All-electric Falcon jet could be launched by ’15

 - July 27, 2009, 10:17 AM

Dassault Aviation could launch an all-electric Falcon business jet program in 2014 or 2015, said company engineers at a conference held by the ASTech Paris Region aerospace cluster at the Paris Air Show in June. According to Yvon Ollivier, a Dassault coordinator for advanced studies and ASTech’s president of the “on-board power” project, there are numerous benefits of replacing hydraulics with electric power, but some challenges remain for designers.

Current aircraft architectures rely on electric, hydraulic and pneumatic (air) power, but the latter two present a number of disadvantages. For example, “Current anti-/de-icing systems, such as that found on a Falcon 2000, use hot air and have
poor efficiency. They essentially warm up the outside air,” Ollivier said. Moreover, using bleed air from an engine reduces the engine’s efficiency.

In addition, leaking hydraulic fluids are flammable and harmful to the environment. As a result, even common maintenance operations become relatively complicated when hydraulic fluid has to be drained.

Making all aircraft systems electric is becoming more feasible, as recent progress in permanent magnets is enabling the construction of smaller, more reliable electric actuators.

Hoped-for benefits of an all-electric architecture are numerous. First, according to Jean-Claude Vannier, a professor at engineering school Supélec and ASTech’s vice president for the “on-board power” project, a homogeneous system is simpler. In the case of electricity, it is also more easily controlled.

In addition, a homogeneous electrical system simplifies aircraft manufacturing, because wires are easier to install than ducts and pipes, Ollivier pointed out. Finally, man-machine interfaces get simpler, too, as system synoptics are easier to draw.

System Simplicity

One way to make the aircraft simpler is to take advantage of the electric systems’ reversibility. For example, as Vannier pointed out, once the engine has started, the starter morphs into a generator. Even electro-mechanical actuators can be converted into generators when braking. The resulting power can be used to feed other motors.

Unifying on-board power allows engineers to downsize generators. In current-generation aircraft, each power generator (electric, hydraulic or pneumatic) must be sized for the maximum needs of the related systems. But these generators are never used at their peak power simultaneously. An all- electric system reduces the maximum power needed, allowing for smaller, lighter power generators.

On an all-electric Falcon, a fuel cell could replace the auxiliary power unit. With minimum bleed air, the engine could have a starter-generator mounted on a shaft.
Wing de-icing could be performed with electric heaters or electro-expulsion devices.

Depending on the power needed, components would be fed under different voltages. Low-power components would derive power from a 28-volt system, while 270 volts would supply high-power components, such as control surface actuators.

Business aircraft may well be the right size for early power-by-wire applications, such as for flight control surfaces. The power needed to move a Falcon’s rudder, for example, is on the order of 2 kW. An A380 needs 10 kW for its rudder. “The power required by electro-mechanical actuators is well suited to business aviation,” Ollivier said.

‘Snowball Effects’

As part of its research, Dassault has studied the “snowball effects” of going all-electric. For example, although the all-electric system is more efficient, if it is heavier or bulkier than the current system, it will require more space (creating more drag), while the extra weight will require more lift. The result is that the airplane will burn more fuel.

When electric systems replace hydraulic systems, such as brakes and flight-control surfaces on a Falcon 2000-size jet, the total installed power remains unchanged, at around 600 kW. The big step is with the move to an all-electric system, which would include the environmental control system. Total installed power required then drops to about 200 kW.

In terms of aircraft empty weight, however, the result is quite different. An aircraft with only its hydraulic systems replaced by electrical systems weighs approximately 400 pounds more than the same aircraft with hydraulic systems. But with an all-electric architecture in the aircraft, the additional weight jumps to a prohibitive 1,700 pounds. “Suppressing bleed air is workable only if we manage to get the electric environmental control system lighter,” Ollivier said.

Nevertheless, he expressed strong belief in a potential for improvement. “A bleedless engine can be optimized,” he asserted. In addition, high-power electronic components will become smaller and need less cooling.

Power management can be further optimized, too. Ollivier cited “smart shedding.” When moving the landing gear down, for instance, the environmental control system could be stopped.

Environmental Programs

Dassault is now completing theoretical studies that will end next month. Technology developments started in 2008 will last until 2012. Under the European Union’s Clean Sky joint technology initiative, a validation testbed will help engineers understand how “such an enormous electric network works,” said Ollivier.

As part of Clean Sky, Dassault co-leads (with the Fraunhofer Institute) the Eco-design integrated technology demonstrator. Completion of that demonstrator is planned for 2015, and Ollivier estimates that Dassault could launch an aircraft program that year, if not the year before. This estimate is consistent with the company’s stated aim of having in service by 2020 a Falcon that burns 40-percent less fuel than current-generation models.

A lot of work remains to be done before then, however. Engineers need to model the energy losses of electro-mechanical actuators, and develop better models of energy storage in supercapacitors.

Moreover, engineers need better models of the system in its entirety to see what effect an all-electric system has on other components. Among the possible effects are thermal interaction, possible electromagnetic interference or impact on engine performance.