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Twitches Science Project V.2. "SNCA"

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Twitches Science Project V.2. "SNCA"

Unread postAuthor: TwitchTheAussie » Tue Jul 24, 2007 2:16 am

Well ever since V.1 "Whompah Stompah" blew up from an attack of MAPP gas, I decided to rebuild it. V.2 is finished. I gave it the name "Spray and Click Affair" because thats basically what it is :lol: Anyway its just a basic cannon, piezo lighter and a fan. I screwed everything together so it wont separate after every shot, and epoxied it all up.

Had to give a demo today so that went good. Got 150+m with a cut up rubber ball and it gave me good marks just because it outshot the ballista a kid entered.

My problem is this. Being an avid shooter I know what a sonic boom sounds like and my cannon made one. Normally at most combustions make 30-40 psi and my c:b ration is a bit off bout 3:1 and despite the ball being wedged in tight barely halfway down the barrel but it still made a sonic boom.

How is this possible?
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Unread postAuthor: hi » Tue Jul 24, 2007 2:33 am

my guess is that the gas expanding is the sonic boom and not the rubber ball it self.
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Unread postAuthor: TwitchTheAussie » Tue Jul 24, 2007 3:04 am

Thats what I thought thanks man :P
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Unread postAuthor: f.c » Tue Jul 24, 2007 3:22 am

you got to make a potato cannon for a science project. nice.
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Unread postAuthor: Fnord » Tue Jul 24, 2007 6:29 am

They let you build a gun for a science project in australia? Are they illegal where you live?
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Unread postAuthor: spud yeti » Tue Jul 24, 2007 8:44 am

youre really lucky to have the excuse to build a cannon as a school project! As hi said, its probably just the gas, not the projectile(unfortunately!). Good luck for it, and I hope you get good marks 8)
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really good quote/phrase here
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Unread postAuthor: frankrede » Tue Jul 24, 2007 2:11 pm

How sure are you that you broke the sound barrier?
Chronograph?
I doubt that a run of the mill cannon with a bad C/B and a poorly fitted ammo would break the sound barrier.
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Unread postAuthor: TwitchTheAussie » Wed Jul 25, 2007 1:44 am

The ammo fitted pretty tightly and Ive grown up around guns so I do know what sound something makes when it breaks the sound barrier Frank. And the cops let me off lightly just because I had an official note from the school saying I could make one.
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Unread postAuthor: jimmy101 » Wed Jul 25, 2007 1:49 pm

Not a chance that you broke the sound barrier.

You can not tell how fast a round is going by just the sound. A very experienced shooter might be able to tell after firing many rounds of a particular caliber and varying loads and chrono'ing every shot. But, that knowledge would be completely useless when it came to a round as different as a "rubber ball". He would have to go through the entire process with the new round; multiple shots, varrying loads and a chrony, to learn what supersonic sounds like for the new round.

A spud gun does not have to be supersonic to make a hell of a lot of noise. A large CB ratio will make the gun much louder than it would be with a more reasonable CB. The sound you heard was nothing more than the "bang" of the gun itself.
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Unread postAuthor: TwitchTheAussie » Thu Jul 26, 2007 4:12 am

I never said it was the ball. I was just confused about how gases at 30-40 psi could break the sound barrier. Once again I will say in bold I know it wasnt the rubber ball I was just confused about how gases at 30-40 psi could break the sound barrier. I know Im not making much sense but I have personal reasons for it.

I just didnt think 30-40 psi would break the sound barrier by itself.
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Unread postAuthor: Modderxtrordanare » Thu Jul 26, 2007 4:42 am

You didn't break the sound barrier.
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Unread postAuthor: wannabie » Thu Jul 26, 2007 4:57 am

i agree with modder i highly doubt that you broke the sound barrier.... sorry to break your bubble lol
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Unread postAuthor: jackssmirkingrevenge » Thu Jul 26, 2007 5:30 am

30-40 psi is 15-25 psi more than the atmosphere, with that sort of impetus given the right conditions there's no reason why gasses shouldn't accelerate past the speed of sound.
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Unread postAuthor: wannabie » Thu Jul 26, 2007 5:43 am

hmm i guess but then again i dont really get what you just said... so if i slightly understand what you just said and the gasses did reach the speed of sound isnt that what DDT is?
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Unread postAuthor: jackssmirkingrevenge » Thu Jul 26, 2007 6:27 am

DDT? Isn't that a pesticide :?

Gasses reaching the speed of sound will make a sonic crack, that's why explosions are so friggin loud ;)
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