Minie Magg goes thud. Fin repair help needed.

I had a dual deploy failure on my Minie Magg. The main charge did not fire (I think a loose battery to altimeter connection was the culprit), and the rocket landed hard on gravel, snapping off a fin at the root. The fins are modified to be TTW all the way to the MMT. So, as the picture shows, the fin slot is still filled solid with the plywood fin tang. How can I clear out the fin slot and install a new fin?

If it matters, the rocket was built by a friend who used minimal glue fillets but glassed the whole thing.

I have hand tools, dremel, saber saw, sawz-all, circular saw, and a table saw. Maybe I can make a plunge cut with the circular saw to clear out most of the material? Any help is greatly appreciated. Thanks!

Ouch. That is going to be a difficult fix.


The plunge cut sounds like it could work. My main concern would be large broken pieces of wood and epoxy inside of the tube that won't fit out the slot. They will rattle around unless you find a way to get them out.

You could also slit on either side of the fin, clean out the old fin, epoxy the new fin in the middle of the now wider fin slot, then fill in with thickened epoxy and refillet.

Best of luck on the repair!

The Mini-Magg is big enough, you should be able to drill a large hole >1" in the aft CR to help get the old fin out and glue a new one back in. Plug the hole afterwards, or leave it for next time.

Had the same thing happen, my simple fix:

Since fins are originally mounted with LOC's small fin tab being slotted & you push a wedge of wood through, it doesn't go all the way to MMtube.

Use your saw and plunge cut through the tab if it's still there.
Cut a new fin with full tab long enough to reach MMtube.

Install as regular fin to MM. Glue root to MM and fillet external.

After my first MM launch, I had to get inside to add a little epoxy, so I did this:


On the second launch I hit some rocks and a fin busted into half. I think I'm going to just fiberglass them.



On yours, I'd consider sanding it flush and doing tip to tip. The other thing I'd consider doing would be sawing a small bit of the rear CR out at the fin to MMT joint, and hammering a long thin screwdriver down to knock out what's left of that fin tab.

Good ideas, guys. Thanks. The broken fin tab does go all the way to the MMT, so I have lots of wood to remove.

Seems like a good thread to share similar experience. I did just what Jim said, get the old bits out and re built new fin with full length tab (typical TTW style) I had a few left over "bits" of wood that were rattling around inside the fin can. I just made a heavy layer of epoxy when attaching the new fin. Give the rocket a nice "shake" until all the loose pieces come into contact with the epoxy on the inside. Good luck and take your time.

If you have access to a router you can cut the old piece out. I have done this a few times and it works great.

Hey Buckeye, sitting in Hitckcock Hall as I read this lol, I'm a Buckeye too. I would suggest T2T glass in the fins when this is fixed, will greatly reduce fin breakage. A layer of 15 oz FG will do wonders. In regards to battery terminals coming loose, what altimeter are you using? Does it have the battery directly on it, or does it have an external power source? Either way you can probably rig it so that a zip tie or two will prevent this from happening again.

Hi there, Whodunit. I know Hitchcock Hall very well and also spent many hours in the old Robinson Lab (probably before your time. Now known as Scott Lab.)

The fins were glassed. All bets are off if the chute doesn't deploy! I gotta get the old fin out before I can do anything further.

Battery is wired as shown here:

https://www.rocketryforum.com/showt...ie-Magg-with-Cable-Cutter&p=447546#post447546

I am really surprised that I may have lost power as this setup seemed very secure. The ematch did not fire. However, post-flight, I turned on the altimeter and got a low voltage warning and I was able to jiggle the battery clip ever so slightly. Next time, I will wrap the whole damn battery and clip with electrical tape! I also suspected a short in the e-match due to the Cable Cutter, but I was able to successfully fire the ematch and another during ground testing