More distance

[Mattmp36]

Hows it goin? I'm new to the potato cannon world and I love it! I wanted some more distance with my gun. I was able to fire a potato 540 feet. I saw a kid fire one 740 feet. How can I get more distance? I have a PVC cannon: 4"diameter combustion chamber, 18"long and a 2"diameter barrel, 44"long. I have to wear ear plugs when using it! At night, it shoots out a foot of fire! I love that thing! I want more distance with my potato though. Should I make it a 1.5" barrel instead of the 2"? What could do? Thanks.

[lukemc]

add a computer fan in the chamber it significantly increases performance because it mixes the fuel. also if you have the suppplys / money build a propane meter and that will also significantly increase your distance

[SpudBlaster15]

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[Kenny_McCormic]

what fuel are you using?
if yopur cannon is all pressure rated then try some starting fluid

[Mattmp36]

That sounds cool, except the 10 foot barrel. I would like to keep the barrel the same length as the one I have now, just a smaller diameter, so how small would I need to make the combustion chamber?

Merged:

what fuel are you using?
if yopur cannon is all pressure rated then try some starting fluid

I'm using Oust Airsanitizer. I know it sounds funny, but that is the only thing so far I have found to work very well.

[SpudBlaster15]

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[Modderxtrordanare]

If I did my math correctly, then your gun as it stands has a 1.6:1 C:B ratio.

If you cut your chamber down to 12" that should increase your preformance. Also, as it's been suggested, try building a metered propane system, that'll help you alot.

(I don't know if I did my C:B ratios right, since I'm more of a pneumatic person)

[rednecktatertosser]

I believe the ideal C:B ratio is around .7:1 so if you shorten your chamber to 7 or 8 inches you should be right on the money and you should see a boost in perfomance

and modder, yes your calculations were correct he is currently at a 1.6:1 ratio, which is huge.

also if you shorten your chamber you should notice that it wont be as noisy.

[SpudBlaster15]

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[rednecktatertosser]

I thougt that if he changed it to the 'ideal' C:B ratio it would increse performance.

[SpudBlaster15]

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[rednecktatertosser]

Ok, well I was passing along info I have read here and on spudtech, I assumed it was correct and havent really done anything with combustions personally, so i dont really know for sure.

[jimmy101]

That is only the case is the chamber is oversize by a considerable degree. Research has not been done to establish the exact ratio at which this occurs in a conventional cannon.

Spudbalster's second sentence is correct, nobody has ever measured (TIKO) variable chamber on a constant barrel.

My combustion model suggests that C:B ratios in the range of 0.6 to about 1 are all essentially equivalent on a constant barrel. (Similar to Latke's results with constant chamber; relatively little difference in the range of about 0.6 to 1.0.) "Essentially equivalent" means the muzzle velocity changes by less than ~5% over that CB range.

At a C:B of 1.5:1 the muzzle velocity drops by ~10%.
At a C:B of 3.0:1 the muzzle velocity drops by ~30%.

So, by my model, on my standard gun, up to a ratio of about 1.5 there is minimal difference (though 1.0 is better than 1.5). Above 1.5 the performance starts to drop off pretty quickly.
<hr>
Back to Mattmp36 post. A chamber fan is probably the easiest way to get the maximum performance out of a particular combustion gun.

A fuel meter would be second most important. (A syringe is a cheap way to measure fuel, less than $2 total cost, and is at least as accurate as a much more expensive meter setup.)

The actual fuel makes relatively little difference as long as you are using the correct amount and are mixing it well.

A double bevel spud cutter might give you a little more range.

[boilingleadbath]

Your chamber is what many would consider oversize, and the flame emerging from your barrel suggests:
1) an overly rich fuel mix (get a metering system)
2) incomplete combustion (get chamber fan and/or multiple ignition points)

#2 will help alot; latke noted much benefit from a chamber fan, and multiple ignition points will almost certainly help (especially with an oversized chamber).
***********

As a quip for contention:

"there are no oversized chambers - only poor ignitions."
Even with the slow combustion model.

[roughboy]

Or build a pneumatic cannon coz it's more more powerful and not as loud as a combustion.