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Finned Projectiles

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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Finned Projectiles

Unread postAuthor: Mountain Storm » Sun Oct 24, 2010 9:41 pm

I have built 3 types of finned projectiles so far and at least one of them works as planned :wink:

For night launches I built an acrylic projectile that holds a glow stick.
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It flies erratically. I think that the fin surface is too small to make enough drag, and the weight of the payload shifts the CG back too far. Here is the thread on that one. http://www.spudfiles.com/forums/glowing ... 21879.html

Here's the one I think is going to be worth making again and again.
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I was amazed at how far straight up this one went. It went at least twice as high as anything I've shot from the spud chucker so far. I estimate around 1000ft. I lost it in the tall grass after 4 shots so I made another (pictured above). I use polycarbonate for the fins and fit them into a hole I bore in the wood potato I made by stacking three disks of 3/4" together and shaping them with the router. Unlike many of the projectiles I've tested this one consistently flies straight...no wobble, no tumble. And it falls to earth the same way hard enough to bury itself in the dirt about an inch.

I've made templates to reproduce the fins, but it still takes a little work to get them made so I was looking for something easier/faster to make that would accomplish the same task.

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This one I did not get to launch. I neglected to test fit it and it was too snug in the bore and ended up blowing the cannon apart when it refused to launch. I then beat it apart trying to get it out of the bore.

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I just cut and notched two pieces of aluminum sheet and fit them together to form the fins and thin I slit the aluminum tube on the bandsaw and hammered the fins into the slits. Talk about fast...less than 5 minutes to make a tail assembly for one of the wooden potatoes.

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I really want to test this one out. I think the square fins will have the right amount of drag. I used a 3" section of tube and 1" fins as wide as the bore (approximately 1-5/8" diameter bore).

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With a tight fitting hole the tube stays in place with no glue or fasteners. The reason it's broken is from me ramming the fins repeatedly to force the stuck projectile from the bore.

Once I get the cannon repaired I'll make another and give it a test flight.

What do you think about my finned projectiles?
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Unread postAuthor: jackssmirkingrevenge » Sun Oct 24, 2010 10:11 pm

For even better performance you can eliminate the full bore nose and use a separate sabot to seal, this will greatly decrease drag and increase sectional density, something like this:

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Unread postAuthor: jrrdw » Mon Oct 25, 2010 7:46 am

Your the 1st member that I can remember to make 'wooden potato's'...nice! :P

I've built 50 or so Estae's model rockets and in doing so learned about steady flight. I've built many style fins and by far the best flying rockets were the one's with 1 fin placed on the body at a angle. It always put major amounts of spin on the rocket. The wobble would disappear with in the 1st 100 feet or so. Keep in mind model rocket's accelerate slowly...

You might want to give that a try just for kicks. I see your using a few different materials for fines, balsa wood holds up surprisingly well when painted with enamel paint.
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