Stock Photo - Four different versions of the F_16 were used by Dryden in the 1990s. On the left and right sides are two F_16XLs. On the left is the F_16XL 2 NASA 848, which is the two_seat version, used for advanced laminar flow studies until late 1996. On the right is the single_seat F_16XL 1 NASA 849, used for laminar flow research and sonic boom research. Laminar flow refers to smooth airflow over a wing, which increases lift and reduces drag compared to turbulent airflow. Between them at center left is an F_16A NASA 816, the only civilian operated F_16. Next to it at center right is the U.S. Air Force Advance Fighter Technology Integration AFTI F_16, a program to test new sensor and control technologies for future fighter aircraft. Both F_16XLs and the F_16A are in storage at Dryden. The AFTI F_16 is in the Air Force Museum.