CTI Discussion Thread

[Mike_Andrews]

Yeah, I kinda suspected that was the case. I've used CTI for several other launches with no issues. At least I got some really good data on this event. The rocket was completely 3d printed and it really showed me where I need to make some changes. All in all the rocket handled the impact better than I expected.

 

[ghostfather]

It looks like hot gas went out the side at the joint on the bottom of the motor.

If the nozzle failed, then grains could be moving downwards, causing that kind of flame melting the plastic casing between grains.
I've also seen this kind of damage from motors that weren't screwed up real tight after reassembly. The nozzle holder was only partially screwed in, so that when you shake the motor, you hear the grains rattle, meaning there is room between the grains. Sometimes it works, sometimes they CATO.
I think with this motor failure, it was the overpressure causing the nozzle to blow out, which may have resulted in the side flame and the delay not being lit, probably not a loosely assembled motor.

someone mentioned that maybe I missed applying grease?

That applies to Aerotech motors, it's not part of the CTI 38mm assembly instructions. I've never had to apply grease to CTI motors.

If the motor was within the first few years of manufacture (important to see the date stamp in the cardboard tube), the vendor should know that he can refund the motor, and will be reimbursed by CTI. I don't remember if it's 2 or 3 years after the manufacture date.

 

[Mike_Andrews]

Thanks! I was fairly certain I hadn't been told greasing was something I needed to do.

 

[crossfire]

Yes it looks like nozzle o ring let go. Maybe the o ring had a cut in it and split open when you slid reload in case.

 

[Cesaroni Technology]

Not sure if this is where to ask, but here goes.
I had a CATO today on the second flight of my rocket.

First flight was with an I180 Skidmark that was perfect (with the exception of the altimeter not actually recording the flight - bluetooth woes...).

Second flight was an I236 Blue Streak. Rocket ignited and then just off the rails went unstable and smashed into the playa. When I took a look at the motor the eject charge had not even fired. It looks like hot gas went out the side at the joint on the bottom of the motor. I did take the delay section out to dial back the delay charge. But other than that I didn't mess with the motor.

While I was at the local vendor table someone mentioned that maybe I missed applying grease? I don't remember having to do that before and I have flown CTI engines in the past where I adjusted the delay and didn't have any problems. Have I just been lucky or is this something that you don't do on the one shot motors?

Thanks,
Mike
(I'll have pictures up later once I am done showing the rocket debris to one of my friends...) :-/

Looks like a failure of the nozzle holder. Submit a warranty claim, we'll replace the reload and case.

 

[crossfire]

Yeah, I kinda suspected that was the case. I've used CTI for several other launches with no issues. At least I got some really good data on this event. The rocket was completely 3d printed and it really showed me where I need to make some changes. All in all the rocket handled the impact better than I expected.

Do you know if it was one of the motors that needed the pyrodex pellet trimmed?

 

[Charles_McG]

Do you know if it was one of the motors that needed the pyrodex pellet trimmed?

The pellet trim was only for the 38-1G. 2G if you were being cautious - especially the propellants with a narrow nozzle. The I236 is a 3G.

 

[crossfire]

Ok on the 3 grain. The same type failure I had was a 1 grain 38 motor. His Cato sounded a lot like the pellet issue.
See you at the Bong.

 

[Charles_McG]

See you at the Bong.

Looking forward to it. I've got more 2 stage sounding rockets to fly.

 

[Threemorewishes]

Here's my CTI wish list for your consideration.

Skidmark motors are fun but can sparks be added to other fuel types as an option?

Can delay grain smoke get an intense colour? Red? Orange? Black? The white/grey smokes can blend in with the clouds.

Are colour changing motors technically/economically feasible? Let's say it starts red and transitions to green or starts white and changes to Skidmark?

I will miss VMax motors. Any chance they could be made available every now and then? The I800 VMax is/was fun. A small run every two or three years would find instant demand.

I buy your competitor's single use motors for certain types of flights but would buy CTI if they were available. Any chance of this happening?

This would be a motor certification nightmare but a grain swapping matrix would be fun. Building a motor from loose grains of various fuels to make your own custom stack would be interesting. I know this is a pipe dream but one can fantasize.

Thanks for the opportunity to give some input.

Threemorewishes

 

[Cesaroni Technology]

Yes sparks could be added to any motor, though the sparky's really take a hit on performance. Might be an idea to ponder... We did try to make some coloured sparks, the results were less than satisfying.

I thought about doing different coloured smoke in the past, but from what I'm told the propellant burns too hot, the coloured particles lose their colour.

Colour changing propellants are possible, but it would be tedious to make them. A dual thrust motor could be made this way also.

We still have no plans for making VMax for the forseeable future.

We have made single use motors commercially in the past, we very well might make some for hobby use in the future.

Yes you're right, a grain swapping matrix would be a nightmare for certifying, but could maybe be used for EX launches, no cert required. I know someone who will take 2 different but same size motors and swap the grains between them, providing they both use the same nozzle throat.

Thanks for your input, it's greatly appreciated. It's nice to hear what ideas other people have.

Bob

 

[Bowman]

Yes you're right, a grain swapping matrix would be a nightmare for certifying, but could maybe be used for EX launches, no cert required. I know someone who will take 2 different but same size motors and swap the grains between them, providing they both use the same nozzle throat.

Am I misinterpreting something?
I don't believe swapping grains of certified motors meets the letter of the rule of TRA experimental (research).
Based on my interpretation that would disqualify the assembly from both certified and research flights.

Not saying that makes sense but it is not the spirit of EX.

 

[Cesaroni Technology]

Am I misinterpreting something?
I don't believe swapping grains of certified motors meets the letter of the rule of TRA experimental (research).
Based on my interpretation that would disqualify the assembly from both certified and research flights.

Not saying that makes sense but it is not the spirit of EX.

You're probably right, I just assumed if a motor isn't certified it could be flown at an EX launch.

 

[Titan II]

Am I misinterpreting something? I don't believe swapping grains of certified motors meets the letter of the rule of TRA experimental (research). Based on my interpretation that would disqualify the assembly from both certified and research flights. Not saying that makes sense but it is not the spirit of EX.

I see it as perfectly acceptable and I see no rule to preclude doing it. This is from the TRA website and has been brought up in previous discussions regarding this matter.

10. I want to ‘kit-bash’ some commercial motor parts to create a ‘custom’ motor. Is this allowed at a TRL? Yes, this is considered a Research motor. However, this is not allowed at non- TRLs since the motor is not certified.

 

[Jay Rairigh]

CTI must have known this! I most certainly did not. If three is magic number, why would you ever use more than three on anything with threads?

Please, nobody ever, EVER, use this 'rule'.
It is wrong in so many ways.
1st, an aerospace (or any) thread is allowed to be oversize for the 1st three threads!
2nd, generally you should have 1-2 times the diameter of the thread of engagement. In other words, a 1/4 screw would have between 1/4 and 1/2 engagement for max strength, depending on material.

If anything, the engineer was probably misquoted saying 3 times the thread diameter was wasted thread. Not 3 threads of engagement!

That's why most items have MORE than 3 threads of engagement.

Sorry, I just had to get that '3 thread rule' off my chest.

 

[Bowman]

I see it as perfectly acceptable and I see no rule to preclude doing it. This is from the TRA website and has been brought up in previous discussions regarding this matter.

10. I want to ‘kit-bash’ some commercial motor parts to create a ‘custom’ motor. Is this allowed at a TRL? Yes, this is considered a Research motor. However, this is not allowed at non- TRLs since the motor is not certified.

Real men cast their own grains.
Real researchers formulate them too, and define the operating pressure parameters and curve.
That's what I mean by the spirit of EX.

I said I did not necessarily think it made sense to preclude it, I just interpreted it as not included in the code.
Do what you want, where you want if it is allowed.
I won't call it my motor unless it truly is, cases being the exception in my book.

 

[Reinhard]

2nd, generally you should have 1-2 times the diameter of the thread of engagement. In other words, a 1/4 screw would have between 1/4 and 1/2 engagement for max strength, depending on material.

Note that this rule of thumb applies for your typical threaded fastener loaded in tension with "typical" proportions (e.g. UNC or ISO thread). CTI closures are different with trapezoidal threads and a comparably fine pitch in thin walled structures with rather low loads compared to their diameter. That's why a length of only 1/2" is appropriate for them.

Am I misinterpreting something?
I don't believe swapping grains of certified motors meets the letter of the rule of TRA experimental (research).
Based on my interpretation that would disqualify the assembly from both certified and research flights.

Not saying that makes sense but it is not the spirit of EX.

There was a time, when this was not allowed after the research codex got introduced. But this has changed since and maybe you still remember the old rules?

Real men cast their own grains.

Maybe it's less manly, but custom parts are certainly helpful for things like sub-minimum diameter rockets on commercial loads.


(the upper part gets glued into a coupler sized tube)

Reinhard

 

[Bowman]

Note that this rule of thumb applies for your typical threaded fastener loaded in tension with "typical" proportions (e.g. UNC or ISO thread). CTI closures are different with trapezoidal threads and a comparably fine pitch in thin walled structures with rather low loads compared to their diameter. That's why a length of only 1/2" is appropriate for them.


There was a time, when this was not allowed after the research codex got introduced. But this has changed since and maybe you still remember the old rules?


Maybe it's less manly, but custom parts are certainly helpful for things like sub-minimum diameter rockets on commercial loads.

View attachment 462720
(the upper part gets glued into a coupler sized tube)

Reinhard

Oh no argument on the custom parts sir. Ive made plenty of nozzles to fit different cases.

I am remembering the old code, a bit more conservative.
I reviewed the current code this afternoon and see Titan IIs point.
I stand corrected.

 

[Jay Rairigh]

closures are different with trapezoidal threads and a comparably fine pitch in thin walled structures with rather low loads

Totally agree. The CTI item pictured seems, and is probably tested, to be fully functional for it's purpose. I have made many threaded items like that in my lifetime.

 

[Zertyme]

So,
I've been trying to get the dimensions of an M2245 nozzle, but I can't find any information online or on your website. I've sent an email a week ago but I have yet to receive an answer. Is it possible to get dimensions such as the divergent angle, the exit diameter (not the nozzle OD of 2.200" shown on the Pro75_dimensions.pdf), and throat diameter?

Thank you.

 

[cbrarick]

So,
I've been trying to get the dimensions of an M2245 nozzle, but I can't find any information online or on your website. I've sent an email a week ago but I have yet to receive an answer. Is it possible to get dimensions such as the divergent angle, the exit diameter (not the nozzle OD of 2.200" shown on the Pro75_dimensions.pdf), and throat diameter?

Thank you.

gotta wonder why they would answer. Knowing throat size allows users to verify they got the correct nozzle.
What you ask allows for someone to clone their stuff.
That's not a good business decision.

 

[Zertyme]

gotta wonder why they would answer. Knowing throat size allows users to verify they got the correct nozzle.
What you ask allows for someone to clone their stuff.
That's not a good business decision.

I need to know the dimensions of the nozzle for one reason. Because I'm working on a two-stage N5800 to M2245...
Anyway...

 

[3stoogesrocketry]

I need to know the dimensions of the nozzle for one reason. Because I'm working on a two-stage N5800 to M2245...
Anyway...

For a project of this magnitude , and from the sounds of your interstage , I would suggest purchasing a nozzle from your vendor or the complete motor now. It would suck to build a mating plug to stack the motor on to have the angle be slightly off.

 

[Zertyme]

For a project of this magnitude , and from the sounds of your interstage , I would suggest purchasing a nozzle from your vendor or the complete motor now. It would suck to build a mating plug to stack the motor on to have the angle be slightly off.

Indeed, purchasing the motor was my backup option.

 

[crossfire]

Hi CTI
I had a warranty claim awhile back which you replaced a 38mm 1 grain case and reload. I was going to use the case last week for the 1st time since you replaced it. When removing case from the plastic tube for the 1st time case looks used. Upon trying to put reload in the case the reload will only slide in about half way. Put same reload in a 2 grain case with spacer it works perfect. Sticker on case has a lot of the writing wore off and threads even had some curd in them.

 

[Reinhard]

gotta wonder why they would answer. Knowing throat size allows users to verify they got the correct nozzle.
What you ask allows for someone to clone their stuff.
That's not a good business decision.

It depends very much on what is asked for. Some things fall very much in the secret sauce category (e.g. propellant formulation). Other things can be easily reverse engineered by everybody who buys their product. No competent competitor will be appreciably helped by what has been asked, so it doesn't hurt to ask.

Back in 2015 I asked Jeroen nicely about some non-public information about their V2 casings. Pro 75 V2 was available then, but Pro 98 V2 wasn't even announced and we needed a spec detail and confirmation that the HW was in the works. V2 was preferred, because the integrated thrust ring of V1 would have been rather inconvenient. Thankfully, he shared with me the information and that the HW would be available in time.

Turns out, the machinist was not familiar with that particular spec and ended up reverse engineering / fitting the parts anyways (the HW was available by the time we were ready for manufacturing), but Jeroens information was still very helpful for our planing and design. So far we spent around 10k on CTI products alone for that project, which interestingly uses exactly the same motor configuration as Zertyme's project.

Reinhard

 

[Cesaroni Technology]

So,
I've been trying to get the dimensions of an M2245 nozzle, but I can't find any information online or on your website. I've sent an email a week ago but I have yet to receive an answer. Is it possible to get dimensions such as the divergent angle, the exit diameter (not the nozzle OD of 2.200" shown on the Pro75_dimensions.pdf), and throat diameter?

Thank you.

We haven't received any emails regarding your inquiry. Where did you send the email to?

 

[crossfire]

CTI did you see my post on the warranty 1 grain 38mm case?

 

[crossfire]

CTI
I sent picture off tight case to you by private message.
Thanks

 

[scschulte]

Yes sparks could be added to any motor, though the sparky's really take a hit on performance. Might be an idea to ponder... We did try to make some coloured sparks, the results were less than satisfying.

I thought about doing different coloured smoke in the past, but from what I'm told the propellant burns too hot, the coloured particles lose their colour.

Colour changing propellants are possible, but it would be tedious to make them. A dual thrust motor could be made this way also.

We still have no plans for making VMax for the forseeable future.

We have made single use motors commercially in the past, we very well might make some for hobby use in the future.

Yes you're right, a grain swapping matrix would be a nightmare for certifying, but could maybe be used for EX launches, no cert required. I know someone who will take 2 different but same size motors and swap the grains between them, providing they both use the same nozzle throat.

Thanks for your input, it's greatly appreciated. It's nice to hear what ideas other people have.

Bob

Hello -- This is not 100% on topic but I think close. Yesterday launching my MadCow "Dutch Frenzy" in The Netherlands I used a 38 mm CTI 434 I223-14A SkidMark. I've used these excellent motors for years-- but it seems that since my last Skidmark flights in the USA in 2016 and 2017 using these motors and the recent flights 2020 and 2021 the "spark" has gone from these motors. See the pictures attached -- the pics with the HUGE amount of sparks are from 2016-17 (Belgian Flag painted Black-Yellow-Red Endeavour) and the Blue-white-red rocket shows "some sparks" but it seems almost like a "classic" burn motor-- not a "true SkidMark". I am wondering if the formulation has changed for the Skidmarks? The 2016-17 motors had production dates about 2014-2016 and the recent low-spark ones 6 June 2019. Be great to hear your feedback! The motors all worked great from an ignition, thrust and overall reliability standpoint. Dual deploy -- great flights. Thanks, Stephen Monday 24 May 2021