Reliable/Strong Adapters

[llickteig1]

While mulling over new project ideas, a recurring theme for me is to be able to accommodate some physically long 38mm EX motors (18"-24") while still being able to fly 54mm in the same rockets.

The length itself doesn't concern me too much, but typically these long EX motors are pretty hard-hitting and high average thrust (~J750) and some concern about ripping the snot out of a 38mm/54mm adapter has come to mind. I just need a solid and reliable way to transfer the energy from the 38mm adapter to the 54mm motor mount.

Anyone have anything to offer regarding well-constructed adapters, either commercially available or roll your own? Is using an adapter with this much thrust is a bad idea?

Thanks, --Lance.

 

[LMazza]

I've been thinking about this very same thing. Other than the Dr. Rocket adapter closures I don't know what would take long, high thrust 38mm motors.

 

[Austin]

I would make an adapter. Since you are using EX motors, the 54mm to 38mm Dr Rocket end closures are not an option, unless you actually use threaded EX casings, which is doubtful.

I recommend you make an adapter similar to the one I use for my 98mm to 75mm motors, only on a smaller scale. You only need foot or two of G12 38mm tubing for a Motor Mount, a couple 54mm to 38mm Centering Rings, preferably home made from 1/2" thick ply, an AeroPack 38mm Retainer and a 1/8" thick piece of aluminum plate to make your own oversized bottom Centering Ring.

Glue the Aeropack on one end of the tube with JB Weld just like the instructions state. Drop the aluminum CR you made down over the tube until it sits flush against the Aeropack, then slide a Ply CR over to hold the aluminum plate against the retainer. Epoxy the Ply CR in place , then epoxy another ply CR at the end of the adapter and you are done with building.

I make the Aluminum CR bottom plate at the smallest diameter of your rocket. If you are using the adapter on a 3" rocket or larger, make the aluminum plate 3" in diameter. The entire plate will sit at the bottom of the rocket. Thrust will be transfered to the retainer and plate and you will NEVER shoot a motor up through your rocket...not unless the motor is so powerful that is can push an aluminum and steel Aeropack Retainer, then through 1/8" thick aluminum, the 1/2" ply CR and finally a foot or two of G12 MMT Tube...it's just not going to happen!

To mount the adapter, build your rocket with three or four T-Nuts in the bottom ply CR. If it is already built, you can use the brass threaded inserts like PML uses with their adapter. Three or four stainless bolts hold the plate on and you can move it from rocket to rocket. For smaller models, I would use 6-32 or 8-32 bolts and for larger models like L3, I usually use 1/4-20 bolts to install the adapter.

Listed below are some pics of my 98mm to 75mm version, but the smaller ones work the same. If you are doing EX, then finding someone to cut out an aluminum plate for you should be no problem. Our Prefect for our TRA club actually made his from Stainless. Note my adapter plate was bolted to the ply inner CR, but you can glue yours since it is smaller. Also, one of the best benefits is you will never scorch the bottom of your rocket again as the metal plate takes the heat.

Pics:
https://www.rocketryforum.com/ctulanko/album/index.php?dir=423inch

https://www.rocketryforum.com/ctulanko/album/index.php?display=blu/blub21.jpg

https://www.rocketryforum.com/ctulanko/album/index.php?display=harm/hb56.jpg

Carl

 

[lalligood]

Speaking of Aero Pack retainers, they do make popular sizes of motor adapters that are CNC'ed aluminum, just like their retainers. You *have* to use them in conjunction with their retainers. An expensive solution, but one that should be able to handle whatever abuse you put them through too!

HTH,