Aero Pack 54mm tool less mount not compatible with CTI engine case?

[bchaltraw]

I was just prepping to install my Aero Pack quick engine mount in a 54mm rocket. I just bought a CTI reload kit and the CTI tube will not slide into the Aero Pack. 54mm should be 54mm, but are these really not compatible? I have two Aero Packs and the same problem with both. Motor fits in the motor mount just fine. Should I file/sand to get them to work? For the premium cost surprised the tolerances are off.

 

[rfjustin]

I was just prepping to install my Aero Pack quick engine mount in a 54mm rocket. I just bought a CTI reload kit and the CTI tube will not slide into the Aero Pack. 54mm should be 54mm, but are these really not compatible? I have two Aero Packs and same problem with both. Motor fits in the motor mount just fine. Should I file/sand to get them to work? For the premium these cost surprised they tolerances are off.

Got a dial caliper handy? What is the measured ID of the flange mount 54mm please?

I have a flange mount 54mm downstairs and will measure it soon and post the results for you.

Best,

 

[rfjustin]

I was just prepping to install my Aero Pack quick engine mount in a 54mm rocket. I just bought a CTI reload kit and the CTI tube will not slide into the Aero Pack. 54mm should be 54mm, but are these really not compatible? I have two Aero Packs and same problem with both. Motor fits in the motor mount just fine. Should I file/sand to get them to work? For the premium these cost surprised they tolerances are off.

Also, do you have a different 54mm case you can try to fit? You may have an out of spec 54mm case on your hands.

 

[crossfire]

Dose a rear clouse screw on to the case?

 

[Banzai88]

 

[Steve Shannon]

I use CTI hardware with Aeropack retainers all the time, so something is wrong with your individual setup. It could be any of three different things, or a combination of things:
1. Problems with the CTI hardware - measure it or try a different set,
2. Problems with the Aeropack - measure it per rfjustin’s suggestion,
3. You have an issue with the motor mount tube (MMT). This is by far the most common issue I’ve seen. In fact I’ve never seen an issue with #1 or #2 above, but that doesn’t mean it can’t happen. Just one drip of epoxy in the MMT can make it seem as though there are problems with the hardware. I don’t ever epoxy on the retainer without test fitting the motor hardware first, and I usually have the motor in place when I epoxy the retainer to the MMT just to prevent getting it off center. Fortunately, if it is a problem with the motor mount tube, it’s more easily rectified. Just scrape out whatever is interfering.

Edit: disregard #3; I see that you are test fitting without the MMT installed. You definitely have a problem with either 1 or 2. Do you have another motor to test fit?

 

[rfjustin]

@bchaltraw, I have (2) of these retainers at home, one installed, one new in package not touched until now. Critical measurement on both of mine are 2.144" exactly. I would bet money your CTI motor case is greater than 2.125" OD. BTW, OD of AT 1706 case I am holding measured 2.1245".

Best,

 

[bchaltraw]

Just pulled out a second tube, same problem 54MM CTI 3G and 6G neither will fit. So got out the Calipers, CTI 2.125, and Aero 2.118 on both of the mounts.

 

[Banzai88]

Just pulled out a second tube, same problem 54MM CTI 3G and 6G neither will fit. So got out the Calipers, CTI 2.125, and Aero 2.118 on both of the mounts.

Well, there you have it!

Sounds like it's time to attach these pictures to an email to the vendor or directly to AeroPack/MadCow.

 

[crossfire]

Looks like MC has a little problem. How long ago did you get the retainer?

 

[bchaltraw]

I just bought them on the Black Friday sale from Mad Cow, One is already mounted in the rocket, and the other one I have in hand. I could get bust out some Emory cloth and make an adjustment. For $41 each very surprised they had tool creep but it is what it is.

 

[Banzai88]

I just bought them on the Black Friday sale from Mad Cow, One is already mounted in the rocket, and the other one I have in hand. I could get bust out some Emory cloth and make an adjustment. For $41 each very surprised they had tool creep but it is what it is.

MadCow has excellent service. Send them the pictures, they'll take care of you and would probably be grateful to know that they need to check current inventory instead of dealing with warranty claims and dissatisfied customers.

 

[rfjustin]

Just pulled out a second tube, same problem 54MM CTI 3G and 6G neither will fit. So got out the Calipers, CTI 2.125, and Aero 2.118 on both of the mounts.

How soon did you want/need to fly said retainer? I can mail you mine ASAP if that will help you avoid not being able to fly.

 

[Frederocket]

I was just prepping to install my Aero Pack quick engine mount in a 54mm rocket. I just bought a CTI reload kit and the CTI tube will not slide into the Aero Pack. 54mm should be 54mm, but are these really not compatible? I have two Aero Packs and the same problem with both. Motor fits in the motor mount just fine. Should I file/sand to get them to work? For the premium cost surprised the tolerances are off.

What is the part number on your retainer?

 

[rfjustin]

What is the part number on your retainer?

Fred, I know you were not directing the question towards me, but I think its "RA54". The one I have in hand, paperwork does not bear a part number. I can scan and post front/back on the paper insert as needed.
https://wildmanrocketry.com/products/ra54?_pos=6&_sid=4bb8de370&_ss=r

 

[crossfire]

Hi guys
I just checked my new unused RA54 retainer with a CTI 54mm case it slides in perfect.

 

[Frederocket]

Fred, I know you were not directing the question towards me, but I think its "RA54". The one I have in hand, paperwork does not bear a part number. I can scan and post front/back on the paper insert as needed.
https://wildmanrocketry.com/products/ra54?_pos=6&_sid=4bb8de370&_ss=r

Yep, that's what I have. Just pulled both of y extras from their package. Checked them with my CTI 6 grain and 4 grain cases and the fit is fine. Of course these are several years old. Thanks...

 

[bchaltraw]

I am not flying until February so I have the time, building a L2 Cert flight. I can always Chuck it up and shave some off with emery or a file. But needed a sanity check that the Aero works with the CTI. Confirmed it should, Mad Cow has already responded (thanks for the tip) talked to a member of my club they had the same problem earlier this year just sanded off a few thousands and never looked back. I wanted to share and let the manufacturer know.

 

[bchaltraw]

Did and they got right back to me! Thank you.

 

[bchaltraw]

Update of this thread so everyone knows the conclusion. The CTI cases are not uniform, I worked with MadCow and sent them my two new cases and the retainers so they could see for themselves what was going on. I also went to AMW where I got my 54MM cases and sure enough the CTI cases have a .003 difference from top to bottom. AMW was kind enough to check a few new cases and they all had the same problem. Robert even checked one of his older rockets with a 54MM retainer in it and same problem. He then went and pulled an older CTI case and everything fit just fine. So warning to new CTI 54MM buyers, the Aero Pac retainers will either have to be modified or you will not be able to get the motor into the rocket.

 

[Banzai88]

Thanks for the follow up, and great catch on the dimensional variances!

Hmmmmm.....if that additional .003 translates to inner diameter, too, I wonder how that affects tolerance stack and if it's a contributing factor to the CTI 54mm issues.

 

[Steve Shannon]

Update of this thread so everyone knows the conclusion. The CTI cases are not uniform, I worked with MadCow and sent them my two new cases and the retainers so they could see for themselves what was going on. I also went to AMW where I got my 54MM cases and sure enough the CTI cases have a .003 difference from top to bottom. AMW was kind enough to check a few new cases and they all had the same problem. Robert even checked one of his older rockets with a 54MM retainer in it and same problem. He then went and pulled an older CTI case and everything fit just fine. So warning to new CTI 54MM buyers, the Aero Pac retainers will either have to be modified or you will not be able to get the motor into the rocket.

That’s very disappointing.

 

[bchaltraw]

Thanks for the follow up, and great catch on the dimensional variances!

Hmmmmm.....if that additional .003 translates to inner diameter, too, I wonder how that affects tolerance stack and if it's a contributing factor to the CTI 54mm issues.

USN AMS E-4 84-88 NAS Miramar VF-21 Freelances (F14), CV-64 Connie! I have not checked the internal, When Madcow ships my cases back I will have to do that. Both AMW and Madcow have now reached out to CTI to let them know about the problem.

 

[bchaltraw]

Talked to Madcow and they are going to start making the 54 .003 bigger as they can only control their end of the equation.

 

[jd2cylman]

Thanks for the follow up, and great catch on the dimensional variances!

Hmmmmm.....if that additional .003 translates to inner diameter, too, I wonder how that affects tolerance stack and if it's a contributing factor to the CTI 54mm issues.

He's right, you know...

 

[Worsaer]

Wouldn’t that be considered a defect on CTI’s behalf? If we accept them, where is the incentive for the manufacturer to maintain acceptable tolerances?

 

[Worsaer]

Perhaps one more, potentially more extreme question… if Tripoli Motor Testing (TMT) determines there is indeed a material deviation in the inner diameter, might they tell CTI that all their reloads would need to be re-certified for the new case design?

 

[Steve Shannon]

Perhaps one more, potentially more extreme question… if Tripoli Motor Testing (TMT) determines there is indeed a material deviation in the inner diameter, might they tell CTI that all their reloads would need to be re-certified for the new case design?

NFPA 1125 allows for such actions to be taken by the certifying organization when changes beyond design tolerances are determined. What are those tolerances? I doubt they have been shared. Plus, CAR MCC certified the vast majority of the CTI loads. As the certifying organization, they would have to be the one to warn CTI. For TMT or NAR S&T to act in CAR MCC’s absence would only happen in extreme circumstances.

 

[David Schwantz]

But how will this affect other brands of cases??

 

[3stoogesrocketry]

But how will this affect other brands of cases??

It wont? CTI QC is garbage