How to make PVC Propeller Blade

PVC is:

The blades of an aeroplane propeller are rotating at the rate of 600 revolutions per minute. Its angular velocity is:

The blades of an aeroplane propeller are 2m long and rotate at the rate of 300rpm Calculate (i) the frequency (ii) the period of rotation (iii) the angular velocity (iv) the linear velocity of a point 0.5m from the tip of the blade .

Monomer of PVC is

Each propeller on a King Air twin-engine airplane consists of three blades. Each of mass 10 kg and length 125 cm . The blades may be treated approximately as uniform, thin rods. If the propeller is driven by an engine that develops a torque of 25 pi N m, how long (in sec). will it take to change the propeller's angular speed from 1400 rpm to 1640 rpm ?

How does the wind move the blades of a wind- mill ?

Why there two propellers in a helicopter ?