Researchers flew the X-29 to explore advanced composite materials in aircraft construction, variable-camber wing surfaces, forward-swept wings with a thin supercritical airfoil, close-coupled canards, and digital fly-by-wire controls. The digital fly-by-wire system made the inherently unstable aircraft flyable, while the complex wing and canard geometries provided exceptional maneuverability. Air moving over the forward-swept wings tended to flow inward toward the wing root rather than outward toward the wingtip, preventing the wingtips and their ailerons from stalling before the rest of the wing and giving pilots greater control. To reduce cost, the X-29 was assembled from as many off-the-shelf aircraft components as possible, including landing gear from an F-16, a cockpit from an F-5, and the same type of engine used on the F-18. Its wings and canards were constructed entirely from carbon fiber composites, the first such aircraft structures ever built. Two X-29 aircraft were flown 422 times between 1984 and 1992.