Eurocopter considers FBW for civil helos

 - July 2, 2007, 9:21 AM

Eurocopter is investigating all-electric helicopter system architectures, including flight controls, with the goal of having them in service within 10 years. The Marignane, France-based manufacturer clearly intends to substitute electricity for current sources of energy for systems, such as hydraulics. The change is likely to result in lower maintenance costs and improved handling qualities.

Currently the only helicopter with fly-by-wire controls is the Eurocopter/ Agusta/Fokker NH90 military transport. But it has hydraulic actuators, with local hydraulic power generation. What Eurocopter is considering is a helicopter with all-electric flight controls.

Marc Gazzino, Eurocopter’s head of electric system studies, suggested to AIN that validating the reliability of such a system will be expensive. He also said that the business case for introducing such a system calls for starting with medium
to heavy helicopters. “However, there is no consensus in the helicopter industry and some would rather begin with light rotorcraft,” he added.

The company will take a two-pronged approach to reliability testing, Gazzino explained. Initial analysis will be performed with the aid of computers. Second, hardware will be ground tested in failure modes that are more demanding than would arise in normal operations. “We will work out an equivalent to a normal lifecycle,” Gazzino said.

Fly-by-wire is already well established in fixed-wing aircraft such as the Airbus A320/330/340/380, Boeing 777 and Dassault Falcon 7X. Fly-by-wire gives the pilot better function integration, Gazzino said, allowing the autopilot to work more closely with the controls. Such controls also offer improved handling qualities and more precise flying, which means a smoother ride for passengers, said Philippe Antomarchi, a researcher at Eurocopter’s design office.

Another benefit of fly-by-wire is the simplification of maintenance. The scheduled checks that come with hydraulics are eliminated. “The system monitors itself continuously and can anticipate potential problems, so maintenance is on condition,” Gazzino told AIN.

Perhaps surprisingly, Eurocopter researchers do not see reducing the acquisition cost of such a fly-by-wire system as the main challenge. As recently as 2005, Fabrice Brégier, then CEO of Eurocopter, cited acquisition costs as the reason the company had “no particular plan” for fly-by-wire controls for civil helicopters.

There are still a number of technologies to validate. Although Eurocopter is requesting that equipment makers collaborate closely from the outset, the business case for such participation by suppliers is not as good as it would be in the airplane industry because helicopter production volumes are smaller, noted Antomarchi.

In addition, implementing electric systems on helicopters is more complicated than on airplanes. “Redundancy cannot solve as many reliability issues, so system reliability is even more critical,” he said. Nevertheless, Eurocopter could find some common ground with Dassault, Alenia and Saab in business and regional jets.

All participate in the More Open Electric Technologies research program, funded by the European Commission. Although the program meets mainly Airbus’s needs, manufacturers of smaller aircraft have found areas of common interest. This holds the promise for bigger production volumes for some components and therefore a better business case for equipment suppliers.

Gazzino sees protection of the environment as one of the main drivers behind the interest in replacing hydraulic systems with electric ones. The environmental impact of electric power over its life cycle is far lower than that of hydraulics– mainly because of the fluid. Landing-gear actuators and hoists, for example, can go electric. “Electric hoists already perform better than hydraulic ones on the EC 145,” Gazzino noted.

Antomarchi said that eliminating only one hydraulic system might not justify the investment. However, a completely new electric system architecture on the aircraft, with optimized power management, will likely make a more compelling case.
Moreover, from a maintenance perspective, there is little point in eliminating one hydraulic system and retaining others. Helicopter designers will therefore likely wait until they can go all electric.

Regardless of the elegance of eliminating hydraulics, demand for electric power is increasing. In the 1970s, there was 30 kilowatts available on a Puma. Today’s EC 225 Super Puma offers 120 kilowatts.

There is also an increasing need for mission equipment such as searchlights. Moreover, airframe anti-icing and cabin air conditioning are power-hungry. On a Super Puma, more than one-third of the available electric power goes to these two systems–when active.

Improvements Needed
Eurocopter researchers are endeavoring to counter the trend toward bulkier and heavier generators. Gazzino, Antomarchi and their colleagues are thus working on increasing the voltage. For a given power, this allows a lower amperage and therefore smaller-section wires and reduced weight. Designers are targeting a voltage of 270 volts, almost 10 times the current 28 volts.

Simultaneously, today’s generator rotation speed of 12,000 rpm is to be increased. “We are talking about twice or four times this,” Gazzino said.

Finally, they are trying to increase the temperatures tolerated by components. “What limits the amperage is the temperature the wire and its isolator can accept,” Gazzino said. Heat is produced in a wire because of its resistance. The amount of heat varies with the square of the amperage. Again, weight can be saved by reducing the wire’s section, provided the resulting smaller surface of isolator can withstand the heat.

It is important to find more heat-resistant isolators to keep weight in check. Without an appropriate isolator, design engineers could find themselves adding cooling systems. “In coils, our target is 300 degrees C, rather than the present 150 degrees,” Gazzino said. In electronic components, Eurocopter is aiming at 150 degrees, instead of 70 to 80.

Another limiting factor is the use of air as an isolator. In laying out electric systems, designers use the air surrounding components as an isolator. However, as the helicopter climbs, the air gets thinner. Therefore, designers have to take into account the air’s rarefaction if they want to avoid arcing at altitude. This can limit voltages.
Eurocopter engineers are also working on new batteries. For environmental reasons, they plan to replace nickel-cadmium with lithium-ion. “Within two years, we hope to enhance the power-to-weight ratio by 30 percent,” Gazzino told AIN. Keeping those batteries affordable is the main challenge.