Boeing and its suppliers have been gathering a wealth of experience from the 787’s operations with a more-electric architecture, but the prospects of seeing a business jet or a helicopter adopting a similar approach appear relatively dim. Compared with hydraulic or pneumatic systems, their electric equivalents still face challenges such as reliability, as well as power and energy density.

Dassault is conducting research and development work toward a more-electric architecture for a Falcon that could enter service in the 2020-2025 time frame. Engineers from the company and partners in Europe’s Clean Sky initiative are endeavoring to use fewer hydraulics and less engine bleed air, with the goal of improving overall efficiency. The installed electric power would thus be greater than today’s 50 kW on the Falcon 7X.

However, the predicted reliability of electric systems, especially for power electronics, is a road block. “The right level would be one failure every 10,000 flight hours, and this is 10 or 100 times greater than what we have today,” said Jean-Marc Le Peuvédic, Dassault’s on-board energy architect for future systems, at the More-Electric Aircraft 2015 conference, held in Toulouse, France, earlier this year.

He noted the automotive industry has solved the problem not only by improving the technology but also by changing its predictive analysis method.

Hot temperatures degrade component reliability, so validation of a thermal modeling software program–even for transient temperatures–is crucial. Validation trials are taking place at a Fraunhofer-IBP test facility in Stuttgart, Germany. Reducing the need for cooling would help, too, as cooling circuits contribute to drag. Dassault also uses a testbed operated near Paris by Labinal Power Systems, which recently gave the rig full DC architecture.

Replacing hydraulics with electric power is already recognized for its environmental benefit, since hydraulic fluids are hazardous–more so at the production stage, Le Peuvédic noted, than during the aircraft’s operational life. “During manufacturing, we open and close the hydraulic system several times for testing,” he said.

The need for more wiring could raise weight, but choosing aluminum instead of copper might balance that out. Le Peuvédic cited the operating noise of electric systems as a specific issue that must be addressed to ensure the quiet cabin owners of business jets expect.

Hybrid Systems in Operation

Despite these obstacles, the move toward more-electric systems has begun. On the in-development Falcon 5X, an electric starter replaces a conventional pneumatic one. A Thales executive explained that the new Snecma Silvercrest turbofan has a high pressure ratio and a large fan to meet the goal of reducing fuel burn, “and this requires strong torque at start-up, which only an electric motor can meet.”

Meanwhile, the first auxiliary power unit (APU) designed from the outset for more-electric architectures has entered service on a helicopter. The Microturbo e-APU60 has been aboard the AgustaWestland AW189 twin since last year. The e-APU60 delivers 60 kilowatts and is certified in category 1, which means it can be used in flight for engine restart or for supplying electricity to some systems after failure of a generator. The 121-pound e-APU also can supply 50 psi of bleed air at a flow of 17 pounds per minute. It can operate at up to 20,000 feet, from -50 degrees C to +60 degrees C.

Liebherr Aerospace has completed testing an electromechanical actuator for a helicopter wheeled landing gear. Such a system would eliminate hydraulic lines around the cabin and reduce environmental impact and operating costs. Challenges lie in safety (notably for emergency extension), reliability and weight, as well as volume. Liebherr designed and built the prototype of a 4.6-foot-long actuator (retracted) in just four months. Test results show “good correspondence with the design targets,” according to the company. Both Airbus Helicopters and AgustaWestland are said to have shown interest.

Apart from the APU, a more-electric architecture is unlikely to appear on a helicopter any time soon. The electric backup system Airbus Helicopters (then Eurocopter) successfully tested in 2011 to make autorotations safer did not enter production. The system’s weight (equivalent to one passenger) thwarted that ambition. The motor’s power density (measured in kW/lb) just met the required level but the battery’s power density (kWh/lb) was inadequate, according to Airbus Helicopters. Continued progress in battery technology will yield a suitable power density by 2020, Airbus experts predict.

Another way to introduce a “mild hybrid” architecture–in the 100- to 300-kW range–would be at the tail rotor. An electric tail rotor would eliminate the complex and heavy mechanical linkage with the main rotor, and decoupling the two rotors’ rotational speeds could unlock some efficiency gains. However, the motor, converter and generator for such a tail rotor would incur a weight penalty of more than 150 pounds. Airbus Helicopters engineers say the configuration would have to shed 80 percent of that weight gain before they could adopt it for a production helicopter.