The Hornet's normally high angle-of-attack performance envelope was put to rigorous testing and enhanced in the NASA F-18 High Alpha Research Vehicle (HARV). NASA used the F-18 HARV to demonstrate flight handling characteristics at high angle-of-attack (alpha) of 65-70 degrees using thrust vectoring vanes. F/A-18 stabilators were also used as canards on NASA's F-15S/MTD. The F/A-18 is a twin engine, mid-wing, multi-mission tactical aircraft. It is superbly maneuverable, owing to its good thrust to weight ratio, digital fly-by-wire control system, and leading edge extensions (LEX). The LEX allow the Hornet to remain controllable at high angles of attack. This is because the LEX produce powerful vortices over the wings, creating turbulent airflow over the wings and thus delaying or eliminating the aerodynamic separation responsible for stall, allowing the Hornet's wings to generate lift several times the aircraft's weight, despite high angles of attack. The Hornet is therefore capable of extremely tight turns over a large range of speeds.