Variants of the delta wing plan offer improvements to the basic configuration. Most supersonic jets use a swept or delta wing. The design was later abandoned in favor of a more conventional tailed delta wing. The Saab 35 Draken is a fighter aircraft, equipped with a distinctive double delta wing. The optimum solution was thought to be a double delta wing. The delta wing form has unique aerodynamic characteristics and structural advantages. The Shuttle's delta wing design was driven by these issues. However on a delta wing the leading edge sweep defines the wing sweep. The X-32 therefore was designed around a large one piece carbon fiber composite delta wing. The two X-32 aircraft featured a delta wing design. Features included a delta wing and a drooped nose. A competing contract was also awarded for the delta wing Douglas F4D Skyray. In 1963 Lippisch developed the X-112, a revolutionary design with reversed delta wing and T-tail. Production Tu-144s replaced this wing with a double delta wing including spanwise and chordwise camber. Air-breathing hypersonic first stage and delta wing second stage.