pushing the aircraft further into stall similar to a swept back wing design. Thus swept-forward wings are unstable in a fashion similar to the low-speed problems of a conventional swept wing. However unlike swept back wings, the tips on a forward swept design will stall last, maintaining roll control. Forward-swept wings can also experience dangerous flexing effects compared to aft-swept wings that can negate the tip stall advantage if the wing is not sufficiently stiff. In aft-swept designs, when the airplane maneuvers at high load factor the wing loading and geometry twists the wing in such a way as to create washout (tip twists leading edge down). This reduces the angle of attack at the tip, thus reducing the bending moment on the wing, as well as somewhat reducing the chance of tip stall. However, the same effect on forward-swept wings produces a wash-in effect that increases the angle of attack promoting tip stall. Small amounts of sweep do not cause serious problems, and had been used on a variety of aircraft to move the spar into a convenient location, as on the Junkers Ju 287 or HFB 320 Hansa Jet. However, larger sweep suitable for high-speed aircraft, like fighters, was generally impossible until the introduction of fly by wire systems that could react quickly enough to damp out these instabilities. The Grumman X-29 was an experimental technology demonstration project designed to test the forward swept wing for enhanced maneuverability during the 1980s. The Sukhoi Su-47 Berkut is another notable demonstrator aircraft implementing this technology to achieve high levels of agility. To date, no highly swept-forward design has entered production. History Early history The first successful aeroplanes adhered to the basic design of rectangular wings at right angles to the body of the machine, but there were experimentalists who explored other geometries to achieve better aerodynamic results. The swept wing geometry appeared before World War I, and was conceived as a means of permitting the design of safe and stable aeroplanes. The best of these designs imposed "self-damping" inherent stability upon a tailless swept wing. These inspired several flying wing gliders and some powered aircraft during the interwar years. The first to achieve stability was British designer J. W. Dunne who was obsessed with achieving inherent stability in flight. He successfully employed swept wings in his tailless aircraft (which, crucially, used washout) as a means of creating positive longitudinal static