High power aft ejection

[tollyman]

I've been thinking about the idea of doing a rear eject recovery system on a scratch build. The way I would do it is different than what most people would do. The build would probably be 3" fiberglass and maybe stand 5ft tall. The fin can section would be entirely constructed in a 3" coupler section with a 38mm motor mount so essentially it would be through the wall to the coupler section. There would be fin slots cut all the way to the back so that the entire coupler/fin can can slide out. Shear pins would be used to hold it in place during boost/coast. I've been thinking of a few different ways to transmit the trust to the body tube, and either a traditional Estes style thrust ring on the inside or a thrust ring on the coupler fin can were a min diameter motor. This could be either single or dual deployment. Dual deployment could be accomplished with a cable cutter releasing the main chute, a tender descender used in the same manner, or deploy a chute with a chute release with drogue (or as drogue). What are your thoughts? See any flaws I'm missing? Looking forward to your input

 

[rharshberger]

If using a thrust ring I would recommend an internal one, due to thrust the external (on rear of fincan) might push into the airframe due to the fin slots (think petals of a flower look).

 

[tollyman]

If using a thrust ring I would recommend an internal one, due to thrust the external (on rear of fincan) might push into the airframe due to the fin slots (think petals of a flower look).

Yeah good call, my first thought was that an internal thrust ring might snag a parachute, but it really shouldn't be too big of an issue

 

[Rocketjunkie]

Glue a short section of coupler ahead of the fin can coupler to act as a thrust ring. Make sure you sand the crap out of the inside of the body tube and short coupler outside. Also, once you fillet the fins, it will lock the fin can in place. Note that you will only be able to tack the fins to the coupler and NONE of the glue can seep out the sides onto the coupler unless you install the fin can while the glue is still wet.

 

[tollyman]

Glue a short section of coupler ahead of the fin can coupler to act as a thrust ring. Make sure you sand the crap out of the inside of the body tube and short coupler outside. Also, once you fillet the fins, it will lock the fin can in place. Note that you will only be able to tack the fins to the coupler and NONE of the glue can seep out the sides onto the coupler unless you install the fin can while the glue is still wet.

Do you think also drilling and tapping some holes where the thrust ring woul be epoxied (assuming fiberglass) and then using small machine screws would be a good choice as well?