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Experience with C:B Ratio

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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Unread postAuthor: Ragnarok » Wed Dec 10, 2008 8:46 pm

Xxplosive42o wrote:Rag, that was... interesting. lol

We do that here. Random off-topic.

In a refutation, I said I am looking for what’s best. By best I mean which barrel "will shoot the darn potato the furthest" to be frank.

And how are we supposed to know that's what your definition of best is?
Because, it certainly isn't my definition of best - not many people here have the same idea of best, that's why so many different styles of cannon exist. And after a while, most people who were originally after range start looking into other avenues. Few experienced spudders put "Range" high up their list of things they feel are important in a cannon - their cannons might well be capable of huge ranges, but they're not bothered about it.

And for many people, best may well include considerations for sound levels or portability.

I understand the graph Jack posted was muzzle velocity, so wouldn’t that show approx. how far the projectile will travel given the trajectory was controlled?

Don't delude yourself into believing spuds have a controllable trajectory. They have about the same level of control as a monkey on crack with a conspiracy theory and the will to impose those ideas on other people with violence.

Also, that test was done with a 1.5" barrel; will a 2.0" differ?

Not by any great amount, at least in terms of volume ratios.

I stated I will be using a chamber with a volume of 236.5" and a barrel of 2" with an unknown length. I just want the best "performance" per say, while not giving a darn about cost of propane.

If range is your only concern, I would recommend a 0.7:1 C:B ratio. Gives essentially the same power as 0.8:1, but slightly quieter, and will produce less muzzle blast, thus a slightly less erratic first trajectory section.

For a 2" SCH 40 barrel, and assuming your chamber volume correct, that would be a barrel of 100 inches in length.
Slightly less than practical, you may well agree - hope you're not planning on taking it anywhere.
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Does that thing kinda look like a big cat to you?
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Unread postAuthor: Xxplosive42o » Wed Dec 10, 2008 9:07 pm

Haha well thank you Rag. I now understand your logic. The only reason distance is a concern is because my first cannon was an embarrassment. It MAYBE fired a projectile 200 yards. That was about 3 years ago on my first build which was completely uneducated. This is my first endeavor into the field of metered propane injection so forgive me if my questions may sound "empty". I wouldn't mind a loud and powerful kick, so I may just wind up building a couple barrels with a cam-lock setup to see what suites me best. The 100 inch length is WAY impractical. So I might have to build with a 1:1 ratio barrel at 72" and a 1.5:1 ratio at 48" for some close up destruction.
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Unread postAuthor: Ragnarok » Wed Dec 10, 2008 9:22 pm

Xxplosive42o wrote:The only reason distance is a concern is because my first cannon was an embarrassment. It MAYBE fired a projectile 200 yards.

Assuming that to be an accurate range, and not the usual overestimate many newbies proclaim (As a general rule, most newcomers overestimate their cannons by a factor of at least 2), that's far from an embarrassment.

A really good and meatily-sized combustion might be able to push a spud a little over 300 yards, but more than that is definitely unlikely.

200 yards, if that is a reliable figure, is very decent for a first cannon.
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Unread postAuthor: Xxplosive42o » Wed Dec 10, 2008 10:29 pm

I measured it using one of those rolling measuring units. The pieces of the potato recognizable lay roughly 190 yards from launch point. I used an excel program to find its C:B and it was .9 using a 1.5" barrel. Although, it was built rather primitive without any fan, spark strip, nor did it have a propane injection system. Not bad for a first build almost 3 years ago I suppose. The entire thing was done without any calculations nor measurements. This new cannon will improve on every aspect of that one.
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