Wind shear.  A sudden, drastic shift in wind speed, direction,  or both that may occur in the horizontal or vertical plane. Wing.  A fabric skin with an aluminum frame that produces  the lift necessary to support the WSC in flight; including the  flight wires/control frame below and the ground wires/king  post above.  Wing keel.  The WSC structural component in the longitudinal  center of the wing that connects the two leading edges  together at the nose and connects the carriage to the wing. Wing loading.  The amount of weight that a wing must  support to provide lift. Wingspan.  The maximum distance from wingtip to  wingtip. Wing twist.  A design feature of the WSC that reduces the  angle of attack from the root to the tip. Wingtip vortices.  The rapidly rotating air that spills over an  aircraft’s wings during flight. The intensity of the turbulence  depends on the aircraft’s weight, speed, and configuration. It  is also referred to as wake turbulence. Vortices from heavy  aircraft may be extremely hazardous to small aircraft. World Aeronautical Charts (WAC).  A standard series  of aeronautical charts covering land areas of the world at a  size and scale convenient for navigation (1:1,000,000) by  moderate speed aircraft. Topographic information includes  cities and towns, principal roads, railroads, distinctive  landmarks, drainage, and relief. Aeronautical information  includes visual and radio aids to navigation, airports, airways,  restricted areas, obstructions and other pertinent data. WSC.  See weight-shift control. Weight-Shift Control—Land (WSCL).  WSC that takes off  and lands on land. This can be wheels or ski equipped. Weight-Shift Control—Sea (WSCS).  WSC that takes of the  water. This can be pontoons or a boat configuration. Yaw.  Rotation about the vertical axis of an aircraft. Zulu time.  A term used in aviation for Coordinated Universal  Time (UTC) which places the entire world on one time  standard.  G-20