Originally posted by uzless
You have a propellor attached to a shaft which is attached to an engine. You are a smart guy and realize that the centre of the propellor will be rotating at a slower speed than the outside edges of the propellor
So, when calculating the minimum amount of power needed to turn the propellor 1 revolution/second, do you calculate how much power is required t ...[text shortened]... or do you calculate how much power is required to turn the outside of the propellor at speed y?
You can sidestep the whole issue by calculating power as the product of torque and rotational speed:
power = (2*pi) * torque * rotational speed
In fact, I think it only makes sense to do it this way. The speed of the innermost part of the propeller and the outermost part of the propeller are related by the ratio v(inner)/v(outer)= 2*pi*r(inner) / 2*pi*r(outer) = r(inner)/r(outer), so you only need to define one variable (the rotational speed) in order to delineate the speed of any particular position on the propeller.