General Dynamics (GD) entered one of their designs in the Enhanced Tactical Fighter (ETF) competition to replace the F-111 but lost out to what became the McDonnell Douglas F-15E Strike Eagle. Of course the United States Air Force (USAF) still operates hundreds of F-15Es, and hundreds of GD F-16 Fighting Falcons (or Vipers) today. The design GD threw at the ETF competition is one of the most easily recognizable prototype aircraft ever built. Only two were created, initially using production F-16A numbers 3 and 5. Those airframes were transformed into the world’s only two F-16XLs.
But the F-16XL actually began as the F-16 Supersonic Cruise and Maneuver Prototype (SCAMP). Originally intended to show that supersonic transport (SST) aerodynamics had potential applications in military aircraft, the research took place over two years but was largely theoretical and model-based. It was found that a cranked-arrow wing shape would provide vastly increased lift without the usual limitations of a delta wing when paired with an F-16A fuselage. GD invested heavily in research and development and partnered with NASA to test more than 150 different configurations for 3600 hours in wind tunnels at NASA Langley.
The most distinctive feature of the F-16XL was its cranked-arrow delta wing. The wing was swept back at a lower angle (50 degrees) near the root (for supersonic performance) and at a higher angle (70 degrees) outboard (for subsonic stability and handling). The surface area of the wings, 633 square feet, was more than double the wing surface area of a standard F-16A, but drag was reduced. As one result, the aft-mounted ventral fins on standard F-16As were absent on the F-16XL.
GD and the USAF agreed to utilize the third full-scale development (FSD) F-16A airframe (A-3 serial 75-0747) and the fifth FSD airframe (A-5 serial 75-0749) for F-16XL conversion. Modifications included the cranked-arrow wings and addition of two fuselage sections, one forward and one aft totaling 56 inches. The wing skins were 600 pounds lighter thanks to carbon fiber construction, but the aircraft weighed almost 3,000 pound more than the standard F-16A. The wing contained fuel allowing both an 82 percent increase in internal fuel capacity and the ability to attach up to 27 stores stations.
The first F-16XL to fly was 75-0749. Powered by a Pratt & Whitney F100-PW-200 turbofan, she flew for the first time on July 3rd 1982. 75-0747, powered by a substantially more powerful General Electric F110-GE-100 turbofan, was badly damaged in a mishap before conversion. Rather than modify another airframe. 0747 received a new-build F-16B type two-seat forward fuselage at GD in Fort Worth. 0747 flew for the first time on October 29th 1982.
Fierce Competition with the Strike Eagle
Because of the F-16XL’s ability to carry twice the payload of a standard F-16 40 percent further and land or takeoff in two-thirds the distance used by the standard version, GD entered the aircraft in the USAF’s ETF competition. After a total of 798 F-16XL test flights, the long and the short of the result is today the USAF flies the Strike Eagle in the ETF role. The F-16XL was a more radical adaptation of the F-16 than the F-15E was of the F-15D, and the F-15 was already in production.
Though many believed (and some still do) that the F-16XL (or single seat F-16E and two-seat F-16F) would have been a better choice for the ETF, we’ll never know. The F-16XL failed to achieve supersonic cruise during the ETF competition.
In 1985 after the ETF competition concluded GD stored both F-16XLs at their plant in Fort Worth, Texas. The distinctive jets languished for three years before NASA made 0749 into their #849 and 0747 into their #848. NASA flew 849 to Ames-Dryden Flight Research Facility at Edwards Air Force Base (AFB) during March of 1989. 849 was modified for laminar-flow wing studies and also took part in sonic boom research. The aircraft has also spent time doing research flights at NASA’s Langley Research Center.
NASA and GD combined forces to replace the engine in 848. After receiving a production GE F110-129 engine, 848 eventually did achieve supersonic cruise (supercruise). 848 was modified with research gloves on both wings. The port wing glove was substantially larger. A team from NASA’s Langley Research and Dryden Research Centers, Rockwell International, Boeing, and McDonnell Douglas designed and built the wing glove. 848 was used primarily for supersonic laminar-flow research. Once NASA test programs concluded in 1999, both of these distinctive aircraft went into storage at Edwards AFB. They remain there today.