It's the abbreviation for the Sig Four Star 40 model. Pitch coupling ( there is also roll coupling, where the model wants to roll with rudder application) is the product of the relationships between the thrust line, center of gravity, wing and stab location, rudder area center, and dihedral when rudder is applied. Some pattern designs like the Eyeball and Banshee tried to eliminate it by putting thrust line, wing and stab location, and rudder area all on the same horizontal line. Nothing to these model airplanes, is there?>>>JIM