Rotor blade thrust - torque and angular velocity

1. Feb 22, 2016

ChromeBit

Imagine a motor, spinning a rotor blade around and around and around and around and around...

How does the angular velocity of the rotor blade, and the torque affect the thrust produced?

2. Feb 22, 2016

Staff: Mentor

Rotational speed is linearly related to airflow and airflow velocity, thrust is a square function of rotation rate.

Torque is also a square function of rotation rate because torque comes from aerodynamic drag.

3. Feb 23, 2016

CWatters

If this were a prop attached to a plane...

Angular velocity * Torque = Powerprop

That's the power required to turn the propeller. The power available to move the plane is somewhat less due to the efficiency of the prop..

Powerplane = Powerprop * Effprop

A well designed propeller might achieve 80% efficiency (with lots of caveats) but it will only achieve that under certain flight conditions.

The power required to move the plane (non accelerating flight) is roughly..

Powerplane = Thrust * Velocityplane

So with some substitutions...

Thrust = Angular velocity * Torque * Effprop/Velocityplane

The problem is not all are independent variables. For example prop efficiency will change with plane velocity.

PS: This equation is no use for testing a model plane prop on a bench (the plane velocity in that case would be zero, among other problems).