Detatchable Fin Techniques for a "Marvin Martian Jr." HPR?

[jmmome]

One of the first things I realized when planning this 5 1/2 feet tall rocket is that I won't be able to get it out of my basement because of the width of the three fins. I may be able to permanently attach two of the three, but certainly not the third and still get it through the basement door.

Since the fins will be of 1/4" aircraft plywood, the first thing I thought of was to create a "sandwich" of 1/4" plywood around either side of the fin (simply a fin analog with a 12" root at this point, of the same 1/4" material) which will extend maybe 5" past the football-shaped body, with a 1/4" x 1/4" spacer at the bottom to hold the opening at the bottom.

Epoxy and fiberglass this outside sandwich to the 4" dia. internal body tube, and when cured, drill four holes through the sandwich and the 12" fin root through which I'll attach fender washers, and wingnuts or nuts/bolts. Should be able to remove and re-attach the fins.

What other methods have you used? What are the things to watch out for when creating detachable fins?

My thanks to Dan Welling of the St. Louis "Kaboom Krewe" for spending time with me last night on the phone to discuss their amazing LDRS 38 project.

 

[BDB]

No responses?!

I’m considering doing the same thing on a large sonotube build. Did you ever try the “fin sandwich?”

 

[0011001100]

I've never personally done this, however, I have helped out with prepping flights that have the fin bolted on how you described. It works well on the L3 motors so I see no reason for it not to work for you here if done properly.

 

[BABAR]

Just floating the idea, not that I have tried it.

Base of the fin is like an inverted T. The side pieces can be 1/4”, or metal plate

You have three slotted tracks on the outside of the body tube, all except the actual fin slot are hidden by your foam.

Slots are open at the base of the rocket just above the bell. Top of the slot is closed off with stops.

At the launch or display site:

Take bell off.

Slide the fins from the bottom until they hit the stops.

If putting the bell assembly back on doesn’t provide enough hold to keep fins from sliding back out (I am imagining the bell attached to a metal or plywood “plate” with a hole in it for the motor mount, bolts to hold the bell/plate onto the rocket), you may ne some other bolt/washer or other device to keep each individual fin from sliding out of its slot.