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Fastest Potato Velocity?

A place to ask general spud cannon related questions.
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Unread postAuthor: Fnord » Sun Apr 15, 2007 9:20 am

...but is it LOUD? :)

Set up some kind of a shock scale for a target and caculate the muzzle energy and velocity you get that way. It will probably be innacurate, but will give you numbers that are close enough to the chrony to prove/disprove what is happening
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Unread postAuthor: jackssmirkingrevenge » Sun Apr 15, 2007 9:26 am

Your chrony's broken :?
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Unread postAuthor: super spuder » Sun Apr 15, 2007 10:44 am

i do believe that he has already said that his chrony's not broken. why couldn't a potato go 2700 fps. 1- it is a hybrid 2 it is a 4 x mix. 3 it has a 50 foot barrel on it . and who cares what those computer programmes say they are an estimate and they can be wildly off. i am not saying it can and i am not saying it cant. but if he says it can go 2700 fps i will belive him until i can see some actual proof that it cant.
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Unread postAuthor: jackssmirkingrevenge » Sun Apr 15, 2007 10:55 am

Forgive me but I'm a bit skeptical.

This will propell a tiny bullet to 2700 feet per second from a barrel less than 2 feet long, but that's with 58,000 psi of chamber pressure...

Have you tried chronying it with a solid projectile that isn't prone to disintegrating if fired at such a high velocity?
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Unread postAuthor: super spuder » Sun Apr 15, 2007 11:13 am

i duno. i cant wait to see a video of it in the contest
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Unread postAuthor: Hotwired » Sun Apr 15, 2007 11:13 am

This could be a record breaker but theres at least two things to do to confirm it:

Dry firing.

Firing with an equal mass projectile that will not disintegrate - wood or plastic perhaps.
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Unread postAuthor: jimmy101 » Sun Apr 15, 2007 11:56 am

_Fnord asked a very relevant question... was it loud? A mach 2+ round should give one hell of a sonic boom.

I'm skeptical, but from the description this is one hell of a big hyrbid. I don't know that any of the models of spud guns are applicable since none of the guns used to calibrate the models are capable of velocities anywhere near what is claimed. I wouldn't think EVBEC or GGDT would be of much use modeling the internal ballistics of a supersonic spud.

I think you really need an independent measure of the velocity. Chrony's are touchy devices and use an extremely weak signal to detect the round passing over the gates. It is possible that the shock wave (sound wave) is causing the chrony to trigger at the wrong time.

A couple of thoughts, a supersonic spud fired straight up should have a huge hang time. You <strike>can</strike> cannot calculate an accurate muzzle velocity from hang time data but the hang time should be much larger than what a typical spud gun does. If you get a 10 to 20 second hang time the spud is no where near supersonic.

Another possibility is to setup a microphone some distance out from the barrel. I would think there is a positioning of the microphone that should give to bangs in the recording; the sound of the gun going off and the sonic boom of the projectile passing the mic. If the spud is really going mach 2 then the sonic boom of the spud will get to the mic before the sound of the gun. You would have to be careful of echoes though, you don't want any large surfaces around that could give an echo of the sound of the gun firing.

EDIT: Said "can" when I meant "can not"
EIT 2: To fix what I screwed up on Edit 1.
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Last edited by jimmy101 on Sun Apr 15, 2007 12:27 pm, edited 1 time in total.
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Unread postAuthor: homedepotpro » Sun Apr 15, 2007 12:15 pm

jimmy101 wrote:_Fnord asked a very relevant question... was it loud? A mach 2+ round should give one hell of a sonic boom.



A couple of thoughts, a supersonic spud fired straight up should have a huge hang time. You <strike>can</stricke> cannot calculate an accurate muzzle velocity from hang time data but the hang time should be much larger than what a typical spud gun does. If you get a 10 to 20 second hang time the spud is no where near supersonic.




there are many problems with that vertical shot. the spud is traveling supposedly mach 2, how are you going to track that. the gun has a 50 foot barrel, how is that going to be supported. plus if you shot something that high up there is no telling where it will land and how much damage it will do.
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Unread postAuthor: Velocity » Sun Apr 15, 2007 12:20 pm

Even if the hybrid does not shoot 2700 FPS, I think we have a shoe in for the cannon competition winner :lol: . Initially I was assured that this issue was total BS, and that killjoy was lying or serious miscalculating; but after hearing the size of the gun... well.

I am going to remain skeptical, neither believing it can or being sure that it can't. Because if a common spudgun was to reach 2700 FPS, this would be the one to do it :wink:
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Unread postAuthor: Killjoy » Sun Apr 15, 2007 12:26 pm

Well the potato was actually half a potato (so that it was about 3"long and weighed +-4 ounces) so it was lighter then a regular potato.

And I dry fired it the first day of test fires just to make sure it was working and nothing unuasul would happen with the chrony, and the chrony displayed no recorded velocity and no error messages, and that was when it was 2 feet away from the muzzle.

I will try using a solid projectile of equal mass and weight though when i get another chance to test fire it agian, which should be in a couple weeks.
And yeah, it is loud.
Edit:
thanks rmich
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Unread postAuthor: jimmy101 » Sun Apr 15, 2007 12:38 pm

Homedepotpro: You are right, pointing a gun that long straight up would be a challenge.

But, the spud won't do much damage on the way back down. Well, more precisely, the damage it'll do has very little to do with a 500 FPS versus 2000 fps muzzle velocity. In both cases, the speed that the spud hits the ground will be it's terminal velocity. For a spud that is only about 100 fps.

Baseballs and golf balls both have terminal velocities of about 105 fps.

You can probably throw a spud at ~100 fps so it won't do that much damage.
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Unread postAuthor: sandman » Sun Apr 15, 2007 8:29 pm

ok put a large piece of paper in front of the chrony, and fire through that and then i will beleive
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Unread postAuthor: Killjoy » Sun Apr 15, 2007 10:11 pm

Why put the paper in front? to prove that it was actually the potato that exited the barrel and traveled out and was picked up by the chrony?
I already know that the potato exited the barrel in one peice because i had a 1/4" thick piece of plywood behind the chrony and the potato nailed it dead center and left a hole that was exctly the size of the potato, so i have no doubt the potato actaully exited the barrel in one peice and was picked up by the chrony.
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Unread postAuthor: joannaardway » Mon Apr 16, 2007 4:26 am

Doing a little maths, and neglecting pressure effects in the barrel, the acceleration would need to be an average of 2060 G to get 2700 fps from a 55 foot barrel - entirely possible even for a fairly modest pneumatic to display, let alone a 4x hybrid.

I have never seen 2000 G destroy a potato before, so we can be fairly sure that the same applies here, and the spud was at least fairly intact.

Assuming 2" long potato slug (for these purposes, the exact barrel ID and mass do not matter - the area [and thus the force from the pressure] and mass are in direct proportion), then an average pressure of about 16 bar (230 psi) would be needed.

AFAIK, that's more than possible for a 4x hybrid.

Pressure effects are another matter though. I can't be bothered to determine the exact results now, but I'm not that hesitant to believe that the velocity is possible from something 55 feet long.

All of you who are sceptical, then I'm not forcing you to change your mind, but it is way more than possible for it to happen.

I can't wait to see damage pictures though!
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Unread postAuthor: CpTn_lAw » Mon Apr 16, 2007 5:07 am

this is quite amazing!! 2700 fps.......822 m/s...that's the velocity of a rifle bullet. 34,000 joules of kinetic energy if the potato weights 100 grams.
this is near the energy of a DCA bullet. So, don't underestimate the power it has. be careful, a DCA bulet shot at a house will go through. Considering the potato will explode when hitting, all the energy will be transfered to the bits and the wall...still leaves a hell of energy to be dissipated in the wall...

Well, if all your numbers are right, then congrats mate, you've established the new potato-velocity world record !!!!!! :o :o
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