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Do spuds tumble?

A place to ask general spud cannon related questions.
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Do spuds tumble?

Unread postAuthor: boyntonstu » Wed Jan 27, 2010 11:26 am

I never shot a spud, carrot, or any other vegetable.

I wonder how far they go before/if they tumble?

IOW How far do they fly straight?

What length to diameter ratio makes them stable?
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Unread postAuthor: inonickname » Wed Jan 27, 2010 11:34 am

They are not stable in any sense of the word. They will most likely begin tumbling within a few of their own lengths. "Accurate" flight won't be sustained for long at all (not that spudguns have ever been intended to be sub MOA shooters). As for length/diameter that makes them stable, I doubt there is one.
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Unread postAuthor: McCoytheGreater » Wed Jan 27, 2010 11:55 am

inonickname wrote:They are not stable in any sense of the word. They will most likely begin tumbling within a few of their own lengths. "Accurate" flight won't be sustained for long at all (not that spudguns have ever been intended to be sub MOA shooters). As for length/diameter that makes them stable, I doubt there is one.



Agreed. Unless you can cut tail fins into the spud, then you won't be able to stabilize it in flight. Spuds might go 5 feet before they start to tumble, that is, if they don't start right out of the barrel. I usually try to cut the spud length to the diameter of the barrel that way when it does tumble the air resistance on the front and sides of the projectile will be closer.
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Unread postAuthor: jackssmirkingrevenge » Wed Jan 27, 2010 12:35 pm

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Unread postAuthor: McCoytheGreater » Wed Jan 27, 2010 2:26 pm

I did not realize your high speed camera worked that well, JSR. :D
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Unread postAuthor: jackssmirkingrevenge » Wed Jan 27, 2010 2:55 pm

If only we could get that sort of performance for $200 :roll: still, 1000 fps at that price was simply unheard of 10 years ago, who knows what our spudding grandchildren will enjoy :)
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Re: Do spuds tumble?

Unread postAuthor: McCoytheGreater » Wed Jan 27, 2010 3:41 pm

boyntonstu wrote:I never shot a spud, carrot, or any other vegetable.


While not shooting these things is very morally responsible of you, I would recommend launching some spuds to get a "feel for it." The first time is always the hardest, but after that it comes easy.

That aside, I've found that carrots work rather well if your bore is small enough to get a good seal. Be sure that the carrot head is the first to exit as the skinny end will act as a stabilizer of sorts.
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Re: Do spuds tumble?

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Re: Do spuds tumble?

Unread postAuthor: Ragnarok » Wed Jan 27, 2010 5:42 pm

boyntonstu wrote:I wonder how far they go before/if they tumble?

Very dependent on the launcher and muzzle blast. If I fire a spud from HEAL, you can sometimes see it suddenly fly apart about 20-30 metres from the muzzle from the sheer forces involved with its tumbling. It also slows down a lot as a result.

Quite a cool "airburst" effect though when it happens.

Do the same thing with the porting attachment (to reduce the muzzle blast), and it can remain surprisingly stable for quite long distances from the muzzle. Most of the time, you can't see the damn thing at all - it's too far away to see before your eyes can catch up.
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Unread postAuthor: jimmy101 » Wed Jan 27, 2010 6:03 pm

There's an old truism;

"Any simple symmetric shapes of uniform density is unstable in flight".

So, all cylinders, spheres, cubes, cones ... are unstable. "Bullet" shape is unstable.

To get a shape to be stable you generally need to either add fins or make it of non-constant density (like a solid nose with an empty cylinder for the tail).

Spinning of course also stabilizes a projectile.

I've got a simple pneumatic that I've fired shells made from 3/4 inch copper pipe with end caps. Nothing was done to deal with the muzzle effects. Shooting at plywood the round has turned perpendicular within about 2' of the muzzle. (As indicated by rectangular instead of round holes in plywood.)

One common misconception is that tumbling leads to inaccuracy. That is not true. Variable tumbling leads to inaccuracy. If you can get a round to tumble the same way every time then it will be much more accurate. Flatline paintball barrels as well as hopups increase accuracy somewhat since the rounds are given consistent spins. The spin itself doesn't stabilize a spherical round. The consistent spin makes the drag consistent from shot to shot.
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Unread postAuthor: Insomniac » Wed Jan 27, 2010 6:17 pm

jimmy101 wrote:There's an old truism;

"Any simple symmetric shapes of uniform density is unstable in flight".

So, all cylinders, spheres, cubes, cones ... are unstable. "Bullet" shape is unstable.

To get a shape to be stable you generally need to either add fins or make it of non-constant density (like a solid nose with an empty cylinder for the tail)


I'm not sure if this counts, but a long, hollow cone with walls of consistent thickness will be stable in flight, due to the fact that while it's center of gravity will sit roughly in the middle, the center of pressure will tend to be somewhat furthur back.

I suppose this is cheating though as it's using a hollow space to make it's density vary along it's length.
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Unread postAuthor: Techie » Wed Jan 27, 2010 7:10 pm

jackssmirkingrevenge wrote:Videos speak better than words ;)

lets see.....
A picture is worth 1,000 words. That video is at 1000 or so fps, and 21 seconds long.....its worth quite alot at 21,000,000 o.O
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Unread postAuthor: Insomniac » Wed Jan 27, 2010 7:27 pm

Techie wrote:
jackssmirkingrevenge wrote:Videos speak better than words ;)

lets see.....
A picture is worth 1,000 words. That video is at 1000 or so fps, and 21 seconds long.....its worth quite alot at 21,000,000 o.O


Not quite... It was recorded at 1000ish fps, but only plays back at 30ish...

So it's only worth about 630000 words :wink:
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Unread postAuthor: Techie » Wed Jan 27, 2010 7:47 pm

Insomniac wrote:
Techie wrote:
jackssmirkingrevenge wrote:Videos speak better than words ;)

lets see.....
A picture is worth 1,000 words. That video is at 1000 or so fps, and 21 seconds long.....its worth quite alot at 21,000,000 o.O


Not quite... It was recorded at 1000ish fps, but only plays back at 30ish...

So it's only worth about 630000 words :wink:

i guess ya got me there =P
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Unread postAuthor: jackssmirkingrevenge » Thu Jan 28, 2010 1:08 am

Techie wrote:That video is at 1000 or so fps


I'd wager it's at least 10 times that, assuming it's a military testing range.
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Unread postAuthor: Techie » Thu Jan 28, 2010 6:36 pm

jackssmirkingrevenge wrote:
Techie wrote:That video is at 1000 or so fps


I'd wager it's at least 10 times that, assuming it's a military testing range.

probably so, didn't thank about that. ill probably be shot one day because i didn't think my assailants gun actually shot bullets
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