The General Dynamics F-16XL is a derivative of the F-16 Fighting Falcon with a cranked-arrow delta wing. It entered the United States Air Force's (USAF) Enhanced Tactical Fighter (ETF) competition in 1981 but lost to the F-15E Strike Eagle. The two prototypes were shelved until being turned over to NASA for additional aeronautical research in 1988. Both aircraft were fully retired in 2009 and stored at Edwards Air Force Base.
Development
SCAMP
Shortly after winning the lightweight fighter program, General Dynamics Fort Worth began investigating possible derivatives with the goal of enhancing both air-to-air and air-to-ground mission capabilities while retaining parts commonality with the . Under the leadership of Harry Hillaker (designer of the original ), the Supersonic Cruise and Maneuver Prototype (SCAMP) project was started. Several wing designs were considered, including one using a forward-swept wing, but the large "cranked-arrow" wing (similar to that of the Saab 35 Draken) was pursued due to its much more efficient lift-to-drag ratio at supersonic speeds.
The company worked closely with NASA's Langley Research Center and invested significant R&D funds for wind tunnel testing. Over several years the design was refined which led to the final design by late 1980.
Enhanced Tactical Fighter competition
In 1980, the USAF signed on as a partner, providing the fuselages of the third and fifth production s for conversion. These two fuselages became the only examples of the .
In March 1981, the USAF announced the Enhanced Tactical Fighter (ETF) program to procure a replacement for the F-111 Aardvark. The concept envisioned an aircraft capable of launching deep interdiction missions without requiring additional support in the form of fighter escorts or jamming support. General Dynamics submitted the while McDonnell Douglas submitted a variant of the F-15 Eagle. Though the two aircraft were competing for the same role, they had fairly different design approaches. The required very few alterations from its base , while the had major structural and aerodynamic differences from the original . As such, the would have required much more effort, time, and money to put into full production. Additionally, the had two engines, which gave it a much higher maximum takeoff weight and redundancy in the case of engine failure.
In February 1984, the USAF awarded the ETF contract to McDonnell Douglas. The two were returned to the Air Force and placed in storage at Edwards Air Force Base. Had General Dynamics won the competition, the would have gone into production as the F-16E/F (E for single seat, F for two seats).
Design
The wing and rear horizontal control surfaces of the base were replaced with a cranked-arrow delta wing 115% larger than the original wing. Extensive use of graphite-bismaleimide composites allowed the savings of of weight, but the and were and heavier respectively than the original .
Less noticeable is that the fuselage was lengthened by by the addition of two sections at the joints of the main fuselage sub-assemblies. With the new wing design, the tail section had to be canted up 3.16°, and the ventral fins removed, to prevent them from striking the pavement during takeoff and landing. The also received a larger inlet which would go on to be included in later variants.
These changes resulted in a 25% improvement in lift-to-drag ratio in supersonic flight while remaining comparable in subsonic flight, and a plane that reportedly handled smoothly at high speeds and low altitudes. The enlargements increased internal fuel capacity by , or about 65%. The could carry twice the ordnance of the and deliver it 50% farther. The enlarged wing and strengthened hardpoints allowed for a highly configurable payload: