OEMs embrace more-electric aircraft systems

 - August 27, 2010, 6:07 AM

Business jet manufacturers are quietly progressing toward more-electric architectures, where electricity replaces hydraulic and pneumatic power in systems such as brakes, landing gear or even control-surface actuation. This avoids the use of environmentally unfriendly hydraulic fluids and ultimately should help reduce fuel burn.

The use of hydraulics has several disadvantages. First, hydraulic fluids sometimes leak, a negative for an industry looking to improve its perceived environmental impact. In addition, hydraulic fluids complicate maintenance and are difficult to recycle.

At the same time electric technology has improved rapidly in recent years. For example, motors have become smaller and can be integrated more easily.
As a result, this technology holds the promise of becoming competitive with traditional hydraulics in terms of power-to-weight ratio. An electric system is not necessarily going to be lighter than its hydraulic equivalent. However, once all the systems are integrated, it is likely that weight savings can be achieved at the aircraft level. This, in turn, will translate into lower fuel burn.

As a result of the interest in more-electric architectures Dassault is coordinating, with the Fraunhofer Institute, a U37 million ($48 million) European research project called EcoDesign-Systems as part of the Clean Sky program.

More-electric Systems
Which systems look easiest to electrify? “We are a system architect and we look at the big picture, not at how easy or difficult a system is to electrify,” Philippe Rostand, Dassault’s head of future Falcon programs, told AIN. He is hoping for greater energy efficiency at the aircraft level.

Electric systems are more flexible. This is especially true if there is a single source of power rather than a combination of  electricity, hydraulics and so on. For example, with an electric system, pressurization can be interrupted to extend the landing gear. Such “smart shedding” means that generators do not have to be oversized, producing a more efficient architecture.

The power available today on electro-mechanical actuators is suitable for business aircraft, although it is not sufficient to move the control surfaces of a large airliner. Nevertheless, business aircraft may not become “all electric” in one shot. “We are doing a lot of iterations,” Rostand said. Dassault engineers are studying all-electric configurations. They are also evaluating the merits of combined electric-hydraulic configurations, with and without taking bleed air from the engines.

“Some of our actuators are electric already in secondary flight controls,” Rostand pointed out. Spoilers, for example, are already electric and primary flight-control surfaces (such as ailerons) will follow.

Gulfstream is already using electric backup hydraulic actuators (EBHAs) as the third source of power for the G650’s control system. An EBHA features a self-contained reservoir and an electric pump backup mode that allows it to operate even after a loss of aircraft-supplied hydraulic fluid.

The EBHAs have yielded a weight benefit for Gulfstream. Moreover, the parts count is reduced, since an EBHA combines hydraulic with electric power to move a single actuating piston. Dissimilar actuation (between the main and backup systems) also has safety benefits, and the G650 will use less hydraulic fluid than it would with hydraulics alone.

Incorporating the EBHAs is possible because motor pumps are smaller and batteries can now handle regenerative voltage from electric motors, a Gulfstream spokesman said.

Gulfstream has encountered several challenges with this project. The first has been attaching electric motors to wing spars. Another challenge has been performance at high rates and loads. Finally, system reliability has to be thoroughly proven due to the use of more electronics.

Other manufacturers have also demonstrated an interest in more-electric technologies. Bombardier tested electric brakes on the Global 5000 in 2008. The trials have not yielded a business jet application yet, but Bombardier will fit an electric braking system to its C Series jetliner.

Hawker Beechcraft uses electric actuators on the Hawker 4000 for pitch trim and speed brake control surfaces. The rudder power control unit is a dual electro-hydraulic unit, which is lighter than a fully hydraulic unit, according to the airframer.