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Punkin Chunkin 2010 Mythbusters Episode

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Punkin Chunkin 2010 Mythbusters Episode

Unread postAuthor: omniscient » Thu Nov 25, 2010 10:58 pm

Is anyone here going to watch this show tonight? Or, has anyone watched it, already? Comes on in 3 minutes, for me!
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Unread postAuthor: Gun Freak » Fri Nov 26, 2010 12:42 pm

I watched it! It was so awsome! Those air cannons launched pumpkins like 3/4 of a mile! Wow. Those were some huge machines. It was cool, but I missed the first hour. I watched it at 9.
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Unread postAuthor: SpudFarm » Fri Nov 26, 2010 2:14 pm

What season and episode was this broardcasted on?
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Unread postAuthor: JDP12 » Fri Nov 26, 2010 3:29 pm

it was sweet! It was on science channel
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Unread postAuthor: Gun Freak » Fri Nov 26, 2010 4:32 pm

It was also aired on Discovery.
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Unread postAuthor: clemsonguy1125 » Fri Nov 26, 2010 4:47 pm

I watched it at 11 on discovery, missed air cannon round one though. I wonder what type of valve they used. I assume it was a slow opening valve so they would not make pumpkin pie. Maybe a large butterfly valve or diaphram valve.
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Unread postAuthor: omniscient » Sun Nov 28, 2010 1:01 am

clemsonguy1125 wrote:I watched it at 11 on discovery, missed air cannon round one though. I wonder what type of valve they used. I assume it was a slow opening valve so they would not make pumpkin pie. Maybe a large butterfly valve or diaphram valve.


As far as construction is concerned, I found this link :
<a href="http://www.popsci.com/gadgets/article/2010-01/air-cannon-sends-pumpkins-3700-feet">How it Works: The Artillery-Grade 600 MPH Pumpkin Cannon</a>

This cannon does, in fact, use a butterfly valve.
Using a generic I.d. of exactly 10", a 100-foot long barrel would have a volume of 94,247.78 cubic inches ( 408 gallons )

This cannon has twin 1,000 gallon modified propane tanks as air reservoirs,
so the C:B ratio is approximately 4.9:1

I've watched this show and now wonder if a ported muzzle and even a muzzle brake would help to eliminate the chance of the pumpkin grenading as it exited the barrel. (What they refer to as "pumpkin pie")
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Unread postAuthor: jackssmirkingrevenge » Sun Nov 28, 2010 1:11 am

omniscient wrote:This cannon does, in fact, use a butterfly valve.


A burst disk could be simpler to implement, and allow them to achieve the same performance with much less pressure (because unlike the butterfly valve, you have almost instant full flow with virtually zero opening time) and reduce the chances of the pumpkin being destroyed.

I've watched this show and now wonder if a ported muzzle and even a muzzle brake would help to eliminate the chance of the pumpkin grenading as it exited the barrel. (What they refer to as "pumpkin pie")


I don't think anything at the muzzle would help, the pumpkin is usually destroyed by the "impact" of the air burst and sudden acceleration, it would be "pumpkin pie" long before it reached the muzzle.
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Unread postAuthor: omniscient » Sun Nov 28, 2010 2:13 am

jackssmirkingrevenge wrote:
omniscient wrote:This cannon does, in fact, use a butterfly valve.


A burst disk could be simpler to implement, and allow them to achieve the same performance with much less pressure (because unlike the butterfly valve, you have almost instant full flow with virtually zero opening time) and reduce the chances of the pumpkin being destroyed.

I've watched this show and now wonder if a ported muzzle and even a muzzle brake would help to eliminate the chance of the pumpkin grenading as it exited the barrel. (What they refer to as "pumpkin pie")


I don't think anything at the muzzle would help, the pumpkin is usually destroyed by the "impact" of the air burst and sudden acceleration, it would be "pumpkin pie" long before it reached the muzzle.


...Good point about the about the impact of the air burst and sudden acceleration.

The idea of a burst disc, though... even one that remains in a fixed position and scored to split open... wouldn't there be some tiny fragments of material that would blast into the center of the pumpkin, as well as the sudden and violent rush of air direct right into the center of the barrel, would probably be much more likely to grenade the pumpkin?

Too bad that they probably would not allow the pumpkins to be frozen, thus increasing the density of it's center mass? IIRC, they do not allow any type of wadding. You would think that a 5-foot long foam plug would work great and finally allow one to break the 1-mile mark?
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Unread postAuthor: jackssmirkingrevenge » Sun Nov 28, 2010 3:28 am

omniscient wrote:The idea of a burst disc, though... even one that remains in a fixed position and scored to split open... wouldn't there be some tiny fragments of material that would blast into the center of the pumpkin, as well as the sudden and violent rush of air direct right into the center of the barrel, would probably be much more likely to grenade the pumpkin?


used at the same pressure, of course the burst disk would be more than likely to shatter the pumpkin - but the point is that since you have a much more efficient valve, you can do more with less. I wouldn't think the burst disk fragments would be particularly damaging.

Too bad that they probably would not allow the pumpkins to be frozen, thus increasing the density of it's center mass? IIRC, they do not allow any type of wadding. You would think that a 5-foot long foam plug would work great and finally allow one to break the 1-mile mark?


How would freezing the pumpkin increase its density, unless you filled it with water first? If anything, ice is less dense than water ;)

What if you made a sabot that didn't exit the barrel, along these lines?. Would it be legal? Or if not, would anyone check :D
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Unread postAuthor: Gun Freak » Sun Nov 28, 2010 9:48 am

@Jack, this might answer your question. I'm too lazy to check though :D

Edit, I was feeling generous :)
1. All pumpkins fired must remain intact until they impact the ground to obtain an official measurement.
2. No part of the machine shall cross the firing line.
3. No Wadding (including bean chaff, straw, foam, metal, or any other object.)
4. No explosives are allowed.
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Unread postAuthor: jackssmirkingrevenge » Sun Nov 28, 2010 10:30 am

But technically a captive piston is not wadding, it's an air powered catapult... of sorts... hmmm...
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Unread postAuthor: saefroch » Sun Nov 28, 2010 11:45 am

jackssmirkingrevenge wrote:But technically a captive piston is not wadding, it's an air powered catapult... of sorts... hmmm...
I'd just be concerned about actually managing to catch the piston at the end of travel... the forces on it must be huge.

jackssmirkingrevenge wrote:used at the same pressure, of course the burst disk would be more than likely to shatter the pumpkin - but the point is that since you have a much more efficient valve, you can do more with less
The reason I think a slow valve at higher pressure is better than a fast valve at lower pressure is the lack of a pressure gradient as the pumpkin travels down the barrel.

Also keep in mind those pumpkins are specially grown for shooting, they probably contain almost not seeds and are almost all very hard flesh. Freezing them might even make them more fragile.
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Unread postAuthor: Big-E » Sun Nov 28, 2010 11:49 am

Hmm I wonder if it would be against the rules to cultivate the pumpkins in a length of your barrel material, so you end upwith perfectly formed "Pumpkin slugs...
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Unread postAuthor: jackssmirkingrevenge » Sun Nov 28, 2010 11:51 am

saefroch wrote:I'd just be concerned about actually managing to catch the piston at the end of travel... the forces on it must be huge.


Been done...

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