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design question

A place to ask general spud cannon related questions.
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design question

Unread postAuthor: Moonbogg » Fri Dec 19, 2008 6:12 pm

Do you lose a lot of power when going from, say, a 4" chamber to a 2" U-bend, and then lets say you step down to 1.5" and then your barrel is 2". Does that smaller 1.5" diameter section between your chamber and your barrel constrict or bottleneck the airflow? I was thinking it shouldn't be THAT big of a deal since pneumatics have tiny passageways through the valves. I am making a combustion cannon but this is for my general knowledge as well. Hope iamb being sort of clear at least.
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Unread postAuthor: Hotwired » Fri Dec 19, 2008 6:34 pm

Pneumatic rifles and pistols are in another league both in requirements and engineering capability.

They use co2 or several thousand psi HPA, comparatively small projectiles, they also have a requirement for efficient use of the gas in the reservoir.

If they used a full barrel bore port from the chamber then spectacular energies could result but at a significant use of gas and loss of pressure. Instead they allow a small volume of high pressure gas to escape per shot which is sufficient for the barrel length and pellets used. All cannons in here have huge muzzle blast from the massive load of gas used per shot, that is inefficient.

However since most cannons in here are single shots from single charges of gas there is no requirement to restrict flow and therefore energy.

In a combustion there certainly isn't a reason to have a bottleneck, the better the flow from chamber to barrel the faster energy can be transmitted during the deflagration. The pressure can't be easily stored and lasts for a very short period of time after all.
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Unread postAuthor: jimmy101 » Sat Dec 20, 2008 7:25 pm

In a combustion, flow restrictions are rarely important as restrictions. What is much more likely to be important is increased heat loss through all that plumbing. In particular, a narrow pipe between the chamber and barrel is goig to act as a huge heat sink.
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