when looking at a cross-section. A wing possesses upper  camber on its top surface and lower camber on its bottom  surface. WSC airfoils can be single surface, with one piece of  fabric for most of the airfoil, for slower wings. Faster airfoils  have two surfaces and are called double surface wings, which  are more like an airplane wing.  [Figure 2-1]  This double  surface allows the wing structure to be enclosed inside the  wing, similar to an airplane wing, reducing drag and allowing  for faster speeds for the same thrust. The leading edge is the  forward edge of the airfoil, and the rear edge of the airfoil  is called the trailing edge. The chord line is an imaginary  straight line drawn from the leading edge to the trailing edge.  The WSC airfoil typically uses a different camber with the  airfoil high point farther forward than the airplane airfoil,  creating a more stable airfoil.  [Figure 2-2] The WSC wing is a unique design of airfoils that differ  throughout the wing span. Looking at a top view of the wing,  in the center is the wing root and on each end is the wingtip.   Wing chord is any section of the wing parallel to the wing  root.  [Figures 2-3  and  2-4]  The wingtip chord is the chord  where the trailing edge is furthest to the rear of the wing. This  can be inboard of the tip (as shown) and can vary depending  on the specific wing design. The nose angle is the angle made  by the leading edges, typically ranging from 120° to 130°.  Sweep is the angle measured between the quarter chord line  (line of 25 percent chords) and a line perpendicular to the  root chord.  [Figure 2-3] Chord Line U p e r  $_{C}$ a$_{m}$ b e r Lower Ca mber Chord Line U p e r C a m b e r L o w e r C a m b e r Relative Wind Flightpath Single Surface Wing Double Surface Wing Trailing Edge Leading Edge CG Top View Leading Edge Trailing Edge Sweep Angle Flightpath Wing Tip Wing Root Chord Tip Chord Nose Angle Wing Chords Quarter Chord Chord Line T y p i c a l A i r p l a n e A i r f o i l Airplane Airfoil WSC Airfoil Airfoil Shape of WSC Compared to Airplane WSC High Point Farther forward  for stable airfoil Airplane High Point WSC Airfoil Figure 2-2. Airplane airfoil compared to WSC airfoil. Figure 2-1. WSC airfoil terms showing a single surface and a  double surface wing. Figure 2-3.  Top view of a WSC wing and aerodynamic terms. 2-2