While Boeing has arguably taken the lead in more electric aircraft systems with the new 787 airliner, European manufacturers are trying to strike back. Airbus and a group of equipment makers have joined forces on European research projects to validate more electric technologies. The Power Optimized Aircraft (POA) was the first of these projects, initiated in 2002, while More Open Electrical Technologies (MOET) is now the follow-on.
Advances in high-power generation and power electronics reliability, combined with their miniaturization, are making electric systems worth comparing to their hydraulic and pneumatic counterparts. According to Liebherr Aerospace’s Lester Faleiro, POA project coordinator, there are many reasons to consider moving to electricity. “These systems are more efficient,” he told last month’s Paris forum on technologies for energy-optimized aircraft equipment systems (TEOS). For example, an electric ECS (environmental control system) consumes 14 percent less engine power than its pneumatic equivalent.
This is also true at the aircraft level. The aircraft may be heavier, because of the electric systems’ weight. It may also have more drag. This would result from the fact that conditioned air would not come from the engine but from an additional scoop on the aircraft. But the overall result benefits from the engines’ new freedom. Without the bleed off-take, specific fuel consumption (SFC) is improved.
Moreover, eliminating hydraulic fluids is good for the environment and the maintenance technicians. These fluids are highly flammable and a sudden leak can be dangerous simply because of the high pressure (3,000 or 5,000 psi). From a logistics standpoint, electric interfaces are easier. And moving to one main source of power reduces the variety of support equipment.
POA objectives included an unspecified reduction in total non-propulsive power and a 25-percent cut in peak non-propulsive power. It also included a five-percent reduction in fuel consumption and an unspecified reduction in total equipment weight. Faleiro considers all four objectives “achievable.” However, Airbus’ Etienne Foch, the MOET project coordinator, said “in the best case [depending on aircraft and mission], POA has shown a two-percent fuel saving.”
The Airbus A330-300 was chosen as the reference point. Electric current standard for the project is 350 Volts DC (direct current, as opposed to AC, alternating current). The in-production A330 uses 400 kVA of electric power. Should it move to an all-electric configuration, this figure would increase fourfold, to 1,600 kVA.
Electric generators better match peak power, Foch explained. They can use a combination of two strategies. The first one is giving them some overload capability. The second one is shedding some equipment. Combining the two avoids over sizing the generators.
Another benefit is reliability. It is much better to lose one electric actuator than a hydraulic one, which in turn has the entire network failing. “There is a difference of two orders of magnitude in reliability,” Foch emphasized.
However, many electric systems still have to be improved. For example, heater mats are considered mature for wing anti-icing but they need a lot of power. An electro-impulsive system is just the opposite–not mature but efficient. It saves up to 60 percent of power in climb and descent.
Another example is the 200 kW power electronics module that was exhibited at the forum. Designed by Thales Avionics Electrical Systems under the POA project, it weighs 190 pounds. It can be used to control an engine starter-generator, a fuel pump or ECS motor. Under the MOET project, Thales design engineers will endeavor to combine two of these three functions. “Common hardware accounts for two-thirds of the weight,” an engineer explained to Aviation International News.
POA followed a three-part process. The first one was the validation of systems. It answered the question: Are the components and systems we have chosen feasible? The second one was the validation of integration. The following questions needed to be resolved: Are we able to put these components together meaningfully? Do they work as expected? Then came the validation of optimization. In other words, are the resulting architectures the best ones for a future aircraft? Do they meet the project goals?
The first part involved tests by each partner, at the component level. The second part, integration, used a test rig at Hispano-Suiza’s facility near Paris. The last part, optimization, used a virtual iron bird.
“POA showed that we need to concentrate on integration,” Faleiro stated. This means understanding the management of electric loads and improving power electronics. Actual installation has to be assessed as well, Foch pointed out. Last, but not least, integration means solving thermal issues.
The U.S. Air Force Research Laboratory’s John Nairus has some assertions about thermal issues. First, do not create waste heat. If you do create it, make it hot, because it is easier to manage. Nairus’ third assertion is “do something useful with the waste heat.”
Rather than integration, the future will be process-oriented, Faleiro believes. In other words, integrating requirements across ATA chapters (which technically describe every function down to the component level). Both Faleiro and Foch insisted on the need for standardization. “Perspectives are great but the all-electric aircraft is still challenging,” Foch summarized.
Although Dassault last year made it clear that more electric technologies were so far not suitable for business aircraft, the manufacturer of the Falcon jets is now involved in MOET. “Our interest is in the all-electric airplane,” a company executive for advanced projects told AIN. According to him, the relatively small amount of power needed by flight-control actuators would make it easier to move directly to electro-mechanical actuators. Such EMAs have no hydraulic backup, unlike electro-hydrostatic actuators (EHAs). “We believe we would get a significant advantage in terms of maintenance, although there might be a weight problem,” the executive added. He insisted an exhaustive study still has to be conducted.
The POA project consortium is made of 46 partners. In its fifth framework program (FP5), the European Union partly funded the i99-million project ($124 million). The i70-million MOET project, starting this year and part of the FP6, will focus on electricity, rather than trying to make the best use of several power sources. The FP7’s Clean Sky project, in 2013, should take electric systems to flight test.
