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Projectile Stabilization

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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Projectile Stabilization

Unread postAuthor: PVC Arsenal 17 » Fri Nov 27, 2009 11:26 pm

I'm interested in shooting this:

Image

Out of a spud gun such that the nail sticks into a wooden target.

What is it?

It's the piercing bolt I used in my 12 gram launcher. Seeing as that thing ripped itself apart and I'm too lazy to build a copper one, I have no use for the bolt. But... I remembered that it fits well into 1" sch40 pvc so why not launch it?

It weighs about 122 grams. Length is about 2.3" not counting the nail. Diameter is 1".

I've thought of using a simple streamer, fixing a tail section of an arrow to the back, and fixing a blowgun dart shaft & cone to the back.

Image

I liked the idea of a streamer the best, it's easy enough to drill a hole in the back of the thing and thread in an eye screw. The actual streamer is the hard part. I'm not sure that a simple string could stabilize something this heavy and prone to tumbling. I may need to connect a light ball to the end of the string to increase drag.

Any ideas?
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Unread postAuthor: VH_man » Fri Nov 27, 2009 11:50 pm

I really would hate to see a streamer put on something so beautiful. Streamers are prone to high levels of drag. They are used in lightweight rockets to give them 'tumble' recovery.

If it was me, I would put a long stick out the back of it, and attach some fins to that. The general rule of thumb (for me at least) when it comes to stability is to have someone pick it up and be surprised at it's center of gravity.

Another way to test is to tie a string around the center of gravity (the balance point) and then swing it around your head on a long string. when the projectile flies true (perfectly straight, even when started backwards) your round has reached stability.
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Unread postAuthor: PVC Arsenal 17 » Sat Nov 28, 2009 12:13 am

Might have to take the nail out to do the CG test. :lol:

My only problem with adding a long finned stick out the back is that doing so would create heaps of dead space in the barrel as well as reduce the effective length of the barrel.

I'm going to play around with some ideas tomorrow.
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Unread postAuthor: Gippeto » Sat Nov 28, 2009 1:22 am

As typical spuddy ranges are measured in "10's" of feet at best, I don't think velocity loss due to excess drag is too much of a problem.

KISS...I vote streamer. :) 2-3' of 1/4" poly rope?
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Unread postAuthor: skyjive » Sat Nov 28, 2009 1:36 am

I doubt a streamer would stabilize such a big projectile. I think the blowgun dart tail would work better, although honestly any heavy uniform density cylinder like that is pretty much gonna do its own thing short of a big parachute coming off the back. Any chance of hollowing out the tail or something?
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Unread postAuthor: POLAND_SPUD » Sat Nov 28, 2009 4:18 am

I have an idea for stabilizing projectiles...

take a small DC motor with a battery and put a heavy cylinder on its shaft... it should act as a gyro... then just put the thing into a small section of PVC pipe and strap it to the projectile

what do you think guys would it be strong enough to stabilize a large round ?
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Last edited by POLAND_SPUD on Sat Nov 28, 2009 6:13 am, edited 1 time in total.
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Unread postAuthor: jackssmirkingrevenge » Sat Nov 28, 2009 5:14 am

POLAND_SPUD wrote:take a small DC motor wit ha battery and put a heavy cylinder on it's shaft... it should act as a gyro... then just put the thing into a small section of PVC pipe and strap it to the projectile


Why not have the motor mounted on coaxial bearings and spin that up?
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Unread postAuthor: POLAND_SPUD » Sat Nov 28, 2009 5:57 am

ohhh yeah that makes sense... I think it would be easier to spin the projectile not the motor... of course it's all about finding a small but powerful motor and making sure that ieverythign is perfectly balanced... otherwise it might be hard to achieve high RPM


hmmm... I've got a better idea.... you can put coils around the pipe and and mount magnets on the projectile... that will turn it into a brushless motor
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Unread postAuthor: PVC Arsenal 17 » Sat Nov 28, 2009 1:07 pm

I had very good results using a .625 blowgun dart shaft & cone. So far I tested it out to 50 feet and it was surprisingly accurate. No tumbling whatsoever. The problem is that the dart shaft gets bent due to the force of the impact so reusing the slug is a pain in the ass. I'm going to try streamers next.
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Unread postAuthor: psycix » Sat Nov 28, 2009 2:26 pm

Just add anything that could perform as a tail.
Duct tape, a piece of rope or something else works fine for stabilization.
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Unread postAuthor: McCoytheGreater » Tue Dec 15, 2009 2:14 pm

Have you thought of rifling the slug? Dremel tooling seven or eight grooves into the side of the slug at an angle doesn't seem like it would be too difficult. Getting the angles right would be the problem. "What about gasses escaping through the rifling? Ahhh...only dremel the grooves to about a quarter inch of the end of the barrel seal. That sounds legit to me.
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Unread postAuthor: jackssmirkingrevenge » Tue Dec 15, 2009 2:30 pm

McCoytheGreater wrote:Have you thought of rifling the slug? Dremel tooling seven or eight grooves into the side of the slug at an angle doesn't seem like it would be too difficult.


*cough*

They would have to be some pretty substantial grooves if there are to have any effect...
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Unread postAuthor: McCoytheGreater » Tue Dec 15, 2009 2:41 pm

Well yeah, but it should still work, right? How long is the barrel you are using?
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Unread postAuthor: jackssmirkingrevenge » Tue Dec 15, 2009 2:46 pm

McCoytheGreater wrote:Well yeah, but it should still work, right?


Not really. The point of rifled slugs is to enable them to squeeze through a shotgun's choke.

Take this Brenneke rifled slug as an example:

Image

As you can see it's attached to a lightweight fibre tail, meaning in reality it flies straight because it's drag stabilised in the same way that a shuttlecock is.
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Unread postAuthor: McCoytheGreater » Tue Dec 15, 2009 2:58 pm

I've been an avid sport shooter 14 years now. That fiber tail is the wadding. The rifling is what spins the slug down the smooth bore of the shotgun. And unless the shotgun has a cylinder barrel (one without a choke tube) then slugs aren't really the safest things to be shooting out of the shotgun. Either way. A little spin on the slug from gun shouldn't hurt.
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