psycix wrote:Surface of flow: 2*pi*r*r
There's no factor of 2 in area of a circle.
It's 2*pi*r for circumference, pi*r<sup>2</sup> for area - you have a blend of both. However, the ratio is fine.
The problem with dual valves is that the extra pipe work adds a lot of dead space.
I still have plans I drew up a while ago for a 30 bar four piston valve cannon with a 2 metre barrel (appropriately called Leviathan). GGDT tells me it would get 262m/s or 860 fps (2434 J/1795 ft-lbs) with a potato.
I was suffering from visions of kickass because the A-Team theme had come up on my music player though - I find that cannons change depending on the music I was listening to when I came up with them.
I'm almost tempted to try it, simply to see what that much power is like.