Odd Shaped Fins

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mccoy300

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My wife wanted to build a rocket with a star theme. I simmed this design in Rocksim, and it shows to be stable, but there was a note that said fins with cutouts may not sim correctly. Anyone with experience know what to expect?
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You just won this thread.

Anyway, it looks stable from here. Those fins are not that crazy, surprised Rocksim is even complaining.

Neat looking rocket. I hope those aft points are reinforced for landing somehow. :)


That was the dad joke of the century. you just wont the internet... Fins are 1/8th ply, i should think it is sturdy enough. going to put this one up on the apogee medalist motors and see what happens.
 
Fins are 1/8th ply, i should think it is sturdy enough. going to put this one up on the apogee medalist motors and see what happens.

FYI - over time, I broke all pointy-ended 1/8th ply fins I ever glued to my rockets.
A few during landings, most during transportation.

YMMV,
a

P.S.: If it has a pointy end, it better be made of, or reinforced with, fiberglass.
 
Appreciate the input. As they break I suppose best coa would be to sand to bare wood, fiberglass then refinish?
 
The fins on my Starlight upscale are 1/4 balsa. To reinforce the points, I replaced the bottom 4" of leading edge with 1/4" dowel. Then I laminated 1/16" onto the trailing edges of the fins (which were left square). Those bad boys cut into the dirt like a machete, but they haven't broken.

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Very cool design! But I'd be surprised if you didn't break a tip here and there.
 
I think that looks amazing... Those fins will do fine. Pointy fins are awesome... FB_IMG_1518130987236.jpg

Sent from my VS988 using Tapatalk
 
The popularity of this thread is going to be meteoric.
Which direction do meteors generally travel? (Hint: not up. ;))

As for the rocket, pointy fins have been done before. As an example, the Fliskits Adfecta. So there's nothing inherently wrong with the design. Using plywood for the fins is a good idea - a wood with a single grain direction, such as balsa, would make the side points very weak. Maybe use a parachute one size up from what you'd normally use for a rocket that size and weight.

There's usually a rule about not trying to catch a rocket while it's on the way down. Definitely follow that rule with this one!
 
I did go with a 24 inch chute just in case. And yea I only really ever try to catch a rocket if it is headed for the drink. I think we have all had that moment. Rocket recovery via pool skimmer sucks.
 
Appreciate the input. As they break I suppose best coa would be to sand to bare wood, fiberglass then refinish?

The only successful path to repairing broken ply fins is fiber-glassing over them.

I did try sanding and re-epoxying the break line, but it becomes a permanent week point and breaks at the spot of the repair.
I also tried cutting the fin off completely, making a new fin slot, and epoxying another fin right next to the broken one (I inner-fillet my HP rockets, so the root of the fin wont come out). That worked better, but produced an unbalanced booster, which was also not great.

Good luck with yours!

a
 
The only successful path to repairing broken ply fins is fiber-glassing over them.

I did try sanding and re-epoxying the break line, but it becomes a permanent week point and breaks at the spot of the repair.
I also tried cutting the fin off completely, making a new fin slot, and epoxying another fin right next to the broken one (I inner-fillet my HP rockets, so the root of the fin wont come out). That worked better, but produced an unbalanced booster, which was also not great.

Good luck with yours!

a

Heaven help an unbalanced booster. I can definitely relate to that.
 
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