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Retractable fins

Post about things you have launched or thought about launching. Also post about various materials used for building cannons. No posts about explosive projectiles!
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Retractable fins

Unread postAuthor: daccel » Tue Apr 15, 2008 8:09 pm

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?
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Unread postAuthor: Sticky_Tape » Tue Apr 15, 2008 8:13 pm

That's a cool Idea Me liky.
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You can tell how awesome a cannon is by the pressure used.
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Unread postAuthor: OuchProgramme » Tue Apr 15, 2008 8:28 pm

DYI had a steel projectile w/ -i believe i'm correct-, alluminum fins.
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Unread postAuthor: VH_man » Tue Apr 15, 2008 8:31 pm

Take a look at the

"HIGH EXPLOSIVE 12 GUAGE GRENADES"

these little buggers use retractable fins that open upon leaving the barrel... they are pretty darn accurate from what ive seen on youtube

This is actually a good idea.... finned projectiles are pretty darn accurate.
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Unread postAuthor: daccel » Tue Apr 15, 2008 8:36 pm

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 :lol:. Attached pic.

Edit 2: Now it will work in a normal barrel. See 2nd pic.
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Unread postAuthor: OuchProgramme » Tue Apr 15, 2008 11:04 pm

Hmm...the fins look a little bit floppy. If you're aiming for high velocity, the fins aren't going to do very much.

Have fins which curl up against the sides of the wall so you get some spin-Fin directions-

And then fire it w/ a sabot.
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Unread postAuthor: Blitz » Wed Apr 16, 2008 12:12 am

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).

Image
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Unread postAuthor: Eddbot » Wed Apr 16, 2008 12:53 am

Blitz, is that an actual round that gets shot out of something?
if so, where and how much?
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Unread postAuthor: Blitz » Wed Apr 16, 2008 1:02 am

Yes, it's a fragmentation grenade, 12-gauge -- called the FRAG-12. Read this for a factsheet.
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Unread postAuthor: jackssmirkingrevenge » Wed Apr 16, 2008 1:23 am

Eddbot wrote:Blitz, is that an actual round that gets shot out of something?


Here's the FRAG-12 leaving the AA12 automatic shotgunat a rate of 6 rounds per second :D

[youtube]http://youtube.com/watch?v=cQYp9fOJ9VI[/youtube]
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Unread postAuthor: XxtriviumxX » Wed Apr 16, 2008 3:55 am

Woah carnage :D...

Well daccel's got a pretty cool idea there, but how could you make retractible fins which fold sideways?... Without buying them that is. :D
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Unread postAuthor: VH_man » Wed Apr 16, 2008 5:33 am

hahah yes thats what i was talking about.... that thing in quotations was supposed to be a link. pretty sweet eh?
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Unread postAuthor: VH_man » Wed Apr 16, 2008 5:39 am

Blitz wrote: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).

Image


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 :D

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.
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Unread postAuthor: jackssmirkingrevenge » Thu Apr 17, 2008 2:49 am

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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Unread postAuthor: TwitchTheAussie » Thu Apr 17, 2008 6:58 am

VH_man wrote:Making fins like that i think is out of the question for us spudgunners......


Bet if I had the tools I could probably make fins like that. Its easy with the right metals and an oxy torch :D
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