The NASA Dryden Flight Research Center, Edwards, California, used an F-18 Hornet fighter aircraft as its High Angle-of-Attack (alpha) Research Vehicle (HARV) in a three-phased flight research program lasting from April 1987 until September 1996. The aircraft completed 385 research flights and demonstrated stabilized flight at angles of attack between 65 and 70 degrees using thrust vectoring vanes, a research flight control system, and (eventually) forebody strakes (hinged structures on the forward side of the fuselage to provide control by interacting with vortices that are generated at high angles of attack, and thus create side forces).

This combination of technologies provided carefree handling of a fighter aircraft in a part of the flight regime that was otherwise very dangerous. Flight research with the HARV increased our understanding of flight at high angles of attack, enabling designers of U.S. fighter aircraft to design airplanes that will fly safely in portions of the flight envelope that pilots previously had to avoid.

Angle of attack (alpha) is an aeronautical term that describes the angle of an aircraft body and wings relative to its actual flightpath. During maneuvers, pilots often fly at extreme angles of attack -- with the nose pitched up while the aircraft continues in its original direction. This can lead to conditions in which the airflow becomes separated over large regions of the lifting surfaces (airfoils). These conditions can result in insufficient lift to maintain altitude or control of the aircraft and a corresponding increase in drag -- a condition known as stall. (In an ideal situation, the airflow would remain attached to the airfoil surface from leading to trailing edge; this would reduce the drag that impedes the movement of the airfoil through the atmosphere. When the airflow separates from the surface, this increases the drag and can lead to a stall.)

The HARV was developed from a pre-production model of the F-18, a single-seat fighter aircraft built by the McDonnell Aircraft Company, St. Louis, Missouri. This particular F-18, built before the redesignation of the aircraft to F/A-18, was borrowed from the U.S. Navy for high angle of attack research because it was equipped with a spin chute, having been used by the Navy for spin testing. Bearing Bureau Number 160780, this F-18 was the sixth full-scale developmental F-18 built for the Navy by McDonnell Douglas Corporation (St. Louis, Missouri). F/A-18 aircraft are currently in service with the U.S. Navy and Marine Corps.

The particular F-18 used for the HARV had unfortunately been heavily "cannibalized" (used as a source of spare parts) by the Navy, which never expected the aircraft would fly again. It arrived at Dryden in pieces aboard a semitrailer in October 1984, missing 400 parts and having very little documentation on its existing wiring system. Dryden mechanics and technicians had to find substitute parts, cut out all the existing wiring, then assemble the aircraft and rewire it. When they completed the job, they painted the words "Silk Purse" on the side of the fuselage to indicate what they had made from the "Sow's Ear" of cannibalized aircraft parts with which they had begun.

The movie clip runs about 15 seconds and shows the NASA F-18 High Alpha Research Vehicle flying in a low-speed/high angle-of-attack maneuver during the study of air flow over the vehicle and its effects, which can be seen in the small tufts of yarn and smoke released through ports in the aircraft nose.

F-18 HARV Project Home Page

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