis50]

So do you make sure to keep glue off the o-ring? I would think so

No. I glue the entire assembly. I can see the case for not gluing the O ring, but it's not what I do. I'm trying to keep the closure from moving relative to the liner. So, I'm trying to glue as much of the closure to the liner as possible. YMMV

Jim

 

[Rocketjunkie]

Just curious, why not Viton? Buna-N better for some reason? Viton temp just not needed? Doesn't matter?

Buna-N is a LOT cheaper. Since the o-rings are discarded after flight, there is no need for the 'better' O-rings. Viton is also much easier to nick, breaking the seal.

 

[OZRoc]

Anybody have any difficulty with 75mm liners jamming in the casing? Had one bind up on me last week and can't get it out. Will have to make up a pull/pusher to get it to budge.
Cheers and TIA,
Mark

 

[mikec]

Anybody have any difficulty with 75mm liners jamming in the casing?

Did it go in OK and was just hard to remove, or was it tight from the start? I had a terrible experience a few days ago which I recounted a couple of pages ago in this thread. It seems that CTI is having trouble making liners within spec lately.

 

[Cameron Anderson]

Anybody have any difficulty with 75mm liners jamming in the casing? Had one bind up on me last week and can't get it out. Will have to make up a pull/pusher to get it to budge.
Cheers and TIA,
Mark

I had one that would NOT go in...M840 last year. Eventually it cracked lengthwise the entire length of the case. I even tried sanding it when I first has an issue, didn't work.

 

[OZRoc]

Did it go in OK and was just hard to remove, or was it tight from the start? I had a terrible experience a few days ago which I recounted a couple of pages ago in this thread. It seems that CTI is having trouble making liners within spec lately.

I had one that would NOT go in...M840 last year. Eventually it cracked lengthwise the entire length of the case. I even tried sanding it when I first has an issue, didn't work.

Interesting..... I flew another (L820 SK) a couple of months ago no problem at all. This one (L645 GR) would go in only approx half way before binding. Pushed a bit too hard now it's jammed. These are CTI 3G reloads in CTI 4G case.
Cheers

 

[mikec]

Pushed a bit too hard now it's jammed.

I used a 2-inch wood post and an AT seal disk to push/pound it out. The liner seems to have survived but I'm a little nervous about it. Cameron, did they replace your cracked liner?

 

[crossfire]

With these tight liners. Do the grains slid in the liner or are they very tight in liner. Is the case out of specafation or is it the liner?

 

[Rocketjunkie]

AT/CTI 75 mm liners 2.625" ID, 2.730" OD. ID is mandrel size and usually very close. OD is ground and can vary quite a bit. These are standard tolerances Has your motor case had a rough flight? Make sure the case is not flattened.

 

[DaHabes]

On the surface it seems like CTI reloads are a lot easier to use than Aerotech, but if the quality control isn't there and people are having to resort to practices (epoxy) that aren't a part of the manufacturers procedures, I think I'll avoid CTI if I decide to expand beyond AT DMS. This has been going on for years? In a hobby like HPR that can be dangerous, I find it puzzling why the governing bodies that certify motors haven't put the screws to CTI. I would think if you de-certify problematic motors and/or specific reload designs (54mm), they would get their **** together post haste. Personally, since safety is a primary mission of TRA and NAR, and they provide the insurance for the clubs to be able to fly without undue risk, I'm really surprised this hasn't been addressed formally.

 

[mikec]

AT/CTI 75 mm liners 2.625" ID, 2.730" OD. ID is mandrel size and usually very close.

My case has been used many times with both CTI and AT reloads and has never had a problem with fit, is pretty clean, and not damaged. So I'm blaming the liner. The grains were tight in the liner and the whole assembly didn't fit in the case.

 

[OZRoc]

Just finished removing the liner. Heated the case up over a column oil heater then did as @mikec did with the post & AT seal disk. Came out fairly easy. Cleaned everything up and did some measuring. The liner in question is definitely larger at one end. Noticed also that the nozzle was taped into the liner (presumably for transport) whereas the nozzle for the 820 SK was not. (Very tightly held in the liner). Also tried another liner for an L1350 CS. It only pushes in approx 4" either end then jams. It's nozzle is also taped in (loose in the liner)
Am hoping CTI will jump in here and suggest a solution. Don't really want to go the warranty way but will if necessary. Also don't want to randomly sand down the liners.
Cheers.

 

[crossfire]

Hi Robert from CTI did you get my last message?

 

[mikec]

I find it puzzling why the governing bodies that certify motors haven't put the screws to CTI. I would think if you de-certify problematic motors and/or specific reload designs (54mm), they would get their **** together post haste.

Either that or they would simply exit the hobby market. I have no idea what fraction that is for CTI, but it might not be that much.

At any rate, these problems mostly fall short of being major safety issues (NAR/TRA did ban the flying of Vmax without electronics when the delays became unreliable), but they are certainly extremely irritating. I'm voting with my wallet, it's about all we can do.

 

[Tim51]

Two great flights on CTI motors at my club's two day event at the weekend:
5643' on a J760 - my first time using this particular motor and a very cool flight:



Then an I285 for a low motor eject flight with a 5.54" airframe:



Pictures courtesy Pete B / H.A.R.T. Rockets.

 

[Dudeman247.]

Had my first flight over 10k on a K-260. What a great motor!

 

[JohnCoker]

What is the recommended minimum length of time delay grains should be adjusted to? There are various suggestions that too short is unsafe, but we haven't been able to find an official statement.

This came from a thread about delay adjustment in general.

 

[crossfire]

Just want to thank Bob at CTI for sending me out a 38mm case which was a warranty claim.

 

[Rocketjunkie]

CTI also fixed my closure problem with an older one. I can fly my 3-54mm cluster again (After loaning my 54-4g case and closure to a SLI team. Then COVID hit and we lost contact. Had to order a new 54-4g case and closure. Mentioned earlier in this thread.

 

[JohnCoker]

Note that all available delays are listed with the motor on the CTI site. For example: http://pro38.com/products/pro24/motor.php

 

[BF Rockets]

Anybody have any difficulty with 75mm liners jamming in the casing? Had one bind up on me last week and can't get it out. Will have to make up a pull/pusher to get it to budge.
Cheers and TIA,
Mark

I have 3 75mm CTI motors in my stash and all of them had this problem. Two M2245s and a 2 grain VMax (K2000?). If you want a workout, the remedy is to use coarse sandpaper like an 80 grit and go to work on the liner. I have a gen 1 and a gen 2 6XL case and the fit of both M2245 liners was the same in each case - the liner would go in about halfway and get stuck.

 

[crossfire]

Just curious how dose the liners fit it Aerotech style hardwear?

 

[BF Rockets]

Just curious how dose the liners fit it Aerotech style hardwear?

The liners don't fit in the AT cases I have either. AT liners I have slide right through the CTI cases without a problem.

 

[Ulexis]

Does anyone besides me think its odd CTI hasn’t responded to anything on this thread for almost 2 months?

 

[crossfire]

The liners don't fit in the AT cases I have either. AT liners I have slide right through the CTI cases without a problem.

Will CTI grains slid in AT liners?