Crooked fin on Wildman Mach 3

[Jmhepworth]

I tried two new skills building a Wildman Mach 3. I haven’t built a minimum diameter rocket (other than paper and balsa) so this was new to me. I used fin alignment guides for the first time , and I used ProLine 4500 epoxy for the first time. I didn’t do any research to understand the characteristics of the epoxy, expecting it to behave like Rocketpoxy or Aeropoxy. It set up suddenly, far faster than I was expecting And I really didn’t know how to use the fin alignment guides. I was more worried about epoxying the guides to the airframe than making sure the fins were straight and ended up with one rather crooked fin. The tip of the leading edge is about a quarter inch left of what it should be. I still don’t know how I did that using an alignment guide.

So here’s my dilemma. Should I try to remove the crooked fin with a heat gun, just get a new body tube and fin set, or fly it as is and let aerodynamic forces take the fin off for me? I doubt that I would let it fly if I were doing the flight safety review, so the last choice probably isn’t a good one (although it might be a spectacular shred). I’m inclined to start over and chalk it up to yet more lessons learned the hard way.

Thoughts?

Joe

 

[Jmhepworth]

Never mind. I pushed on the fin from the side and it popped right off. A little sanding, some acetone, more epoxy and it’s on straight. Don’t know what I was worried about.

Joe

 

[blackjack2564]

How to do it: I built M-2 and M-3 here's for 2 fins go on same.
https://www.rocketryforum.com/threads/cj-builds-wm-mach-2-rocket-2-stage.144264/

Post 7

 

[Jmhepworth]

Thanks, CJ. I should have gone looking before trying something new. I have a Mach 2 as well (and a Mini Mach 2) so I think I’ll read through that thread before building it.

 

[David Schwantz]

Myself, I would be more worried that it "popped right off". What did you do for surface prep? Wash with warm soapy water, clean with alcohol,sand with at least 60 grit, I like 36 grit, I also like to "X" the fins and tube were glue goes with a permagrit tool in the dremel. Also drill a series of holes along the fin root 1/8" up or so to act as epoxy fingers.

 

[Jmhepworth]

Wash with warm soapy water, 60 grit sandpaper, acetone, epoxy. No fillets yet, so epoxy fingers wouldn’t have done anything. These are not thick fins. There isn’t a lot of surface bonding without fillets.

 

[David Schwantz]

I am just finishing my Mach 2 now.

 

[Jmhepworth]

Those are nice fillets. You won’t ever see pictures of mine.

 

[David Schwantz]

thank you.

 

[REK]

You mentioned the epoxy settled in faster than you thought, exactly how fast? It sounds to me that you used more hardener than necessary. I believe proline 4500 has a different mix ratio than a 1:1.

 

[Steve Shannon]

You mentioned the epoxy settled in faster than you thought, exactly how fast? It sounds to me that you used more hardener than necessary. I believe proline 4500 has a different mix ratio than a 1:1.

Sorry for the correction, but adding more hardener to epoxy will not cause epoxy to harden faster. Hardener is part of a stoichiometric mixture (+/- some percent), not a catalyst. Adding excess hardener will simply result in an epoxy that has the excess hardener trapped within it, usually resulting in a soft or rubbery mixture.

 

[rharshberger]

Sorry for the correction, but adding more hardener to epoxy will not cause epoxy to harden faster. Hardener is part of a stoichiometric mixture (+/- some percent), not a catalyst. Adding excess hardener will simply result in an epoxy that has the excess hardener trapped within it, usually resulting in a soft or rubbery mixture.

An exception to that is that MEK-P catalyzed polyester resin are dependent on ratio, the more MEK-P the faster the cure at 1.5% its pretty normal (quick by our standards) at 3% mix and pour immediately or its game over. We had times in my Dads fiberglass and cultured marble shop where quick setup was desired (like 15 mins to de-mold).

 

[REK]

Sorry for the correction, but adding more hardener to epoxy will not cause epoxy to harden faster. Hardener is part of a stoichiometric mixture (+/- some percent), not a catalyst. Adding excess hardener will simply result in an epoxy that has the excess hardener trapped within it, usually resulting in a soft or rubbery mixture.

Whoops thats my bad, yes you are right. I confused it with the exothermic reaction that is generated by the hardener. If I am not mistaken, proline does not heat up as much.

It is still strange to me that his resin cured faster than average.

 

[Jmhepworth]

And I had a pretty serious exothermic reaction. Mostly because I mixed too much at once.

 

[REK]

And I had a pretty serious exothermic reaction. Mostly because I mixed too much at once.

Did you have it in a cup? This is where I have had problems, is a lot of resin in a confined space. It will build up a lot of heat.

 

[Steve Shannon]

And I had a pretty serious exothermic reaction. Mostly because I mixed too much at once.

Mixing well in a hot drink cup (unwaxed paper, not foam) cup and pouring into a shallow dish, like a used microwave entree dish, will help keep it from kicking.
Leaving it in a deep cup frequently makes it kick.

 

[Jmhepworth]

I used a cup. Lots of heat. Lesson learned. I’ve since finished the Mach 3 fillets and built a Mach 2, including the fillets. I love the Proline epoxy. I just needed to get used to it.

 

[David Schwantz]

I like to use the Dixie bathroom cups. Perfect size, and Like Steve said, no wax. Also use them for mixing paint, never reuse them as they are cheap.