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.[28][29] 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.[30][31] The Sukhoi Su-47 Berkut is another notable demonstrator aircraft implementing this technology to achieve high levels of agility.[32] To date, no highly swept-forward design has entered production.