Northrop Grumman and the US Navy successfully completed the second and third flights of the X-47B unmanned combat air system, less than a month after the X-47B first flew.
The flights were conducted at Edwards Air Force Base and mark the beginning of the envelope expansion process of flight testing, whereby the test team will begin proving that the tailless aircraft can perform safely over a broad range of altitudes, air speeds and operating weights.
During the X-47B’s 39-minute second flight on March 1, the aircraft flew to an altitude of 7 500 feet at speeds up to 200 knots. During its 41-minute third flight on March 4, the aircraft reached an altitude of 7 500 feet and a top speed of 180 knots. By comparison, the X-47B flew only to 5,000 feet at a top speed of 180 knots during its first flight on February 4.
“Conducting two flights of a brand new type of aircraft within one week, and both within a month of first flight speaks not only to the robust design of the X-47B aircraft, but also to the dedication and engineering skills of the joint UCAS-D flight test team,” said Janis Pamiljans, vice president for the Navy UCAS program for Northrop Grumman’s Aerospace Systems sector. “These flights continue to add momentum to the team’s march toward demonstrating in 2013 that we can safely operate this tailless, low-observable-relevant air system on a Navy aircraft carrier.”
According to Phil Saunders, chief engineer for Northrop Grumman’s Navy UCAS program, envelope expansion is designed to fully characterize the aircraft’s flying qualities and prove that they match the system’s performance requirements and the test team’s predictions.
“Over the next few flights, we’ll continue to expand the envelope in terms of air speed, altitude and operating weight range,” he said. “By gradually ramping up the complexity of requirements, we will systematically prove that this air system can safely take off, fly and land in all anticipated flight environments.”
Northrop Grumman and the Navy expect to complete the planned 49-flight envelope expansion program at Edwards Air Force Base before moving the first X-47B to Naval Air Station Patuxent River, Maryland, later this year, he added. The X-47B will eventually be hoisted onboard an aircraft carrier. The UCAS will then be manoeuvred around the ship as part of carrier deck operations and handling trials. Carrier landings will take place in 2013 rather than late 2011 as originally planned.
One of the most important measures of performance, Saunders explains, is aircraft stability. The X-47B, which relies on high-speed computers to manage its flight control surfaces, must be able to adjust quickly and automatically to unpredictable environmental conditions such as air turbulence or cross winds. The recent test flights included a series of manoeuvres designed to measure the aircraft’s ability to maintain a smooth, level flying state in the presence of such conditions.
The flight tests also confirmed that the X-47B’s flush mounted air data system – a nod to its low-observable design – is accurately sensing and communicating the aircraft’s air speed, a critical factor in takeoff and landing. The X-47 is the US Navy’s first dedicated stealth aircraft since the General Dynamics/McDonnell Douglas A-12, which was cancelled in 1991.
In addition, the flight tests gave the team the opportunity to validate the aircraft’s engine performance; its command and control system, and its ability to fly at a constant angle of attack and a constant rate of descent while on final approach to landing, simulating what it will have to do to make successful landing on an aircraft carrier.
The Navy awarded the UCAS-D prime contract to Northrop Grumman in August 2007. The six-year contract calls for the development of two X-47B fighter-sized aircraft. The program will demonstrate the first-ever carrier launches and recoveries by a tailless, unmanned aircraft. Autonomous aerial refuelling will also be performed after carrier integration and at-sea trials.
The X-47 project started out under the Defence Advanced Research Projects Agency’s (DARPA) Joint Unmanned Combat Air Systems (J-UCAS) programme, and first flew in February 2003. In February 2006 the J-UCAS programme was cancelled but in August 2007 the US Navy selected the X-47B with Pratt & Whitney F100-PW-229 engine for its Unmanned Combat Air Systems Demonstration (UCAS-D) project to create a carrier-based unmanned aircraft.
The first X-47B, Air Vehicle 1 (AV-1), was rolled out in December 2008 but the start of flight tests has been delayed by engine-related acoustic and starting problems and software complexity. The X-47B was originally due to fly in November 2009 but Northrop Grumman and the US Navy only passed the aircraft for taxi tests at a flight readiness review in early November 2010.
The second X-47B, AV-2, has been transferred to a loads testing rig where it will undergo structural proof tests that will simulate carrier landing and critical flight loads, as well as check the structure for catapult and arrestment loads, fuel system integrity and control surface freedom under load.
The second X-47B incorporates design improvements to the engine nozzle structure in order to rectify issues with the acoustics that arose from the X-47B’s Pratt & Whitney F100-220U engine that contributed to delays to AV-1. AV-2 will make its first flight at Edwards toward the end of the year.