# Calculating thrust from CFM?

I'm trying to calculate thrust of a fan for a hovercraft project thing. Basically, I have some computer fans that have:
1) a radius of 60mm (120mm fan)
2) a CFM of 252.
Basically, I was using this formula:
CFM = Cubic Feet per Minute = Volumetric Flow Rate
Mass Flow Rate = (Density) x (Volumetric...
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I'm trying to calculate thrust of a fan for a hovercraft project thing. Basically, I have some computer fans that have:

1) a radius of 60mm (120mm fan)

2) a CFM of 252.

Basically, I was using this formula:

CFM = Cubic Feet per Minute = Volumetric Flow Rate

Mass Flow Rate = (Density) x (Volumetric Flow Rate)

Newton’s Second Law of Motion: Force = (Mass) x (Acceleration), or F = ma

F = ma = (Mass Flow Rate) x (Velocity), given a constant flow velocity

(i.e., constant propeller speed and pitch angle).

Velocity = (Volumetric Flow Rate) / (Area), where Area = (Pi) x (r^2), the

length of a propeller blade is a good approximation for the radius, r.

Thrust = (Density) x (CFM^2) / ((Pi) x (r^2))

I was alright until they brought density into it. I take it they mean the density of the air?

Anyways, could someone tell me how much weight that fan could lift, and how they got there?

Thanks!

1) a radius of 60mm (120mm fan)

2) a CFM of 252.

Basically, I was using this formula:

CFM = Cubic Feet per Minute = Volumetric Flow Rate

Mass Flow Rate = (Density) x (Volumetric Flow Rate)

Newton’s Second Law of Motion: Force = (Mass) x (Acceleration), or F = ma

F = ma = (Mass Flow Rate) x (Velocity), given a constant flow velocity

(i.e., constant propeller speed and pitch angle).

Velocity = (Volumetric Flow Rate) / (Area), where Area = (Pi) x (r^2), the

length of a propeller blade is a good approximation for the radius, r.

Thrust = (Density) x (CFM^2) / ((Pi) x (r^2))

I was alright until they brought density into it. I take it they mean the density of the air?

Anyways, could someone tell me how much weight that fan could lift, and how they got there?

Thanks!

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