Tailcone/Boattail for a 3.1" BT and 29mm MMT

[tawridgeway]

I received a kit as a gift that I'm planning to modify. I'm looking to drop an E bay in the middle for dual deploy and shove some tracking in the nose cone, but my current task is looking at the motor retention.

I love the Aero Pack system and am using it on almost all of my recent builds. I noticed that they have tailcone retainers that look super slick. Unfortunately, it seems that the dimensions are (understandably) limited in options. As the title mentions, I'm looking for a tailcone retainer that accommodates a 3.1 inch body tube to a 29 mm motor mount tube. Does anyone have a lead on a similar product that might do the job?

My other idea is to get a standard 29 mm Aero Pack retainer and then 3D print a shell to bond to the retainer and accomplish a similar end result. Somewhat worried about the thermals of the exhaust with the plastic, but it might work; anyone tried this before for custom sizes/profiles?

 

[SolarYellow]

Cut a nose cone to build a boat tail that meets the retainer OD.

 

[Hobie1dog]

Cut a nose cone to build a boat tail that meets the retainer OD.

+1

 

[Neutronium95]

Giant Leap Rocketry has a few products that migh work.

The Slimline tailcone retainers are pretty slick, but there isn't one in the size you want. You could upsize the motor mount to 38mm and have a compatible option.

If you decide to cut down a nosecone and embed a retainer into it, the normal Slimline would be perfect, since it has a smaller outside diameter than the Aeropack, and the outside surface can be glued to the nosecone, since it uses an internal snap ring.

 

[Budro0]

I received a kit as a gift that I'm planning to modify. I'm looking to drop an E bay in the middle for dual deploy and shove some tracking in the nose cone, but my current task is looking at the motor retention.

I love the Aero Pack system and am using it on almost all of my recent builds. I noticed that they have tailcone retainers that look super slick. Unfortunately, it seems that the dimensions are (understandably) limited in options. As the title mentions, I'm looking for a tailcone retainer that accommodates a 3.1 inch body tube to a 29 mm motor mount tube. Does anyone have a lead on a similar product that might do the job?

My other idea is to get a standard 29 mm Aero Pack retainer and then 3D print a shell to bond to the retainer and accomplish a similar end result. Somewhat worried about the thermals of the exhaust with the plastic, but it might work; anyone tried this before for custom sizes/profiles?

Erockets has some printed tailcones which I have used before: https://www.erockets.biz/semroc-tail-cone-bth-70-1-75-29mm-motor-sem-tc-70ha-petg/

I normally use a retainer on the end of it and bond the tailcone to the MMT - I have not noticed any issues with melting or warping. It can definitely be done.

 

[tawridgeway]

I appreciate the feedback y'all, I think I'll try to modify a nose cone and bond it to a retainer. If it's successful I'll try to follow up with some pictures.

 

[tawridgeway]

Alright, I finally finished this project and figured I'd update this thread in case anyone wants to do something similar.

I started this all off in CAD. I'm lucky enough to have access to Solidworks, so that was my poison of choice here. The geometry wasn't based on a whole lot other than wanting: steady curve transition from BT to retainer, thick tailcone that can handle a hard landing, and plenty of surface to bond the retainer to. The OD at the top is the same as the OD of the BT (standard LOC Precision tube), and the length of the tailcone was, "eh, that looks pretty good."
The goal was to print this geometry and then JB Weld the outer part of an Aeropack retainer to the 3D print. The lower shoulder was sized to have a little slop around that Aeropack ring to glob up enough JB Weld. Everything else is based on a minimum 1/8 in thickness.

The picture below shows the print after post-processing. Looking back, 1/8 in was way overkill, especially because I had this printed in PETG. The goal with PETG was just a slightly higher strength and good heat resistance for the hot summer launches (Southern California type deal). Finishing was done with interior/exterior wood filler, diluted with water. Let that fully set and hit with some super fine grit sandpaper until smoother than your best pick up line (this is a super similar procedure to how I do seam filling).

Here I'm setting up and doing the epoxy bond. When calculating the spacing of all my parts, I purposely put the retainer around 1/16 in too far from the bottom of the BT. This meant that when I went to attach the tailcone, I could just push it back until it made a (near) perfect mate (you need to also put the thrust ring/aft closure in the retainer, that changes how much it tightens down). The tape in the first picture is to keep goop squarely out of the threads. After slipping the tailcone on, I did a bit of fussing to align it near perfectly before leaving the room and letting the rocket gods guide the cure.

Once fully cured, I pulled the tailcone off and cut the tape out with an exacto knife. While some tape is impossible to get out and blocks some of the JB Weld bond, I'm confident that there is still plenty of surface area.

Here is the final product integrated with the rest of the rocket. This is a Sky Fieri kit from LOC Precision, modified for dual deploy and with this tailcone. The grey is just primer to give it a little protection before the first flight.