CG CG Side View Flightpath Wing Root Tip Chord Wing Root Rear View Leading Edge Wing Span Wing Tip Wing Root Tip Chord Anhedral Angle (Dihedral would be the  wing angled up) Trailing Edge Figure 2-4.  Side view of a WSC wing and aerodynamic terms. Figure 2-5.  Rear view of a WSC wing and aerodynamic terms. Looking at the rear view of the wing, anhedral is the angle  the wings make angling down and dihedral is the angle the  wings make angling up.  [Figure 2-5]  Dihedral is the positive  angle formed between the lateral axis of an airplane and a line  which passes through the center of the wing. Anhedral is the  similar negative angle. Wings with sweep have an “effective  dihedral” characteristic that counteracts the physical anhedral  to develop the required roll stability for the particular make/ model design objective. This is explained in the Pilot’s  Handbook of Aeronautical Knowledge in much greater detail  for further reference. Unlike airplanes which typically have  significant dihedral as viewed from the front or back for  roll stability, WSC wings typically have a slight amount of  anhedral as shown in  Figure 2-5  and effective dihedral which  is a characteristic of the swept wing design.  Wing twist is the decrease in chord angle from the root  to the tip chord, common to all WSC wings and ranging  from 5° to 15°. This wing twist is also called washout as  the wing decreases its angle of attack from root to tip. The  term billow was originally used for the early Rogallo wings  as the additional material in degrees that was added to the  airframe to create the airfoil. It is still used today to defi ne the  amount of twist or washout in the wing. The WSC may not  have twist/washout when sitting on the ground, and must be  flying and developing lift to display the proper aerodynamic  twist characteristic of WSC wings.  [Figure 2-6] The longitudinal axis is an imaginary line about which the  aircraft rolls around its center of gravity (CG); it is also  called the roll axis. The longitudinal axis is not necessarily a  fixed line through the carriage because the roll axis changes  for different fl ight configurations, but can be approximated  by the middle of the propeller shaft for a properly designed  WSC aircraft and is typically parallel with the fl ightpath of  the aircraft as shown in  Figure 2-7.  Angle of incidence is  the angle formed by the root chord line of the wing and the  longitudinal axis of the WSC aircraft. 2-3