New instrumentation for X-31

By JAMES DARCY
NAS Patuxent River Public Affairs Department

PATUXENT RIVER NAVAL AIR STATION, MD-The X-31 experimental aircraft is undergoing elective surgery, having a good portion of its brain swapped out for newer and better, and getting a few extra nerve endings for good measure.

The thrust-vectored X-31 is currently between flight test periods for the Navy's VECTOR concept demonstration program and is being fitted with new sensors, recording devices and telemetry equipment in preparation for more flights in the fall here.

The VECTOR team is removing old equipment from the X-31 and installing the Common Airborne Instrumentation System (CAIS), a set of devices to monitor, record and transmit data collected by sensors throughout the airframe. "We had a legacy system that was 15 years old and had used up its capacity," explained Paul Conigliaro, flight test director for the VECTOR program.

The old system, which was installed when the aircraft was built in the late 1980s, was larger and heavier but suited to the job at the time. It used a reel-to-reel tape recorder to store data collected by the X-31's myriad strain gauges, temperature and vibration sensors, accelerometers and position detectors.

"CAIS is the preferred Navy system now," said Dominic Scaduto, the instrumentation engineer responsible for the changeover. CAIS is a solid-state system with no moving parts. It records data into memory circuits rather than on the bulkier, less reliable tape. By installing the CAIS system, the VECTOR test team gains four times the data capacity while realizing at least 100 pounds in weight reduction, Scaduto said.

While every flight test program depends on the ability to monitor and record data, the demands of an X-plane project such as VECTOR are particularly high. The one-of-a-kind X-31 uses thrust vectoring - redirecting the engine's exhaust plume with a set of paddle-like vanes - to maintain lift and maneuverability at speeds and angles that would stall traditional aircraft. The pilot relies on a set of three flight control computers (FCCs), which track the aircraft's condition and provides the appropriate responses to his inputs on the stick and rudder.

"The airplane needs data to fly," Conigliaro said. Many of the sensors in the aircraft act like nerve endings for the FCCs, telling them what state the aircraft is in at any moment in time. But the sensors will also provide information to the CAIS, which not only records the data, but transmits it to the flight test controllers on the ground. For a typical test flight, the VECTOR team will have 10 or more engineers and one test pilot in the ground station control room.

"Primarily, the issue is safety," Conigliaro said. "The engineers on the ground are the primary backups for the

pilot." Together, they monitor or have access to hundreds of raw variables on the aircraft's status, as well as any number of other parameters instantly calculated from the raw data.

"The CAIS is just so fast and so versatile," Scaduto said. He estimates that he would have to install 120 extra gauges in the cockpit to give the pilot access to all the information that ground controllers receive during a flight.

Even if that were physically possible, the pilot would be overwhelmed with information. The ground controllers provide lots of extra eyeballs to look out for trouble, while the pilot can focus on just the most critical pieces of information.

Safety is only one consideration, however. The information gathered through the instrumentation will be a fundamental product for the VECTOR program, which is exploring the uses of thrust vectoring for extremely short takeoff and landing (ESTOL), particularly with regard to the carrier-landing environment. "We're here to get data," Scaduto said. "With instrumentation, you want to change a physical thing, such as temperature or vibration, into data, and then synchronize it into time."

Conigliaro offered the example of the new nose cone being installed on the aircraft in preparation for ESTOL flight. "The nose shape is a little different, so you assume the aircraft is going to fly a little differently," he said. But rather than rely on subjective pilot impressions, the VECTOR team could take accelerometer data from all over the aircraft and generate a "mode shape" - a detailed model of how the aircraft moves and vibrates as a whole at any point in time.

Other critical parameters include engine performance and how the FCCs "pass bits," or communicate with the aircraft, Scaduto said. The CAIS system will give the VECTOR team the speed and bandwidth they need over the next two years as they take the X-31 to portions of the flight envelope never before explored. When the X-31 makes the world's first thrust-vectored ESTOL landing in 2002, the CAIS system will be aboard, quietly monitoring the aircraft's vital signs while the VECTOR test team flies into the history books.

-USN-