Posted: 04/15/2008 19:09 PM Post subject: Retractable fins
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Joined: 11 Oct 2007 Posts: 45 193.06 Spud Bux
I was thinking today about how to make fin stabilized ammo that would be accurate and cheap, and doesn't need a sabot, and came up with this.
It uses a cheap retractable ball point pen and fins cut from throwing dart fins. Obviously the front would have to be weighted, and spring glued to both parts of the pen. The fins would have to be folded to insert into the barrel or pressed into the pen to put in a magazine. As the dart is accelerated the center part is pushed in which folds the fins in narrower than the bore so that on exit the dart isn't pushed in one direction or another by one fin catching slightly or springing open more.
Is there enough potential inaccuracy generated by having the fins spring open immediately as they leave the barrel, as in the other designs for folding fins, to merit this design?
I don't know how I didn't think of this before! If you retain the 'clicking' (is there a term for this?) mechanism, you could retract the fins before inserting, then the acceleration would press the ink part forward and after the body had left the barrel the fins would pop out.
Forgot to add, obviously the air itself wouldn't push the ink part forward, I was thinking of using it in this cannon, where there is a piston in the barrel to do that.
Edit 1: Woohoo! it works. You'll have to forgive my enthusiasm, I had one of those eureka moments . Attached pic.
Edit 2: Now it will work in a normal barrel. See 2nd pic.
retractable fins2.jpg
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Last edited by daccel on 04/15/2008 22:05 PM; edited 1 time in total
This is what I'd rather do, have them fold sideways, as opposed to coaxial with the projectile (Come to think of it, this is what VH_man was referring to).
This is what I'd rather do, have them fold sideways, as opposed to coaxial with the projectile (Come to think of it, this is what VH_man was referring to).
Yes that is what i was talking about....... thank you for finding that.
I personally like the shape of the fins, notice how they are Airfoil shaped as so to impart a spin on the grenade
Making fins like that i think is out of the question for us spudgunners......
personally id rather use Blowgun style fins on the dart, seeing as they double as their own wadding.
I think in the case of us humble amateurs, it's not really worth the trouble. Fold-out fins are undeniably cool, but you never get to see them work and you can achieve the same stability by simply hollowing out the tail of your projectile.
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. Attached pic.
