Gulfstream’s new fly-by-wire G500 and G600 are the first of the manufacturer’s business jets to be equipped with BAE Systems active inceptor sidesticks. The G650 is Gulfstream’s first jet with full fly-by-wire flight controls, but its cockpit is equipped with dual yokes that are mechanically interconnected. The BAE sidesticks are also connected and move together, but that connection is strictly electronic, not mechanical. What the BAE sidesticks do for Gulfstream is preserve simultaneous stick movement in a fly-by-wire environment, so both pilots still have the visual cue of seeing what the other pilot’s controls are doing at all times, while also preserving the feel of flying a Gulfstream jet.
Active sidesticks aren’t new, but they hadn’t made inroads in non-military applications, at least until Gulfstream chose them for the G500/G600 program. “We started developing active technology about 25 years ago,” said Adam Taylor, BAE Systems director of advanced inceptors. “People felt the loss of some of the feedback when aircraft went to fly-by-wire,” he explained. “As technologists, we’re looking at reintroducing that feedback.” In the early 1990s, the company began looking at how to provide that feedback to pilots, especially in the helicopter market.
This effort accelerated when active stick technology was specified for the Joint Strike Fighter, and BAE Systems designed the technology for both competing programs from Boeing and Lockheed. BAE began production of those active sidesticks in 2001, and then focused on the helicopter market. Meanwhile in 2004-05, Gulfstream approached BAE about the product. In the late 2000s, BAE had already begun developing its 5th generation active sidesticks, and then in 2010 Gulfstream announced it had selected the company to supply the active sidesticks for the new G500 and G600. These would be BAE’s fifth-generation active inceptor sidesticks.
The benefit of the sidesticks is not just seeing them both move together, but also tactile cueing, which electronically adds feel to the sticks. “We provide a set of software-programmable capabilities, and it’s up to the OEM to decide how to use them,” Taylor explained. “Commercial folks are absolutely aligned with the idea of linking them across the cockpit, where the copilot and pilot can feel and see movement of each other’s commands. The way Gulfstream uses [tactile cueing], they will have two soft stops in each axis, like a mini wall, so when you pull back or roll, you will feel a discrete change in gradient. Those soft stops move around in real time. [But] they are more subtle, and change the feel of the stick in real time; it’s not necessarily multiple soft stops.”
Another tactile cuing benefit, he added, is that “it can give performance benefits. It’s a very intuitive way of telling the pilot he’s close to the performance limit. You can allow the pilot to fly closer to those limits, and the pilot tends not to exceed them with tactile cuing; you don’t have to look at the gauges.” This feature explains how Gulfstream is able to make the G500/G600 flight controls replicate the feel of a typical large-cabin Gulfstream jet, unlike passive sidesticks, which have no tactile cuing or feel.
In terms of safety, just like any flight control system, including mechanical, hydraulic or fly-by-wire, the active sidesticks must meet the same requirements. These include 10 to the minus 9 safety and integrity numbers, Taylor said.
He explained that the active sidesticks contain sensors that detect the force applied by the pilot, and this is compared to a force-deflection gradient coming from the flight control computers. If the computer detects a certain amount of force, that corresponds to a specific displacement of the stick. “The real trick is we are looking at that all the time in real time,” he said, “and we can manipulate the relationship between the force applied and the movement of the stick. We do that with actuation system motors and gearboxes and multiple position-sensing channels. It includes, in case everything fails or we lose power on the aircraft, a passive backup mode, and we’re still left with a passive stick, which allows us to continue even if we lose most of the power on the aircraft.
“The key for Gulfstream,” Taylor said, “is they wanted to buy into the technology of the future, and going with active sidesticks allows them to future-proof their flight control solutions,” he said.