Lift and drag force The intention of this option is, in a simplified way, to model the drag and lift forces for instance on a rudder as reponse to main propeller actions. The lifting surface is described by a local plane surface plane. The location is defined by a point P1 and the rotation axis, both defined in the body fixed coordinate system as illustrated in the figure. A surface coordinate system is defined, with the z axis along the rotation axis and the surface located in the xz plane. To avoid confusion, it is recommended to use a surface coordinate system with approximately the same orientation as the local body coordinate system.