[3] As understanding of thermal soaring grew in the 1930s, glider pilots and designers became aware of two conflicting requirements for cross country flights.
A solution to this problem was to extend the whole trailing edge, including the ailerons, and this route was taken by both the disappointing, heavy and complicated Operation Sigma Sigma, the more successful but still heavy and complex Akaflieg München Mü27 and the World Championship winning 15 m class Akaflieg Braunschweig SB-11.
As it is extended, a track in the fuselage side guides the thin flap into its high camber position at the wing root.
When the flaps, pivoted immediately inboard of the ailerons, are deployed the wing trailing edge becomes almost straight, making the plan almost triangular, and 12° of washout is generated by the now strongly cambered inner sections.
This produces a lift distribution close to that of the ideal elliptical wing, with its minimum induced drag.
The rather wide cockpit occupies most of the deeper forward fuselage and has a long, one piece, front hinged canopy.
The more experienced Helmut Reichmann did show, at one competition, that the D-40 outperformed the other sailplanes present under weak thermal conditions, as hoped for.