The wing chord may be varied along the span of the wing, for both structural and aerodynamic reasons. Constant chord: parallel leading & trailing edges. Simplest to make, and common where low cost is important, such as on the Piper J-3 Cub but inefficient as the outer section generates little lift while adding both weight and drag. Sometimes known in North America as the Hershey Bar wing due to its similarity in shape to a popular chocolate bar. Tapered: wing narrows towards the tip. Structurally and aerodynamically more efficient than a constant chord wing, and easier to make than the elliptical type. Trapezoidal: a tapered wing with straight leading and trailing edges: may be unswept or swept.Ilan Kroo. AA241 Aircraft Design: Synthesis and Analysis Wing Geometry Definitions, , Stanford University. The straight tapered wing is one of the most common wing planforms, as seen on the Messerschmitt Bf 109. Inverse or reverse tapered: wing is widest near the tip. Structurally inefficient, leading to high weight. Flown experimentally on the XF-91 Thunderceptor in an attempt to overcome the stall problems of swept wings. Compound tapered: taper reverses towards the root. Typically braced to maintain stiffness. Used on the Westland Lysander army cooperation aircraft to increase visibility for the crew. Constant chord with tapered outer section: common variant seen for example on many Cessna types. Elliptical: leading and trailing edges are curved such that the chord length varies elliptically with respect to span. Sometimes mistakenly said to be the most efficient (in aerodynamics theory, the term "elliptical" describes the optimal lift distribution over a wing of given span and not its shape), and also difficult to make. Famously used on the Supermarine Spitfire. Semi-elliptical: only the leading or trailing edge is elliptical with the other being straight, as with the elliptical trailing edges of the Seversky P-35. Bird wing: a curved shape appearing similar to a bird's outstretched wing. Popular during the pioneer years, and achieved some success on the Etrich Taube where its planform was inspired by the zanonia (Alsomitra macrocarpa) seed. Bat wing: a form with radial ribs. The 1901 Whitehead No. 21 has been the subject of claims to the first controlled powered flight. Circular: approximately circular planform. The Vought V-173 used large propellers near the tips, which helped to counteract its strong wingtip vortices, and had an outboard tail plane for stability. Flying saucer: circular flying wing. Inherently