Paul,

 

Good concept, but I think you have made it more complicated than it needs to be. Rather than calculating a moment arm from the prop center to the wheel and then correcting the scale force to this moment arm, you could simply use the moment arm between the scales and the direct scale readings.

 

Thus: T = (dR + dL) * d/2  where "T" is in lb ft, "dR" and "dL" are in lb and "d" is in ft.

 

HP is then simply T * rpm / 5252.

 

The answer should be the same either way.

 

Rob