Propeller P-factor

JSBSim has had the framework for modeling P-factor for some time now, but it's up to the modeler to provide the value (in inches per radian). This is the distance (in inches) that the propeller thrust vector is offset horizontally due to angle of attack (in radians). I've figured that a value of 0.79*D is a good approximation, where D is the propeller diameter in inches.

What this means in practice is that the Skyraider thrust vector will be offset about 2.5 inches to the right at 12 degrees of alpha (final approach alpha).