Fin Strengthening Options

[Bret PackardParticipant]

My PML Tomahwk is one of my favorite rockets. It just flys great. Unfortunately, it also seems to rip a fin every freaking flight no matter how it lands. It’s on a 48″ chute and comes down pretty slowly, but the fins are so large that they just grab the dirt and tear from the bottom of the airframe joint.

So I’m going to build a new one from a phenolic based kit and fiberglass it completely. My question is this: will I gain more strenth by running some 4-6oz cloth tip to tip over the stock .062 G-10 fins or should I get the .093 G-10 fins with no T2T. I haven’t killed any of my glassed birds so I really don’t know how much strength I am gaining from the reinforcment I’ve been doing. Any ideas/comments/suggestions are appreciated. Thanks.

[Warren B. MusselmanModerator]

tip to tip is always the way to go BUT you can’t do it on a quantum tube airframe – only on phenolic or composite.

Warren

[Ed Dawson]

And really rough up those G10 fins (as well as the BT) to get good adhesion!

[Doug GerrardParticipant]

My preference would be to go with the thicker fins. However, the strength REALLY does depend on many different factors including, like Warren pointed out, the tubing you are using and more directly, how well of a glue joint you get.

One thing for you to consider is fin flutter. I have seen 1/16th inch G10 fins break off of a rocket due to fine flutter on an I motor. Of course the shape of the fins largely contributes to fin flutter and the thicker fns would add more weight but I just thought I would mention it.

Doug

[Art HoagParticipant]

Go with the thicker fins. I always regretted building that Endeavor with those thin fins.

Art

[Bret PackardParticipant]

Thanks for the advice guys. To respond to a few comments, I don’t think I’ll build any more Q-tube kits, glassing is so easy and gives such a nice finish plus the added durability it just makes sense to go with phenolic. I hit the G-10 fins hard with 60-80 grit for a good bonding surface, I agree with Ed here, scuffing that up well can make or break the rocket (literally :P).

I think I’m goping to go with the thicker fins because the more I look at the PML kits I have those fins are just so dang thin. This particular project I am far more concerned about it lasting than being a contender for some altitude contest. So I’ll be going with the .093 G-10 fins, and I still plan to do a light layer of T2T. Hopefully that will give me everything I need.

[elviss_boy]

Where are they breaking? Is it at the point where the fin meets the tube or a tip of a fin?

[Bret PackardParticipant]

They tear about 1/4 to 1/2″ where the bottom of the fin joins the body tube.

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