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# What infomation are needed to calculate fps for an air canon? Answered

I know that fps is speed unit, and I'm trying to calculate the initial speed(or the power) for my air canon. Information I have: 1: value of the air chamber 2: psi 3: diameter of the barrel 4: length of the barrel 5: diameter of the air release valve will those information be enough? How to calculate fps or power from information above?

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## 8 Replies

O.K What you need is GGDT It is a program used to calculate statistics of air guns, here is a link:
GGDT

DesChamos (author)2009-02-07

Well, if its not yet built and you're trying to predict it, the math is going to be complicated.
However, if it's already built and you simply want to know, I'd suggest making a ballistics pendulum. I couldn't find any instructables on it, so here's something I found with a quick google: Ballistic Pendulum.

Kiteman (author)2009-02-08

Also, page 147 of Backyard Ballistics by William Gurstelle.

Thelonelysandwitch (author)2009-02-07

you need a chronograph. To make the fps into mph, just divide fps by 1.47.

___ (author)2009-02-07

just a guess but you might need some statistics of the projectile?

benthekahn (author)2009-02-06

The only way to get an accurate calculation is to find the amount of feet the projectile travels in a certain amount of time. The formula is Feet traveled/Amount of time. As an example, if the projectile traveled 200 feet in 2 seconds, it would be traveling at 100 fps. (200/2)

ljfa321 (author)2009-02-06

I think he mean calculate by the pressure. Since he want to know the fps before actually building the things up.

benthekahn (author)2009-02-06

yeah, that would be hard to find though.