Parker Aerospace: Fly-by-wire Is The Future

 - April 15, 2013, 8:30 PM
An artist’s concept depicts a Bombardier CS100 flying above the Great Wall; such an image could soon be a reality with that model or any of its competitors.

Parker Aerospace enjoys a wide reach in aviation manufacturing. It is likely that anyone who flew to Shanghai for this year’s ABACE show was on an aircraft that depends on a Parker system, whether flight controls, hydraulics, fuel, fluid conveyance, thermal management or engine components. In fact, the company is a key supplier for Comac’s ARJ21 regional jet and in-development C919 airliner.

Although Parker Aerospace (Booth P422) is headquartered in Irvine, California, it operates various other divisions in the U.S. that manufacture fluid management, hydraulic and control systems. Parker service centers are located throughout the world, including nine in the U.S. plus Beijing, Dubai, Kuala Lumpur, Brazil, Singapore and Germany. Parker Aerospace also has three engineering centers in Asia, including one here in Shanghai, as well as in Japan and India. During 2012, parent company Parker Hannifin had net sales of more than $13 billion, and the aerospace division–which employs some 6,000 workers–was responsible for $2 billion of that revenue.

Modern electronic fly-by-wire flight controls are developed and manufactured at Parker’s Irvine Control Systems division, and AIN was recently given a tour through the fly-by-wire flight control systems integration laboratory and a briefing on flight control technology.

An example of the Control Systems division’s work is the “stick to surface” full closed-loop fly-by-wire (FBW) flight control system for Embraer’s Legacy 450/500 program. 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. The advantages include allowing engineers to extract weight from aircraft structures because 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.

Envelope Protection

The other key attribute is envelope protection, which prevents pilots from exceeding certain parameters and can also help pilots stay well within the safest areas of the normal flight envelope, lowering their workload. An example of this is the Legacy 450/500, which will allow pilots to exceed the “soft” limits of the normal flight envelope. The pilot knows that these limits are being exceeded because he has to maintain pressure on the stick to fly outside the soft limits, for example, when he wants to bank the airplane more than 30 degrees.

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 windshear avoidance or to avoid an obstacle, he need only pull the stick all the way aft and the airplane pitches up as much as possible while the FBW system protects against exceeding maximum load factor and stalling. Turbulence effects are minimized by the FBW system reducing oscillations, giving passengers a more comfortable ride.

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 and Embraer Legacy 450/500 and 170/190/Lineage 1000, Bombardier Global 7000/8000 and CSeries and other airline and military programs. 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.

Complex Program

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, then designing the system, subsystems and components. Next comes production of hardware, firmware and software and integration of these, followed by validation and verification 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 development of FBW involves years of work, all that effort benefits an aircraft manufacturer that plans to use FBW technology in later designs. The Legacy 500, which flew first, has nearly the exact same components and architecture as 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.

On a non-FBW jet, about 200 flight control communications signals normally would travel along the databus in the aircraft. But the number of signals grows exponentially with FBW, and on a jet like the Legacy 450/500, upward of 70,000 signals move through two databuses.

The huge number of signals is because of all the work that must get done, 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, 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 a 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.

“Our differentiator is the speed by which we’re going to get better and faster with 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 McLaughlin. Sidestick controllers will become more widespread, although Gulfstream’s G650 has yokes, as do all Boeing FBW jets. “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,” he said, adding that another promising area is reducing the size of FBW electronics.