CTI 54mm Threaded Forward Closure

[s201]

Hi all, this is my first post here so I hope this is in the correct location. Please move if not. I'm trying to find a threaded forward closure for a CTI 54mm motor to attach a shock cord to. I have searched high and low, but can only find them available from Wildman (https://www.wildmanrocketry.com/ProductDetail.aspx?product=3155). Unfortunately, I've have one on order for over a month now, but they are still out of stock and the estimate for getting them back in stock is another two weeks from now. And that is uncomfortably close to when I was hoping to launch this rocket. That said, does anyone know of any other shops that have them in stock? Or maybe an alternative method for attaching the shock cord to the motor? Any help or a point in the right direction is greatly appreciated!

 

[tim cubbedge]

Do you have a CTI vendor at your launch site? They usually have them or will even loan you one.

 

[s201]

Yes, there will be two vendors. One does not have the forward closure listed on their website and the other I just emailed based on your suggestion.

 

[blackjack2564]

Make one yourself with what you have.

Remove BP if any, drill out touch hole with 3/16 bit. Hand screw in a 1/4 -20 eyebolt. Fill Bp well with 5-10 min. epoxy. Done.

 

[Reinhard]

Hi all, this is my first post here so I hope this is in the correct location. Please move if not. I'm trying to find a threaded forward closure for a CTI 54mm motor to attach a shock cord to. I have searched high and low, but can only find them available from Wildman (https://www.wildmanrocketry.com/ProductDetail.aspx?product=3155). Unfortunately, I've have one on order for over a month now, but they are still out of stock and the estimate for getting them back in stock is another two weeks from now. And that is uncomfortably close to when I was hoping to launch this rocket. That said, does anyone know of any other shops that have them in stock? Or maybe an alternative method for attaching the shock cord to the motor? Any help or a point in the right direction is greatly appreciated!

CTIs threaded 54mm forward closure is not intended as a hard point for recovery systems, according to Jeroen. It's only designed for motor retention purposes. It might work, but it is not as strong as your typical aluminum forward closure.

Reinhard

 

[jkovac]

I posted a similar thread recently. The consensus seemed to be as Reinhard stated - it might work, but it's not intended as a recovery attachment point. One of the suggestions I got was to attach a Y-harness to the motor mount. Since the motor mount was already glued into the body tube when I posed the question, it was too late for me on this build. So I ended up going with AeroTech motor hardware (this is my first time using reloadable motors) but I will try the harness approach on my next minimum or near-minimum diameter rocket, because I want to fly CTI motors too.

 

[s201]

Reinhard, interesting, I haven't seen any CTI aluminum forward closures. Is it possible to buy them? In addition to blackjack2564's suggestion of making one with epoxy in the BP well, I was also thinking about epoxying a fiberglass bulkhead into one of the motor spacers and using that as an attachment point for the shock cord. I'm in the same boat as jkovac in that the motor mount is already in the rocket so it's too late for a Y-harness.

 

[blackjack2564]

Reinhard, interesting, I haven't seen any CTI aluminum forward closures. Is it possible to buy them? In addition to blackjack2564's suggestion of making one with epoxy in the BP well, I was also thinking about epoxying a fiberglass bulkhead into one of the motor spacers and using that as an attachment point for the shock cord. I'm in the same boat as jkovac in that the motor mount is already in the rocket so it's too late for a Y-harness.

1. It is for use with recovery....I have spoken at length with DR.J about this years ago...when the K-300 first came out.
He approved my method for doing this in minimum diameter 54's & 38's, when there were NO threaded closures available. I have used it many times, no issues. So have others I have shown.
I don't know where this "it's only for motor retention" is coming from???? The Aero-Pac retention system uses an entirely different threaded retention system...it screws into the BP well, not the 1/4-20 hole.
I am only refuting this, as it is mis-information, or possibly some statement previously made that was mis-construed.



2. That being said , if your project is not minimum diameter, then a Y-harness is the way to go when space is at a premium.
Also very simple to retro-fit,if you forgot or break a harness [yanking it out of a tree or cato'ing the top half of fincan...lol]

Just a few inches of coupler, & a smaller 1 inch section.
Cut slice out of smaller one ...so it fits inside the coupler.
Wedge harness between the 2 sections. Glue. Trim to fit.
Slide assembly down fincan, on top of motor mount & glue into position.....DONE. Problem Solved.



What is your project?

 

[s201]

I'm working on a 2.6" 54mm build. So not minimum diameter, but close it. The instructions stated to use the motor's forward closure for the shock cord attachment so I happily went along with the build thinking it would be just a matter of getting the right part. The problem with a Y-harness as described is that I have the screw from the rail button sitting in the middle of the fin can now and can't slide a coupler all the way down to the motor mount.

Putting an eyebolt in the forward closure and securing it with epoxy is looking like one the few viable options now.

Any thoughts on my idea to stick a fiberglass bulkhead with an eyebolt in between the lip on the top of the motor casing and the motor spacer? My thinking there is that the nosecone uses a fiberglass bulkhead with an eyebolt for the upper shock cord. It should work with the lower one, right?

 

[woferry]

I don't see how you could put anything nearly as thick as a FG bulkhead between the top of the spacer and the top of the case, there isn't supposed to be any slack there, if there was I don't see how the motor would stay together (i.e. the forward or aft closures would be able to separate from the liner, at least enough that the liner O-rings would no longer seal). And I certainly wouldn't try to trim a spacer to create that extra space. Now if you're always going to fly with a spacer (which you'd have to with your proposal, since the forward closure extends past the end of the case opening while the spacer doesn't) I would think you could probably set some sort of retention solution inside the spacer, basically using the spacer in a fashion similar to what Jim suggested with the coupler (or epoxying-in a threaded rod, nut, eyebolt, etc). It wouldn't seem any different to me than doing the same with the forward closure itself, perhaps even slightly better since the spacer at least has a lip at the top to keep your epoxy job from pulling out, while the forward closure's charge well is pretty smooth so you have to add holes or the like (really roughing it up at least) to give the epoxy something to grab onto I'd think. And at least you'd always get a fresh closure with the smoke grain (just make sure to remove the BP if you'd be sealing-off the hole through to the top of the casing) rather than having to re-use one or epoxying in a new bolt to a fresh closure every time, down-side is you'd always have to fly a case at least one size larger than your motor (and any 6G motors would be extra complication of needing a modified XL spacer as well as a modified standard spacer). So to clarify, this thought (no claim as to whether it would work or not) would not modify the exterior of the spacer at all (wouldn't want to affect how it fits in the casing), only attach something to the empty volume inside it, for recovery attachment. I'd also note that you obviously can't fill the entire spacer volume (probably wouldn't want to anyhow with all the added weight), since a lower spacer or the motor's forward closure extends into the lower volume of the spacer at least a bit. So you would need to create some sort of false bottom part-way up the inside at least long enough to get the epoxy set (where the charge well approach at least gives you a cavity that is only open on the top to begin with).

 

[s201]

Thanks for the detailed reply woferry!

In regards to the spacers, I was considering two possibilities:

1. Putting a fiberglass bulkhead between the top lip of the motor casing and the spacer. You're right, there is currently no room between them. However, an FG bulkhead is ~2.5mm thick so I was thinking that it might be possible to stick it in there anyway and have the motor extend past the end of the case by that amount. The O-ring would still be enclosed in the casing, but then the motor retainer would have to account for the added length since I'm assuming that having any amount of play between the aft closure and the retainer would be... not great. Overall, messing with the placement of the motor in the casing is screaming "bad idea" to me.

2. Putting the bulkhead inside the top spacer. Right now, I have a three grain case, but am only using one grain motors. For the foreseeable future, I'll be using at most 2-grains so I'll have at least one spacer. Beyond that I start to run into stability problems. And also the motor mount is as long as the 3-grain case. I don't know if it's recommended to use a case that's longer than the mount or not. I'm guessing probably not. Anyway, long story short: I'm okay with the limitation of requiring at least one spacer for now at least. I didn't consider the challenge of epoxying it in place inside the spacer though. That's something I'll have to think about.

 

[gerbs4me]

Make one yourself with what you have.

Remove BP if any, drill out touch hole with 3/16 bit. Hand screw in a 1/4 -20 eyebolt. Fill Bp well with 5-10 min. epoxy. Done.

Clever idea!

 

[woferry]

Just to zero-in on this comment:

And also the motor mount is as long as the 3-grain case. I don't know if it's recommended to use a case that's longer than the mount or not. I'm guessing probably not.

Absolutely no issues with a shorter mount than the case. The mount just has to be long enough to hold the motor straight, I'm not aware of any official rule but it seems to me so long as the mount is ~2-3x the motor diameter it's probably fine for any case length. Motor mount adapters (like those that let you fly a 38mm motor in a 54mm MMT) are often very short compared to the motors you would put in them. But if there are Cg and stability concerns with a heavier motor those would definitely still apply.

 

[STORM]

Jeroen suggested putting one of Giant Leap's Hardpoint anchors in the top of a spacer. Here is a link to the thread: https://www.rocketryforum.com/showthread.php?5729-Cesaroni-Grain-Spacers-Game-Changers

Zach

 

[Banzai88]

1. It is for use with recovery....I have spoken at length with DR.J about this years ago...when the K-300 first came out.
He approved my method for doing this in minimum diameter 54's & 38's, when there were NO threaded closures available. I have used it many times, no issues. So have others I have shown.
I don't know where this "it's only for motor retention" is coming from???? The Aero-Pac retention system uses an entirely different threaded retention system...it screws into the BP well, not the 1/4-20 hole.
I am only refuting this, as it is mis-information, or possibly some statement previously made that was mis-construed.

View attachment 290122 View attachment 290123

So you're saying that this:

, with an eyebolt stuck in it is approved by Cesaroni to hold the recovery harness? Not disputing what Dr. J said at the time, but Aero Pack's web page specifically says "Adapters are for retaining motors to Aero Pack bulkhead retainers only and not to be used for attaching recovery hardware.", so there's a definite disconnect there somewhere.

I would not dispute, though, that your method of drilling a hole and epoxy filling the charge well is plenty secure, as I've seen evidence of other folks doing it without issue.

Jeroen suggested putting one of Giant Leap's Hardpoint anchors in the top of a spacer. Here is a link to the thread: https://www.rocketryforum.com/showthread.php?5729-Cesaroni-Grain-Spacers-Game-Changers

Zach

For review:

And the link to the anchor point: https://giantleaprocketry.com/products/components_recovery.aspx#Shockcord_Hardpoint

I wonder how one is supposed to keep the adapter up in the spacer and not have it rattling around? I'm guessing that sacrificing one to JB weld the thing in place would be a noble pursuit.

Either way, it looks like this product will solve the OP's issue quite nicely (glued in to the airframe or case mounted, as shown above), although the ring/y harness that Blackjack illustrated would be lighter. If I were using this mount for a MD rocket, I would be sure to use a double kevlar loop instead of a knot on the eye, though.

 

[s201]

And the link to the anchor point: https://giantleaprocketry.com/products/components_recovery.aspx#Shockcord_HardpointI wonder how one is supposed to keep the adapter up in the spacer and not have it rattling around? I'm guessing that sacrificing one to JB weld the thing in place would be a noble pursuit.Either way, it looks like this product will solve the OP's issue quite nicely (glued in to the airframe or case mounted, as shown above), although the ring/y harness that Blackjack illustrated would be lighter. If I were using this mount for a MD rocket, I would be sure to use a double kevlar loop instead of a knot on the eye, though.

Wow, that looks great! One thing I'm confused about though, in the thread linked to it states: "First the outer ring was removed. The remaining spokes were then press-fit into the Pro38 case spacer." How is the outer ring removed? It's all one piece of aluminum, right?

 

[dhbarr]

Wow, that looks great! One thing I'm confused about though, in the thread linked to it states: "First the outer ring was removed. The remaining spokes were then press-fit into the Pro38 case spacer." How is the outer ring removed? It's all one piece of aluminum, right?

See how shiny those new edges and corners are?

 

[blackjack2564]

So you're saying that this:

, with an eyebolt stuck in it is approved by Cesaroni to hold the recovery harness? Not disputing what Dr. J said at the time, but Aero Pack's web page specifically says "Adapters are for retaining motors to Aero Pack bulkhead retainers only and not to be used for attaching recovery hardware.", so there's a definite disconnect there somewhere.

I would not dispute, though, that your method of drilling a hole and epoxy filling the charge well is plenty secure, as I've seen evidence of other folks doing it without issue.





We are saying the same thing. The Aero-pac is Not for recovery. You do NOT put an eye-bolt in the top of red threaded gadget going into BP well.

You can however attach E-bolt to the part that glues into airframe, from which the "extenders" go into that red gadget to hold motor in place.

By the way...I am NOT drilling a hole. Just barely enlarging the existing touch hole with a 3/16's bit. The hole is tapered, you have to true it up to get a E-bolt in.

With a Spacer I just turned a BP diameter down to fit inside and put E-bolt on BP.

 

[s201]

See how shiny those new edges and corners are?

Yeah, I figured there were some modifications involved. I'm fairly new to all of this, how would I go about removing the outer ring? I don't have much experience working with metal.

 

[dhbarr]

Yeah, I figured there were some modifications involved. I'm fairly new to all of this, how would I go about removing the outer ring? I don't have much experience working with metal.

Best choice: find a friend who already has the tooling and experience to do it. Small high-RPM cutoff wheel for rough shape w/ hand smoothing could do it, or heck; even a hacksaw and some files if you have the patience.

If you're going to attempt this yourself, best to practice on some scrap first maybe?

 

[s201]

Quick update on this: I went with Banzai88's suggestion to use the Giant Leap motor mount hardpoint. Attached is an image of the progress very similar to the image posted above. For reference, I was able to do the required modifications myself with hand tools only. The outer ring is thin enough to cut with tin snips and then I filed down the spokes until they were able to fit inside the spacer. Finally, I sanded the inside of the spacer and secured the hardpoint in the spacer with epoxy. The only downside is that I'll have to figure something else out if I ever want to fly a 6-grain motor in this rocket, but seeing as I'm only using 1-grain's right now, I'll cross that bridge when I get to it.

 

[Banzai88]

Quick update on this: I went with Banzai88's suggestion to use the Giant Leap motor mount hardpoint. Attached is an image of the progress very similar to the image posted above. For reference, I was able to do the required modifications myself with hand tools only. The outer ring is thin enough to cut with tin snips and then I filed down the spokes until they were able to fit inside the spacer. Finally, I sanded the inside of the spacer and secured the hardpoint in the spacer with epoxy. The only downside is that I'll have to figure something else out if I ever want to fly a 6-grain motor in this rocket, but seeing as I'm only using 1-grain's right now, I'll cross that bridge when I get to it.

Looks good! Thanks for the report on the items, might have to try this out myself.