Unmanned Combat Aircraft Tests

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Spring 2012 at NAS Patuxent River, Md., and an unusual shape joins the F-35 Joint Strike Fighters flying the pattern at the U.S. Navy’s test center. The tailless flying wing is Northrop Grumman’s X-47B unmanned combat air system demonstrator (UCAS-D), being prepared for autonomous landings on an aircraft carrier in 2013.

The Navy may be late to the unmanned-aircraft game, but it is pushing the technology in terms of both capability and autonomy. In addition to UCAS-D, the service is launching the Autonomous Aerial Cargo/Utility System (Aacus) program to prototype advanced capabilities for vertical-takeoff-and-landing (VTOL) unmanned aircraft systems (UAS).

Just as Aacus is expected to feed technology into the Navy’s program to deploy the shipborne VTOL Medium-Range Multi-Role UAS by 2019, UCAS will inform its plans to field the Unmanned Carrier-Launched Airborne Surveillance and Strike System (Uclass) by 2018, and develop a sixth-generation F/A-XX to replace the Boeing F/A-18E/F after 2030.

Operational studies under the UCAS program have shown that a long-endurance, aerial-refueled unmanned combat aircraft could significantly extend the surveillance and strike reach of a carrier battle group. But first the Navy must get comfortable with bringing an unmanned aircraft on to the flightdeck.

Though UCAS-D is a demonstration, and not a prototype for Uclass, the system architecture and operating concepts developed to enable the 44,000-lb. X-47B to land safely on a carrier—and particularly changes to the ship’s command-and-control system—could carry over.

The first of two X-47Bs completed Block 1 envelope-expansion flight tests at Edwards AFB, Calif., on Nov. 17, and air vehicle 1 (AV-1) is to be shipped to Pax River by year-end to begin Block 2 carrier-suitability testing, including land-based catapult launches and arrested landings. The second X-47B, AV-2, made its first flight at Edwards on Nov. 22.

In 16 sorties since its initial flight on Feb. 4, AV-1 has expanded the envelope to 220 kt. airspeed and 15,000 ft. altitude—a task that was originally expected to take a year and require 49 flights. “AV-2 will continue to expand the envelope, and when it ships [to Pax River] all the necessary corners to go to the carrier will have been cleared,” says Carl Johnson, Northrop Grumman vice president and UCAS-D program manager.

While gathering flying-qualities data, AV-1 has flown simulated carrier approaches at altitude. “All X-47B flight-test data look very good and will support our carrier demonstration objectives,” says Capt. Jaime Engdahl, Navy UCAS program manager. “We found no technical issues during any of the flights and it took considerably less flight time than predicted to execute all of our planned test points.” As a result, AV-2 could be moved to NAS Pax early, in spring 2012.

The speed of envelope expansion is due in part to the accuracy and predictability with which the 62.1-ft.-wingspan X-47B executes the preprogrammed test points. But it is also due to Northrop’s familiarly with its signature cranked-kite planform, and to extensive modeling and simulation. Engdahl says the aircraft simulation model accounts for about a third of the 3.4 million lines of software code for the UCAS-D program.

“The modeling and simulation is correlating so well with flight-test data that we can use it to add confidence and reduce on-aircraft testing. It significantly reduced the number of flights required to expand the envelope,” says Johnson. “The future for UAS with robust modeling and simulation is we will not have to fly the platform as much as manned systems, which are less predictable.”