The Vectoring Extremely Short Takeoff and Landing Control Tailless Operation Research (VECTOR) X-31 flight test program completed the final flight of its lengthy "up-and-away" test phase March 22, clearing the way for the final phase of flight test to begin any day. By the end of April, the team hopes to have flown the world’s first thrust-vectored, automated landings on the runway.

The X-31 uses thrust vectoring – controlling the direction of its engine exhaust with paddle-like vanes to maintain control at high angles of attack and reduced speeds, even well below the typical landing speed for an aircraft of its type.

The Navy is using the X-31 to explore applications of thrust vectoring technology for extremely short takeoff and landing (ESTOL), with a particular eye toward the carrier landing environment. Naval Air Systems Command (NAVAIR) has partnered on the VECTOR program with Germany's Federal Office of Defense Technology and Procurement, European Aeronautic Defence and Space (EADS) Company and Boeing Aerospace.

In May, the test team began flying the "ESTOL up-and-away" test phase, which centered around flying ESTOL approaches to a "virtual runway" at 5,000 feet, successfully validating the technique. During the 51 flights for “up-and-away” testing, X-31 test pilots flew ESTOL approaches at altitude to a maximum of 28 degrees angle of attack, said Doug Wilkin, lead flight test engineer for VECTOR.

The X-31 is also being used as a test bed for EADS' Flush Air Data System (FADS), a nose-mounted sensor that measures local pressures used to calculate airspeed, angle of attack, sideslip and altitude information, Wilkin said. The FADS has been hailed as a more accurate, more stealthy alternative to the pitot static probes and ports commonly used on aircraft today, he added.

German Naval Reserve Cmdr. Rüdiger Knöpfel closed out ESTOL up-and-away March 22 with two supersonic flights focused on assessing FADS performance. He reached speeds of Mach 1.06 and 1.18, in full afterburner at 39,000 feet, he said. While supersonic, he induced combinations of angle of attack and side slip to tax the FADS. By that night, Wilkin added, engineers had processed the data and were able to confirm that the FADS was performing as desired throughout the flight regime.

Another highlight of the up-and-away flight test phase was flying the X-31 at 70 degrees angle of attack to gather FADS performance data, Wilkin said. At 70 degrees angle of attack, the X-31 can fly parallel to the horizon while its nose is pointed almost straight up at the sky.

The X-31 is now being prepared for the final "ESTOL-to-ground" test phase, in which Knopfel and his American counterpart, Marine Corps Maj. Cody Allee, will guide the aircraft through its complex ESTOL landing maneuver at increasing angles of attack and associated reductions in speed.

Currently, the fly-by-wire X-31 is receiving a new software load for its flight control computers, one that includes the control laws for the ground landing. The team is also making slight airframe modifications, and expects to begin flying again during the first week of April, said Harvey Henn, flight test director. They expect to accomplish all their goals within 14 flights, with the first ESTOL landing occurring around the eighth flight, he said.

Demonstrating the feasibility of thrust-vectored ESTOL landings could give Navy planners an important set of options as they shape acquisition decisions over the coming decades, program officials believe. In the fleet, landings at reduced speeds and subsequently higher angles of attack would impart significantly reduced forces to both the aircraft and, in the case of carrier landings, the arresting gear on the ship, said VECTOR Program Manager Jennifer Young.

Besides reducing fatigue and increasing system life, such reduced-energy landings would permit aircraft to land heavier, bringing weapons and fuel back to the ship that might otherwise need to be jettisoned, she explained. ESTOL may also have applications for unmanned aerial vehicles. [ANN Thanks James Darcy, Naval Air Station Patuxent River PA]

FMI: www.news.navy.mil/local/navair