Falcon 7X will let the wires do all the work

 - May 23, 2008, 6:54 AM

The Dassault Falcon 7X will be the first purpose-built business jet to have a fly-by-wire (FBW) system. Reduced crew workload, better aircraft performance and increased safety should be the major benefits, Dassault technical managers told AIN.

With Dassault being part of EADS, it shouldn’t come as a surprise that the 7X’s FBW system will have a design philosophy similar to that found on Airbus airliners. And it seems that corporate pilots are warming to FBW systems. In fact, an Airbus Corporate Jetliner pilot at an executive charter operator told AIN he was happy with the aircraft’s fly-by-wire technology. (The ACJ is a business jet derivative of the A319 and as such is not a “purpose built” design.)

“The first benefit of fly-by-wire technology is workload reduction, thanks to the autotrim,” explained Jean-Pierre Julian, flight control system integrator for the Falcon 7X program team. Using a side-stick controller, the pilot will fly a longitudinal load factor and a lateral roll rate.

However, “yaw control will be possible for sideslipping on approach,” Julian added. The software may automatically compensate for the asymmetric thrust that follows an engine failure, but “it will only soften the effect of the failure,” he said. “It will not hide it.”

FBW controls may also “help enhance flight characteristics,” Julian continued. Control-surface positioning will be optimized to reduce drag, and the static stability margin will be reduced for a corresponding reduction in fuel burn.

Flight-envelope limitations will include angle of attack/attitude, load factor and speed. “The latter means that the aircraft is protected against sustained flying above Mmo,” Julian explained. He also clarified that although the pilot cannot deliberately overshoot the attitude limitation, the aircraft can. “In case of strong turbulence that would force the aircraft into a dangerous attitude, the system would just make the aircraft recover,” he said.

Asked whether FBW and flight- envelope limitations were consistent with Dassault’s pilot-in-the-loop philosophy, Julian answered, “The pilot is still in the loop; fly-by-wire brings safety and peace of mind.” He stressed that load-factor limitations have been implemented on Dassault’s Rafale fighter for years. And “software and hardware architectures are derived from those of the Rafale,” according to Yves Davaine, Falcon 7X program director.

The Falcon 7X’s ergonomics and limitations should be close to those of the Airbus philosophy. “We discussed a lot with the Airbus people and found that we shared some views,” Julian said. For instance, side-stick controllers on the Falcon 7X will be “as close as possible” to Airbus’ in terms of control laws and priority logic. “Side-stick inputs will be added algebraically,” he said, but “a pilot can take full control by pushing a button.”

The new airplane’s development schedule calls for first flight in early 2005. To have FBW controls ready by then, Dassault engineers plan to build a testbed that “will not be an iron bird, but will be comprehensive enough for development and certification purposes,” Davaine said.

About one year before first flight, the flight controls team will deliver the entire equipment–computers, software and servo controls. A “marketing demonstrator” of the FBW cockpit system should be ready for next year’s NBAA Convention in Orlando, Fla.

Dassault wants the FBW controls to be “as reliable as today’s mechanical linkage controls on Falcons.” The targeted mean time between failure of the FBW system “is at least 2,000 flight hours.” Further, AOG failure probability should not be more than one out of 33,000 flight hours, Dassault said. “In addition, small failures should not prevent the Falcon from flying 50 more hours before troubleshooting,” Julian told AIN. Just as on the under-development Airbus A380, the Falcon 7X will have an electric backup system (a ram-air turbine generator), but no mechanical backup to the FBW system.

“Fly-by-wire brings fantastic precision in flying the aircraft,” contended Richard Cimino, head of the ACJ operation at French executive charter operator Aero Services. “You can position the aircraft on a one-degree nose-up attitude and it will keep it, regardless of turbulence,” he pointed out. Cimino added that flying with FBW controls “does not require any familiarization” and side-stick controllers give more room in front of the pilot to use a notepad or review charts. He also said he believes that “flight-envelope limitations enhance safety.”