Thales is to provide quadruple-redundant computers for the Gulfstream G650’s fly-by-wire (FBW) flight controls. The new large-cabin, ultra-long-range business jet will be the first to feature Thales’ Quad-Dual architecture. While Thales will act as Gulfstream’s deputy, the aircraft manufacturer retains authority for FBW system integration.
According to Alain Boursier, general manager of Thales’ aerospace business in Canada, in 2004 Gulfstream selected the company for its advanced flight control research program, which eventually yielded the G650’s flight control configuration. It consists of two primary computers and a backup unit. The primary computers share work–unless one of them is totally out of action. In that case, the primary system reconfigures itself to a downgraded safe mode of operation.
Each of the main units contains two internal computers, also known as control lanes. Each control lane is built with a command lane and a monitor lane. When the monitor lane declares the command lane failed, the full control lane is declared failed. Then the primary flight control computer system reconfigures itself over the three remaining control lanes.
Boursier said that the system will detect an anomaly quickly, so the switch is unnoticeable to the user. The command and monitoring computers use different hardware and software, and each computer can command all flight controls.
The backup flight control unit–which employs still other hardware and software solutions–comes into play if both main units have failed. This unit is less powerful than the primary units. “It has get-home capability but does not provide sophisticated control laws,” Boursier said.
Therefore, flying with such direct control laws is not as easy for the pilot as flying with full FBW capabilities. Direct control laws are those where aerodynamic performance is transparent to the pilot. They link the pilot’s cockpit controls directly to the moving surface, with no computer middleman to manipulate handling qualities. “This is back to traditional piloting skills,” Boursier said. In addition, the ride for the passenger no longer benefits from the “smoothing effect” of the full FBW control laws, which usually can compensate for turbulence.
As Boursier pointed out, the level of redundancy of the G650’s FBW computers goes far beyond certification requirements. He believes that Thales’ architecture is more straightforward than those of its competitors while offering a similar level of redundancy. “For such systems, the target is one failure every billion flight hours,” he said.
Thales is assisting Gulfstream on the entire system’s design, and it is in charge of integrating flight control laws–which Gulfstream has specified–in the flight control computers. However, Boursier declined to be specific about the flight envelope protection.
While the aircraft manufacturer uses other suppliers, for the actuators, for example, Thales is in charge of integrating the entire system. This preliminary work is done on a testbed in Montreal. Thales is also responsible for electromagnetic interference qualification.
Actuators will be relatively old school: the aircraft now has a digital brain but its muscles are mostly hydraulic. Conventional flight controls use three hydraulic systems. On the G650, there are only two of them. The final level of redundancy is provided by backup hydraulic actuators moved by hydraulic pressure generated by an electric pump. These actuators have their own small hydraulic tank and thus do not rely on skeletal hydraulic fluid lines. Flight testing is under way on a Gulfstream V. “All concepts need to be validated before they’re fitted to the G650,” Boursier said.