Four different versions of the General Dynamics F-16 shared the ramp at NASA’s Dryden Flight Research Center at Edwards, California, in this 1997 photo. At left and right are the only two F-16XL prototypes built. The two-seat version to the left, NASA registration number 848, was flown in a supersonic laminar flow control experiment until late 1996. The single-seat F-16XL at right, NASA registration number 849, was flown in a variety of experiments, including an earlier laminar-flown study and sonic boom attenuation research. At center left is a single-seat F-16A, NASA registration number 816, the only civil registered F-16 in existence. Although it is flight-worthy, it is not currently flown at Dryden and is carried in ''flyable storage.'' At center right is the U.S. Air Force Advanced Fighter Technology Integration (AFTI) F-16A. NASA Dryden provided hangar space and maintenance services for this Air Force program which evaluated a variety of new sensors and control systems to enhance the combat capability of future tactical aircraft.