An elliptical wing is a wing planform whose leading and trailing edges each approximate two segments of an ellipse. It is not to be confused with annular wings, which may be elliptically shaped. Relatively few aircraft have adopted the elliptical wing, an even-smaller number of which attained mass production; the majority of aircraft that did use this feature were introduced during the 1930s and 1940s. Perhaps the most famous aircraft to feature an elliptical wing is the Supermarine Spitfire, a Second World War-era British fighter aircraft. Another major application was the Heinkel He 70 "Blitz", a German fast mail plane and reconnaissance bomber; early versions of the He 111 bomber also used such a wing configuration before a simpler design was adopted for economic reasons. Properties Theoretically, the most efficient way to create lift is to generate it in an elliptical spanwise distribution across the wing. There is no inherent superiority to pure elliptical shapes, and wings with other planforms can be optimized to give elliptical spanwise lift distributions. The basic elliptical wing shape also has disadvantages: The almost uniform lift distribution of a constant-aerofoil section elliptical wing can cause the entire span of the wing to stall simultaneously, potentially causing loss of control with little warning. To improve the stalling characteristics and give the pilot some warning, designers use a non-uniform aerofoil. For example, the wing of the Supermarine Spitfire was both thinned towards the tips and twisted to give washout, reducing the load on the tips so that the inner wing would stall first. Such compromises depart from the theoretical elliptical lift distribution, increasing induced drag. An elliptical spanwise lift distribution cannot be achieved by an untwisted wing with an elliptical planform because there is a logarithmic term in the lift distribution that becomes important near the wing tips. Elliptical wing planforms are more difficult to manufacture. In it, either leading edge or trailing edge or both are curved, and the ribs change in a non uniform way along the wingspan. In practice, most elliptical wings are approximations, for example several sections of the Spitfire leading and trailing edges are arcs of circles. The semi-elliptical wing For a wing to have an elliptical area distribution, it is not necessary for both the leading and trailing edges to be curved. If one of these is straight, as in the semi-elliptical planform, the wing may still have an elliptical area