Motor Mount Fin Slots for TTW

I recently made an “indestructible” rocket for my 3-year-old that had 3/32” papered (tissue) fins mounted through-the-wall of a BT-20 tube. Of course, on the way to it’s first launch, something heavy fell on it and snapped the glue joint on a fin. I’m amazed the fin itself didn’t break, but it gave me an idea...

TTW fins could be even stronger if they fit into slots in the motor mount. (I know Estes already does this with their plastic engine mounts, but my balsa version is much lighter.)

Photos are of my current build using this technique, a BT-55 tube with fin slots in a 24mm motor mount.

Very nice! I know some folks do this not for strength, but to control where their epoxy goes / how much goes in.

My construction is all balsa & wood glue, but thanks for the tip on epoxy control!

The completed rocket is ready to fly tomorrow!

I use fin slots on more than a few of my MPR and HPR builds these days, originally they were suggested as a method for fin attachment by my L3CC. Every time I have used them they have worked great.

Thanks for the tip on L3CC. I've got some reading to do!

Aside from adding extra mounting stability for the fin, I like my slots because they add another connection between the body/motor and weigh almost nothing. In fact, my completed rocket weighs only 52 grams w/o engine.