By Douglas Nelms
The U.S. Army’s first total fly-by-wire helicopter is still on schedule in its developmental testing (DT) phase, despite rumors that the program has been delayed by technical problems, according to Col. Neil Thurgood, project manager for utility helicopters. The UH-60 upgrade program was started in 2004, with the first of two prototypes flown in 2008. Those aircraft are now undergoing DT at Sikorsky’s test facility in West Palm Beach, Fla.
As of late 2009, the test UH-60s had flown more than 190 hours into a 400-hour flight test program, “so we are where we need to be, flying the software loads that we are supposed to be flying per the schedule,” Thurgood said. The first flight had been delayed by about eight months because of software development problems caused by the difficulty of adapting FBW to the many dynamic flight surfaces of a helicopter. “It’s very different than you would see in a (fixed-wing) jet,” he said. A spokesperson from Sikorsky noted that the software issues “are behind us.”
The FBW system will provide triple redundancy, with wires going from the cyclic, collective and pedals to computerized active servos on the main and anti-torque rotors. These change the electronic signals into hydraulic signals, which drive the control links of the two rotor systems. Development of the FBW UH-60 came about because of a requirement by the Army to improve stability and controllability in the helicopter in a “degraded visual environment (DVE),” with FBW being part of the U-60 modernization program, Thurgood said.
Sikorsky is prime contractor and has developed the FBW system. The cockpit will be a digital “glass” cockpit using a Rockwell Collins Common Avionics Architecture System (CAAS) with Hamilton Sundstrand dual-channel flight control computers and actuators, and BAe Systems active control sticks. The aircraft will also have upgraded GE T700-701E engines with full-authority digital engine control (FADEC), something not on the current UH-60M Black Hawk in use with the Army. In answering the question of any technical problems threatening the UH-60 upgrade FBW program, Thurgood said that there is a tendency “for people to confuse normal issues associated with developmental tests as big technical issues. But that’s why we do DTs, to find [and resolve] those issues. The aircraft are doing quite well and there are no technical issues that are threatening [the program].”
If Sikorsky receives the “go ahead” for the upgraded Black Hawk, the Army has indicated a need for 900 FBW-equipped aircraft. “We will continue on the DT tests at least until 2012,” Thurgood said.
Sikorsky said it would continue its development testing through 2010, then deliver the two aircraft to the government for further evaluation. The Army was expected to make a decision on low rate initial production in late 2009, which would affect FY11 and FY12 funding depending on that decision. Sikorsky’s experience with FBW comes from its development of the system for the H-92 (military version of the S-92) sold to the Canadian Military Forces. AgustaWestland has worked on developing FBW for its EH-101, working with BAe Systems and Claverham for its helicopter electro actuation technology (HEAT).
HEAT was designed to replace the complete EH-101’s hydraulic actuator system with electrical actuation as part of the British Royal Navy’s AW101 Merlin capability sustainment program. However, because of technical issues that developed, the British MoD cancelled HEAT for MCSP. Prime MCSP contractor was Lockheed Martin UK.
Boeing developed the world’s first true fly-by-wire helicopter in the late 1960s/early 1970s for the planned XCH-62 heavy lift helicopter under the Army’s Tactical Aircraft Guidance System (TAGS), using a FBW CH-47B Chinook testbed. However, that program was cancelled. Boeing is still working on developing fly-by-wire capabilities with its digital advance flight control system (DAFCS) for the CH-47F. While not true FBW, it provides roughly 80 percent of FBW capabilities at 20 percent of the cost, according to Mark Ballew, Boeing’s manager, tandem rotor products. This is particularly used in the aircraft’s automatic hover hold system. The Bell/Boeing V-22 is FBW, although not strictly considered a helicopter.