NOVELTY - The wing has two airfoil segments (30,32) having ends connected or fixed to one another at opposing neutral leading edge (20) and trailing edge (22). The segments are spaced apart from one another along their lengths across a neutral mean camber line (28) between both edges to form the neutral airfoil section (26) of the wing. The ability of each segment to resist compressive load causes the segment to adopt a form with a point of inflection, causing the wing to form a reflexed camber airfoil section.    USE - Wing for use as wing-sail, a rudder, a keel, or a hydrofoil for watercraft (all claimed). Can also be used as a main wing, horizontal tail stabilizer, vertical stabilizer, elevator or rudder for aircraft, a reciprocating blade or rotary blade on a propeller, rotor, and or fluid-driving or driven turbine, a wing-sail for a land-craft, or a wing for generating righting force to resist body roll or down-force for increased traction when used in a land-craft (all claimed).    ADVANTAGE - The wing may include a heavier trailing edge portion to keep the wing from rotating about an axis when the watercraft leans during roll. The trailing edge portion provides a self-righting function which reduces risk of watercraft from capsizing. The ability of the wing to deform into a reflexed camber airfoil section to either side of the neutral mean camber line provides the wing with full reversibility which provides forward propulsion or reverse propulsion or braking, providing the watercraft with increased control. Ability to vary the wing thickness not only reduces adverse yaw and tip stall, but also eliminate need for tail boom and rudder, resulting in improved fuel economy and reduced aircraft manufacturing cost. Utilizing the wing as a keel to provide the watercraft with active control eliminates need for heavy, cumbersome weight keels. Inclination at which the watercraft travels is controllable, virtually eliminating overturning.    DETAILED DESCRIPTION - The wing has two airfoil segments (30,32) having ends connected or fixed to one another at opposing neutral leading edge (20) and trailing edge (22) to keep the segments from sliding relative to one another. A skin (36) of fabric is supported over the segments. The segments are spaced apart from one another along their lengths across a neutral mean camber line (28) between both edges to form the neutral airfoil section (26) of the wing. The trailing edge is freely movable across the camber line. Actuators deform the wing between the neutral airfoil section and a reflexed camber airfoil section. The segments are also resilient to bias the wing towards an initial at rest airfoil section. Critical buckling of segments is greater than a compressive load generated between the segments by the actuator. When the wing is deformed by the actuator, displacement between two points on one segment generates the compressive load in the same segment. The ability of each segment to resist compressive load causes the segment to adopt a form with a point of inflection, causing the wing to form a reflexed camber airfoil section.    DESCRIPTION OF DRAWING(S) - The drawing shows the cross-sectional top view of a wing as wing-sail in initial at rest airfoil section form.    Opposing neutral leading edge (20)    Trailing edge (22)    Neutral airfoil section (26)    Neutral mean camber line (28)    Airfoil segments (30,32)    Skin (36)