Centering ring positioning

[Nostalgia4Infinity]

Hello all,
I’m building a Mac Performance Black Fly and I had a question about the motor mount and centering rings.
The instructions call for setting the front CR so that there is about 1/8” of the motor tube sticking out of the front, presumably enough for an epoxy fillet.
My question is, would it be better to set the front CR so that it’s touching the front of the fins, so that the fins are sandwiched by the front and rear centering rings? Are there any downsides to going about it this way? I feel like if anything, it might add rigidity to the whole fin/motor mount assembly…


Vs


Any input welcome !

 

[Titan II]

Six of one, half dozen of the other.

Don't forget to consider the rail button location.

 

[jmasterj]

I would touch the fins to make internal fillets easier, but I think it's personal preference. Think about the length of the kevlar leader with that difference: where will it fall on the airframe and how are you setting up your recovery package?

 

[bjphoenix]

I prefer putting the centering ring a little farther down the motor tube so I can more easily get a good fillet on it. For fins that extend to the motor tube I prefer to build the fin can complete outside of the rocket then slide it in from the back. This requires extending the slots to the rear of the airframe. If the design doesn't work with then then I'll glue the front ring to the motor tube positioned so it will be at the front of the slots. I attach something to the rear ring so I can pull it back out then slide it on the motor tube, put the motor tube in the rocket, and glue the front centering ring. The rear ring is not glued yet. Put the fins on, glued to the motor tube and put little fillets on the outside of the airframe. Now take out the rear ring and put real fillets inside from the back end. After all that, glue the rear ring in.

 

[David Schwantz]

Yes, sandwich the fins as the lower picture shows. Now you are transferring thrust through MMT, lower CR, the fins, the upper CR and the body tube