During a visit to Parker Aerospace’s Irvine, Calif., Control Systems Division recently, AIN took a tour through the fly-by-wire flight control systems integration laboratory and received briefing on modern flight control technology. Parker officials also provided information about the company’s work on the Embraer Legacy 450/500 program, which suffered a delay due to changes to the flight control system.
Parker makes the new Legacy jet’s full closed-loop fly-by-wire (FBW) flight control system, “from stick to surface.” As team leader for the flight control system, the Control Systems Division is responsible for system architecture development and integration testing and supporting failure hazard assessment and certification plan development. Parker is currently working on six major FBW programs.
“We predict that all future military, commercial transport, regional and large business aircraft will use fly-by-wire systems,” said David McLaughlin, chief engineer, flight control systems. Among the advantages are lower aircraft weight, as FBW computers use the flight controls to reduce maneuvering loads on the airframe. “This is one of the biggest attributes of the fly-by-wire system,” he said.
The other key attribute is envelope protection, which prevents pilots from exceeding certain parameters and can also help them stay well within the safest areas of the normal flight envelope, reducing workload. The Legacy 450/500, for example, will allow pilots to exceed the “soft” limits of the normal flight envelope (pitch +30/-15 degrees, bank angle 33 degrees, Mmo/Vmo and a limit of 1.1 times the stall speed). The pilots know that the aircraft is exceeding these limits because they have to maintain pressure on the stick to fly outside the soft limits.
Instead of a stick pusher, the Legacy FBW system uses an angle-of-attack limiter. This allows lower takeoff and landing speeds and improved runway performance, by reducing margins over the stall speed. If the pilot needs a maximum climb, say, for wind-shear or obstacle avoidance, it is necessary only to pull the stick all the way aft and the airplane pitches up as much as possible while protecting against exceeding maximum load factor and stalling. The FBW system minimizes turbulence effects, reducing oscillations, giving passengers a more comfortable ride.
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Parker Aerospace Control Systems makes FBW and other flight control equipment for a variety of business jet, airliner and military programs. These include the Gulfstream G650, Embraer Legacy 450/500 and 170/190/Lineage 1000, and Bombardier Global 7000/8000 and CSeries. The Legacy is an example of a full stick-to-surface program, where Parker is responsible for all flight-control hardware and software from the control stick to the flight control surfaces. Parker also makes the Legacy’s hydraulic and fuel systems.
Development of a complex full-FBW system such as the Legacy’s begins shortly after the program is launched and runs concurrently through certification. The process begins with defining requirements, followed by designing the system, sub-systems and components. Next comes production of hardware, firmware and software and integration of these, followed by validation and verification (V&V) testing in the lab, where actuators are run through thousands of cycles of operation. Qualification testing covers electromagnetic interference, high-intensity radiated field, lightning and other environmental tests. And finally, all of the systems must meet industry performance standards.
While the Legacy FBW involves 4.5 years of work (including a one-year delay), the effort benefits an OEM that plans to use FBW technology in later designs. Obviously the Legacy 500, which flew first, shares nearly the exact same components and architecture of the Legacy 450 FBW system. The same is true in Bombardier’s case; much of the FBW system for the CSeries airliner is directly transferable to the Global 7000/8000 flight control system. “There are architecture changes that occur,” said Parker chief engineer Glenn Zwicker. “[But we can reuse] a major portion of the software with just module changes and parameter changes.”
Parker engineers have compressed the time needed in the lab considerably, according to senior aerospace project engineer Dominic D’souza. On the Legacy stick-to-surface FBW system, about 300 test procedures need to be done to satisfy about 3,000 post-first-flight system requirements. “Any [other] company would take about a year to run those test procedures,” he said. “We’ve automated all those procedures and we’re trying to run it in as little as five weeks on two setups–24/7–including our team in Bangalore, India, that runs at night and on weekends.”
On a non-FBW jet, approximately 200 flight-control communications signals normally travel along the databus in the aircraft. But the number of signals grows exponentially with FBW, and on a jet such as the Legacy 450/500, more than 70,000 signals move through two databuses (a proprietary TTTech bus and Arinc 429).
The huge number of signals is the result of all the work involved in translating the movements of the pilots’ sidesticks into actuation of the flight controls. The analog signals from the sidesticks and other switches such as flap and spoiler levers are converted to digital signals by inceptor interface modules. Digital signals move to flight control computers (designed by Parker and made by BAE Systems) then through remote electronic units to the primary control unit at the flight controls. This is usually an electrically driven, hydraulically powered actuator, and there can be more than a dozen in an FBW business jet. Other components include an alternate flight control unit, which bypasses the flight control computers in case these run into problems, and motor control electronics for electrically actuated flaps.
“There’s a lot of complexity with what used to be a simple requirement,” D’souza said.
“Our differentiator is the speed by which we’re going to get better, faster and lower-cost as we go from one platform to the next,” said Parker Control Systems director of marketing Michael Engers.
The future of aircraft development looks like a lot more fully digital, three-axis FBW, according to David McLaughlin, Parker chief engineer, flight control systems.
Sidestick controllers will become more widespread (Gulfstream’s G650 has yokes, as do all Boeing FBW jets). According to McLaughlin, several OEMs are already working on incorporating sidesticks that contain active feedback mechanisms. “We see further advancements in control laws,” he added. “Control laws are really where you have significant opportunities to gain efficiencies and weight reduction. We’ll see broader use of load alleviation and envelope protection.” Another promising area is reducing the size of FBW electronics.