The G650's high-level Normal Laws, hosted by the dual primary flight control computers, are quite similar to those of the Boeing 787. The basic pitch law is similar to the 787's C*U design. C* means that fore/aft yoke movement commands pitch rate by means of a simple Direct Law mode on the ground and vertical acceleration, or g rate, in the air using several inputs to the FCCs. U means that the aircraft is speed stable, so the pilot must trim nose up or down with speed change.
Three-axis stability augmentation makes the aircraft easy to fly because it compensates for trim changes caused by control surface or landing gear extension or retraction. Similar to the 787, the G650's FBW system has a maneuver load alleviation function that progressively deflects the ailerons and outboard spoilers at 1.5 g's and above to reduce the lift produced by the outboard wing sections and thus the wing bending moment. Other high-level control functions include automatic retraction of the speed brakes under certain conditions, dynamic rudder travel limiting to prevent overstress of the vertical fin, and elevator split limiting to prevent overstress of the empennage.
Similar to Boeing and Embraer FBW designs, the G650 has no hard limits on pitch or roll angles. However, the system does have hard limit maximum AOA and high-speed flight envelope protections in the Normal Law mode.
If air data or IRS information is insufficient or not available, the FCCs revert to Alternate Law mode. The autopilot becomes inoperative and flight envelope protections are degraded. If all four channels of the primary FCCs are unavailable, the FBW system reverts to Direct Law mode in which the control surfaces respond directly and proportionately to cockpit flight control inputs.
Bombardier has announced that its two new ultra-long-range, high-speed business jets, the Global 7000 and Global 8000, will be fitted with FBW controls. Many components will be supplied by Parker Aerospace.
Many other general aviation manufacturers are likely to follow. Most early adopters will fit FBW controls to aircraft that otherwise would require conventional powered flight control surface actuators. But future light and medium business aircraft may feature some form of FBW because maneuver load alleviation and flight envelope protection may enable engineers to reduce structural weight, thereby improving fuel efficiency and increasing tanks-full payload.
Plainly put, FBW aircraft are easier to fly than aircraft with conventional flight controls. Optimum stability and control response characteristics can be written into the high-level primary flight control computer software codes, transforming a marginally stable, but aerodynamically superior airplane into the most docile handling ship in the air. Flight envelope protections enable pilots to fly the aircraft closer to stall and high-speed margins so that they can safely, consistently and confidently extract more performance out of the aircraft when needed.
But potential aircraft design and development cost reduction is the main incentive for airframe manufacturers. Future designs can be lighter weight, more aerodynamically efficient and even longer lasting because of FBW's stability augmentation, maneuver load alleviation and flight envelope protection capabilities. Flight test development programs should be shorter because FBW software will assure that aircraft consistently meet stability and control standards set by airworthiness certification authorities. Any shortcomings on the path to certification will be corrected by rewriting code in a few hours rather than having to paste on new aerodynamic bandages such as vortex generators, stall strips and wing fences.
In a few of decades, fly-by-wire on new turbine aircraft could become as common as throttle-by-wire, steer-by-wire and brake-by-wire on current aircraft. That development could make new models so much more efficient, as well as easier to fly than older models, that fleet replacement might accelerate at an unprecedented pace. BCA