RELEASE: 01-040February 28, 2001

Successful first flight for VECTOR, X-31 at Pax

By James Darcy
NAS Patuxent River Public Affairs Department

PATUXENT RIVER NAVAL AIR STATION, MD-The X-31 concept demonstrator made its first flight since 1995 on Feb. 24 here, beginning a new era of flight test for the one-of-a-kind jet. The X-31 uses thrust vectoring - controlling the direction of its engine exhaust with paddle-like vanes - to maintain control at speeds and angles that would otherwise induce stall. The plane demonstrated the combat utility of thrust vectoring in the early 1990s during the Enhanced Fighter Maneuverability project, but was brought out of retirement last year and reconfigured for the Navy's international VECTOR test program.

According to program manager Jennifer Young, VECTOR will explore the uses of thrust vectoring for extremely short takeoff and landing (ESTOL), particularly with application in the carrier landing environment. VECTOR is a joint venture of the Navy, Boeing Aerospace, Germany's federal defense procurement agency (BWB), and European Aeronautic Defence and Space (EADS) Military Aircraft.

During Saturday's 38-minute functional check flight, Cmdr. Vivan "Noodles" Ragusa piloted the aircraft to a speed of 400 knots at altitudes up to 10,000 feet, and attained a thirty-degree angle of attack without using vectored thrust. Ragusa is assigned to Naval Strike Aircraft Test Squadron, which has custody of the X-31 during VECTOR. He shares piloting duties with German test pilot Ruediger "Rudy" Knoepfel. Boeing test pilot Ricardo Traven flew the chase plane, an F/A-18 from Strike.

The X-31 is scheduled to fly again within the week, following high power engine runs at Pax River's Aircraft Test and Evaluation Facility. Over the next six weeks, the test team will complete a thorough checkout of all of the aircraft's systems, and will calibrate the flight control system to the unique characteristics of the engine's exhaust plume. The initial flights will also yield baseline data for the design of new ESTOL software for the digital flight control system, added Flight Test Director Paul Conigliaro.

Without benefit of digital flight control computers to stabilize the aircraft and translate pilot inputs into the proper coordination of control surfaces and thrust vectoring vanes, the aircraft would quickly become unstable.

Following the initial six-week flight period, the aircraft will begin preparations for the second major test phase, dubbed "ESTOL up-and-away."

"Basically, the pilots will be flying to landings on a virtual runway in the sky," Conigliaro said. Only when the techniques of thrust-vectored, extremely short landings have been mastered at safe altitudes will the final "ESTOL to ground" test phase proceed.

When the X-31 does make its first ESTOL landing, it will use vectored thrust to fly a dramatic high-angle, reduced speed approach. "By increasing the approach angle of attack, from 12 degrees up to a maximum of 40 degrees, we'll be reducing [approach speed] by over 30 percent," Conigliaro said. "The art of this is that you want to put the engine nozzle about two feet above the runway, and then de-rotate the plane and touch down the wheels."

A video camera in the belly of the plane will provide feedback to the pilot via a cockpit display. However, during final approach the plane will be controlled by the autopilot, using combined inertial navigation system and global positioning system data to control the aircraft's location to within centimeters.

In the carrier landing environment to which the ESTOL technology might someday transition, a small reduction in landing speed could make a difference of 500 or 1000 pounds in bring-back weight.

"That's a weapon you didn't have to get rid of, or extra fuel you can carry that could save you a trip to the tanker," Conigliaro said.

Reduced landing speeds also translate into less wear and tear for the aircraft and arresting gear, as well as reduced wind-over-deck requirement for the ship. ESTOL may also see applications in unmanned aerial vehicles operating from fleet vessels.

In addition to exploring the ESTOL envelope, VECTOR will also test two versions of an Advanced Air Data System (AADS) designed and built by EADS. The system employs flush mounted air pressure sensors around the tip of the nose cone to maintain accurate speed and attitude measurements at high angles of attack.

Although the VECTOR program will finish up in 2002, the X-31 may continue to fly at Pax River under additional test programs currently under consideration. Pax River, which is home to the Naval Air Systems Command and Naval Air Warfare Center Aircraft Division, is gaining a reputation as a center of X-plane excellence. Lockheed Martin's X-35C, their Joint Strike Fighter (JSF) carrier variant, is stationed at Pax River for simulated carrier landing and approach tests, flying qualities analysis and other performance testing. Later this year, Boeing's X-32B, the contractor's short takeoff, vertical landing JSF demonstrator, will arrive here for testing at Pax River's unique hover pit facility.


POC Name: John RomerPOC Tel: 301-342-7710