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small combustion cannon

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Unread postAuthor: pyromaniac » Thu May 31, 2007 10:39 pm

I can't find the pictures. or i am just stupid and you never posted them.
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Unread postAuthor: dyldo » Fri Jun 01, 2007 2:14 am

better one get an empty glue stick big or small drill a hole in the middle of the twisty thing at the bottom (this will also remove the central rod) you may also find the twisting bit will separate from the tube. a bit of glue will fix this :lol:
Image

get a little black sparker out of a reusable lighter hot glue, super glue or epoxy it in the hole let it cure


ready to fire remove the end cap spray in propellant as hi said wave it around put the cap on press the igniter in the base and the cap shoots off
great fun and pretty harmless if used properly
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put the gold end in the tube with the wire the black end is the clicker

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Unread postAuthor: jimmy101 » Fri Jun 01, 2007 12:15 pm

boilingleadbath wrote:"<i>The performance of a 10:1 cannon will suck</i>"

Not from a energy/barrel length perspective, which (for guns optimized for overall length) is is pretty close to the point.

My reasoning is that:
A) A mini is small, so the fast combustion approximation applies.
B) Under the fast combustion approximation, larger chambers mean less pressure drop over the cycle, which means higher average pressures.
C) Higher average pressure equals higher velocity.


So you think a pill bottle gun with a 10:1 ratio will outperform the same chamber with a longer barrel that gives ~1:1? (Or whatever the optimal CB is for a gun this small.)

The "small chamber fast combustion" makes sense, but a small chamber also goes with a short barrel which requires fast combustion. A mini typically has what, less than a 6" barrel. Compared to a "full size" gun that is 6 to 12 times shorter (compared to a 3' to 6' long barrel). To get the same muzzle velocity you would need the fuel to burn 6 to 10 times faster in the mini than in the full size gun. Or, you would need the mini to reach considerably higher chamber pressures.

Assuming constant acceleration:
Transit time for a 3' barrel at 300 FPS muzzle velocity is ~20mS
Transit time for a 6" barrel at 300 FPS muzzle velocity is ~3mS
Combustion has to be much faster in the mini than in the full size gun because there is a much shorter time frame to work with.

To put it another way, a mini has to burn faster in order to keep up with a large gun. There is no gross advantage to the faster burn rate in a mini versus a full size gun.
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Unread postAuthor: SpudBlaster15 » Fri Jun 01, 2007 3:18 pm

Well, considering the fact that in Latke's tests, a 373cc chamber was capable of burning the fuel quickly enough to produce 70psi over the course of a 2" long barrel, I think it is logical to reason that a similar effect will occur in a smaller pill bottle, which is coupled to a longer barrel.
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Unread postAuthor: fastcannonman » Fri Jun 01, 2007 3:49 pm

does it shoot far dyldo?
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Unread postAuthor: Will-91 » Fri Jun 01, 2007 8:19 pm

Thanks everyone, I was using way to much fuel. I works great. This is the first gun I ever made. Thanks again.
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Unread postAuthor: dyldo » Tue Jun 05, 2007 2:34 am

about 30-40 feet the cap is to light and not very aerodynamic i haven't realy tried modifying it though
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Unread postAuthor: TechnoMancer » Mon Jul 02, 2007 4:27 pm

i used to live in South Africa, we had axe there!!! now i live in New Zealand and they call the stuff Lynx here AFIK its the same stuff under a different name and by the ingredients it should burn exceptionally.

Ingredients: alcohol, butane and isobutane and propane, fragrance, isopropyl myristate, t-butyl alcohol

under that it says extremely flammable!!
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Unread postAuthor: MrCrowley » Mon Jul 02, 2007 4:36 pm

Hey another NZ'er! Welcome to the forums! Where in NZ are you?
Im in Auckland same with most other NZ'ers on the forum.
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