You did account for weight, right?
One of the possible reasons is that you have to take into account that when a propeller is moving, it's thrust will be reduced. The second thing you have to take into account is that the air within the propeller starts to rotate around, effectively reducing airspeed over the propeller airfoil.
One of the possible reasons is that you have to take into account that when a propeller is moving, it's thrust will be reduced. The second thing you have to take into account is that the air within the propeller starts to rotate around, effectively reducing airspeed over the propeller airfoil.