Upstarts favor electric while establishment sits on fence
Business jet manufacturers do not agree on the virtues of electric power for onboard systems. Although Boeing and Airbus airliners are already going “more electric,” Dassault, Raytheon and Gulfstream remain cool about the claimed advantages of electricity versus hydraulic or pneumatic power. New entrants in the purpose-built bizjet arena, such as Eclipse Aviation, Embraer and Spectrum Aeronautical, are much more enthusiastic. The jets they are developing in the very light and light segments use electric air conditioning, landing-gear actuation or engine start, among others.
On the Boeing 787, arguably the most electric of all civil airplanes either existing or under development, the pressurization system uses electric compressors. The de-icing system uses electrical resistance to heat the wing leading edges in lieu of
hot engine bleed air. The boost pumps in the fuel system are electric as well. The engine starters are electrically–instead of pneumatically–powered by the auxiliary power unit (APU). The brakes are all-electric, too.
In a radical move, Boeing is taking advantage of the miniaturization of and recent progress in the reliability of high-power electronic components. The Chicago-based aerospace giant claims that this new architecture will simplify power distribution and improve safety too. For example, the electric system suppresses the risk of hydraulic leakage and subsequent fire. The new system should also provide a weight advantage, as hydraulic and pneumatic tubing is eliminated.
Finally, no pneumatic power means bleedless engines. This translates into better compressor efficiency and lower fuel burn. However, this shift does call for the installation of significant electric power production capabilities; in fact, the six generators the engines and the APU drive have a combined power close to 1.5 megawatts. The 787 will enter service in 2008.
OEMs Go Slow
So how do the well established bizjet manufacturers regard what appears to be a major shift in systems design? Surprisingly, none among Dassault, Raytheon Aircraft and Gulfstream seem warm to the idea of introducing more electric systems on their airplanes. Neither Cessna nor Bombardier delivered after AIN requested interviews with technical experts.
According to Bernard Baldini, a Dassault project manager in advanced design, the goal behind making an aircraft more electric must be “optimizing energy exchanges.” But before electric systems can contribute to this optimization, says Baldini, they will have to be lighter and more reliable. Baldini believes that flight control actuators will require much effort.
Electric systems are also not yet ready for cabin air conditioning, Baldini asserted. On a Falcon, 44 pounds of compressed air per minute is bled from the engine for cabin air conditioning purposes. The equivalent power– 6 kilowatts–is just a fraction of the 40 kilowatts an electric air-conditioning system would consume.
Would the de-icing system be a better candidate for electricity? Not really, Baldini suggested. Certified pneumatic systems fall short of being power-optimized, consuming as they do more than 150 pounds per minute of bleed air for just 40-percent efficiency. But integrating an electric wing anti/de-icing system on a small aircraft, such as a business jet, is highly complex. “A bizjet wing is thinner than that of a big airliner and therefore needs proportionally more de-icing power. The trade-off thus becomes a more difficult issue,” he explained. In addition, it would call for new, bleedless engines.
Although there is no near-term prospect for more-electric Falcons, the situation could change in the next few years. Dassault is involved in a European research project called More Open Electric Technologies. The $87 million (E70 million) Airbus-led project is starting this year. “Our interest is in the all-electric airplane,” a Dassault executive for advanced projects told AIN this summer. He said that business jet flight-control actuators need a relatively small amount of power. This would make it easier to move directly to electromechanical actuators, which–unlike electro-hydrostatic actuators–have no hydraulic back- up. “We believe we would get a significant maintenance advantage, although there might be a weight [penalty],” he noted. He added that the company must conduct an exhaustive study.
Raytheon’s director of advanced design, Sam Bruner, agrees with Dassault’s Baldini on the near-term perspective. “What would be the added value for the customer? At this point, we do not think it is appropriate to introduce more-electric systems,” he told AIN. Bruner explained that the weight savings on big airliners come from economies of scale. For example, an airliner has typically 10 times the length of plumbing a business jet has. Moreover, the process of converting mechanical energy to electric energy, which then has to be converted in some other form of energy, adds weight, he said.
Manufacturers Weigh Cost Benefits
Raytheon conducted a thorough cost study. It determined that converting some power from the engines into electricity was more expensive than using hot air directly. “The savings are worth it on a 787, but here, on business jets, the extra cost more than offsets the fuel saving,” Bruner said. In addition, Bruner does not see his customers accepting new systems while the current ones are what he terms “very robust.”
Yet both the Hawker 4000 and the Premier IA do feature an original, electrically powered de-icing system on their empennage. Equipment supplier Cox designed an electromechanical expulsion de-icing system. A microsecond-duration high-current electric pulse is delivered to the actuators inside the leading edge. It generates opposing electromagnetic fields that cause the actuators to change shape rapidly.
This change of the actuators’ shape is transmitted to the erosion shield of the leading edge, which flexes and vibrates at very high frequencies. This rapid motion results in acceleration-based debonding of accumulated ice on the erosion shield.
But this is apparently not the beginning of a wider use of electric power on Raytheon business jets. “On an Airbus or Boeing airplane, each additional passenger means more revenue; the way bizjets are used is different,” Bruner insisted.
Bill Whitton, Gulfstream’s aircraft systems engineering director, sounded a conservative note, too. In short, he believes more-electric technologies are not mature. “Our aircraft have 99.7-percent dispatch reliability, and our customers insist it stays that way,” he emphasized.
They also insist on safety and maintainability aspects, he added. “We are concerned that those systems’ lack of maturity would affect safety and their complexity would harm maintainability,” he said. For Gulfstream, the acknowledged weight benefit would not necessarily drive a good business case.
However, “Although we would not go for an all-electric aircraft, we could go shopping system by system,” Whitton said. For example, an application could be found in the short to mid-term for electro- hydraulic actuators. “They would bring some weight saving. And federated hydraulics are more robust as each actuator has its own hydraulic system,” he explained.
Matt Brown, Eclipse’s project manager for the Avio integrated avionics and electronic system, claimed the Eclipse 500 very light jet is the most electric of all general aviation aircraft. “We have no hydraulic system, except the brakes’ master cylinders,” he told AIN. The flight controls are mechanically actuated and even those few hydraulic systems are entirely self-contained. In other words, there are no hydraulic lines and thus no routine maintenance. Brown emphasized that the main benefit of a more-electric architecture is more centralized control of the aircraft’s systems.
Brown insisted that being innovative is compatible with the highest level of safety. “The Eclipse 500 is using high-fidelity electronic components with significantly higher lifecycles than more traditional, mechanical components,” he explained. And all critical avionics and electric systems are located inside the pressure vessel to protect them from temperature and pressure extremes.
The integrated electronic systems reduce redundancy-caused weight yet provide the redundancies needed. The Eclipse 500 has five independent electric buses. It has two generators on each engine and two back-up batteries.
Highly integrated electronic equipment also allows the Eclipse 500 to provide automatic load shedding. The Eclipse will power essential equipment for 30 minutes on battery power with the battery at only 85-percent life.
Separately, the Eclipse 500 de-icing system will feature new-generation boots but no electricity. “The situation is the same for the brakes; we would have certainly considered electric wing de-icing if it had been available during the design phase,” Brown said. Eclipse might consider replacing the boots with electrical resistance equipment as a future product improvement.
The electric systems should enhance ease of maintenance, too. Maintenance-intensive systems, such as high-pressure hydraulic systems, power brakes and thrust reversers are eliminated. Maintainability also benefits from the health monitoring enabled by extensive use of electronic components. The Eclipse 500 will enter service this year.
The Spectrum 33 VLJ also has a number of electric systems. “For example, the flap actuators and the landing-gear actuators are electric; the brakes are the only place for hydraulics,” Austin Blue, Spectrum Aeronautical’s vice president, told AIN. The start-up company intends to use a resistive de-icing system, Blue added.
Conventional window shades might be replaced on the Spectrum 33 with electrically dimmable windows (the Boeing 787 will feature such equipment) and bleed air will still be used for cabin pressurization.
Asked about the benefits of more-electric systems, Blue pointed out that “half of the unscheduled maintenance performed on airliners has to do with hydraulics.” Progress in the reliability of electric motors, he said, is now making hydraulics replacement possible. New program schedule details are expected next month, in the wake of the July fatal crash of a prototype.
Embraer More Conservative
Embraer seems to be pursuing a relatively conservative approach with its Phenom 100 very light jet and Phenom 300 light jet. The company has said only that its air conditioning systems will be bleedless and the Phenom 100’s hydraulic system will be electrically powered.
Without referring to a firm decision, Embraer estimated that “the ‘more electric’ concept is already mature in some applications–air conditioning, flight control actuators and main engine starting–for small business jets.” The company’s engineers expect that “other features, such as the ice protection system, will be technically feasible and commercially available in the near future.” The Phenom 100 and 300 are due to enter into service in 2008 and 2009, respectively.
The Brazilian-based manufacturer nevertheless has great expectations for the longer term. “We are evaluating the applicability of this concept in its full extent for future business jet programs,” the company said. Among other benefits, Embraer designers see simplification when electric harnesses replace hydraulic lines.
However, challenges remain, the Brazilians emphasize. Engines need to be redesigned to allow the more-electric concept, which requires significant power-shaft extraction in place of bleed-air extraction. The reliability of the electric power system, including generation and distribution, needs to be improved. Equipment needs to be tested exhaustively before it enters service, because even a small lack of cooling can significantly reduce reliability.