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question about difference in sound

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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question about difference in sound

Unread postAuthor: mindtrickonu » Mon Dec 11, 2006 2:31 pm

when i built my first cannon i was able to spray in a bit of starter fluid and i took a hose from a compressed air tank and sprayed about 2 secs. of air and when i fired it (without a projectile) it would make this really low pitched low bass bang that rattled the windows of my house...now after i installed a fan inside ... i would spray the starter fluid in ... turn the fan on for about 5 secs. and when fired it would shhot out some flame but not a very loud sound ... whats the deal??
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Unread postAuthor: Tshylea » Tue Dec 12, 2006 8:30 am

If it shoots flame out I would assume your barrel is too short. I'm not sure about the sound though because a shorter barrel should make it louder. How big is your chamber and how long is the barrel?
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Unread postAuthor: joannaardway » Tue Dec 12, 2006 10:24 am

If it's shooting flames, you're using way too much fuel, and the uncombusted starter fluid is igniting as it comes into contact with air.

Try less fuel, and you should get better results and no flames from the muzzle.
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Unread postAuthor: mindtrickonu » Tue Dec 12, 2006 11:30 am

well my chamber is 3 ft long 4 inch pipe reduced down to a 1ft section of 3 inch pipe reduced down to a 5 ft long 2 inch barrel ... and im not using that much starter fluid ... i spray about .3 seconds and i fire it and i get that kind of sound
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Unread postAuthor: joannaardway » Thu Dec 14, 2006 4:38 am

In that case, your barrel's too short. You could support a 14-15 ft barrel on that chamber size.

Are you still doing it without a projectile? In that case, your fan might well be shifting your starter fluid up the barrel.
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Unread postAuthor: mindtrickonu » Thu Dec 14, 2006 1:55 pm

really?? a 15 foot barrel ??? .... am i underbarreling that much??
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Unread postAuthor: HAYLO_Stealer » Thu Dec 14, 2006 4:09 pm

he said hes not using a projectile
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Unread postAuthor: frankrede » Thu Dec 14, 2006 4:22 pm

3 foot chamber for a combustion?
That sounds really bad witht that short of a barrel.
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Unread postAuthor: joannaardway » Fri Dec 15, 2006 5:00 am

Yes, really...

A 3' section of 4": 452 ci
A 1' secton of 3": 85 ci

Total chamber volume: 537 ci

Each foot of 2" pipe is about 37.7 ci

For a 1:1 chamber ratio: 537/37.7 = 14' 3" of barrel.

Assuming even a 1.5:1 ratio, then you could have around 10' of barrel.
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Unread postAuthor: mindtrickonu » Sat Dec 16, 2006 2:14 am

(now ya made me feel dumb ) :? wow .... thats interesting .... well lol i just added a 1 ft section to the chamber, so the barrel needs to be aruond 20 ft?? .... i want it to be portable ... i guess theres a way i could make it to where the barrel is a few pieces of PVC ... hmm ... to the drawing board!
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