Aircraft go electric

9/21/2003

Just as consumers once harkened to the utility industry slogans — “Live Better Electrically” and the “All Electric Home” — engineers are embracing “Fly Better Electrically” and the “More-Electric Airplane” in the design of aircraft.

The electrifying idea, originated years ago by Pentagon researchers, is leading toward one of the biggest updates in military and commercial aircraft technology since the Wright Brothers.

It involves using electricity to power aircraft systems traditionally run with hydraulic, pneumatic, and mechanical devices. Pilots rely on these heavy, difficult-to-maintain, industrial-age systems for everything from starting a jet's engine to steering during flight to hitting the brakes at touchdown.

A commercial airliner's hydraulic system may include miles of high-pressure tubes and pipes running nose-to-tail and wingtip-to-wingtip. They're filled with hydraulic fluid; leak if fittings or seals fail; and involve fluid reservoirs, filters, valves, and other parts.

In a military combat aircraft, those systems mean more than extra weight, lost fuel economy, and expensive maintenance. They spell vulnerability to enemy fire. A few lucky shots from a foot soldier can down a plane by severing key hydraulic lines.

The MEA program enlisted Air Force, the Navy, NASA, the Defense Advanced Projects Agency, and private industry. Efforts paid off handsomely, according to interviews with key individuals in the program.

“A great deal has been achieved,” Dr. Richard T. Fingers said. He is deputy director for technology in the propulsion directorate at the Air Force Research Laboratory at Wright Patterson Air Force Base in Dayton. The lab, which has a key role in the effort, does $2.5 billion of research annually for the Air Force and other customers.

MEA technology is moving into the designs of the world's most advanced aircraft. Other industries also are eyeing it. Automakers, for instance, view electric systems as a possible replacement for traditional brakes.

The Pentagon is investing billions in the first more-electric jetfighter.

It's the new Joint Strike Fighter, or F-35. Lockheed-Martin is developing and building the advanced, stealth-based warplane, which will replace existing planes like the F-16 and A-10 used by the Air Force, Marines, and Navy.

And the F-35 is just a step toward the military's ultimate target: An “all-electric” aircraft.

“The goal of the visionary All-Electric Aircraft concept of the future is to eliminate as many hydraulic power sources and hydraulic lines as possible,” Michael Yates, an engineer with TRW Aeronautical Systems, said in a report in a defense industry journal.

An “all-electric” airplane would still rely on a fuel-burning jet engine for thrust. But most other systems would be electric. Even the engine would change when the aircraft sheds hydraulic and pneumatic systems.

“The engine, which is currently required to produce thrust, pneumatic power, hydraulic power, and electric power, can now be redesigned and optimized to produce thrust and predominately electric power,” Mr. Yates explained.

Joseph Weimer, chief of electric technology at the Air Force lab, estimated that the needed technologies may be ready by 2010. Meanwhile, the MEA will bridge two eras in aircraft technology as planes shed some of the traditional pneumatic and hydraulic systems for lighter, simpler, electric and electronic replacements.

Commercial aircraft makers also are embracing MEA technology.

Airbus Industries' new A380 super-jumbo jet will be the first commercial jetliner bearing the MEA logo. The European consortium of French, German, Spanish, and United Kingdom aircraft companies hopes passengers will be flying in A380s by 2006.

Early in the A380's design, engineers realized that a plane so gigantic would be impossible without MEA technology.

The A380 will be the biggest commercial airliner ever built. Placed in the University of Toldeo's Glass Bowl, an A380 would stretch almost from goal line to goal line, with wing tips reaching beyond the sidelines. In the baseline configuration, it will carry 555 passengers. “Stretch” and other versions will hold almost 1,000. A Boeing 747-400 jumbo carries about 416 passengers.

Airbus claims the A380 will change the sociology of air travel. With lower fuel costs per mile, tickets will be cheaper, opening air travel to more people. The company promises “an unparalleled level of passenger comfort,” with wider seats, aisles, and open spaces for passengers to stretch their legs.

Passengers can thank weight-saving MEA technology for some of those amenities.

Consider MEA's impact on steering, which pilots do with moveable “control surfaces” like the “flaps” in the wing and vertical and horizontal stabilizers in the tail. Hydraulic systems move those surfaces.

All hydraulic systems magnify and transfer force through a fluid. Pneumatic systems use air. Hit the brake pedal on a car, and a piston telegraphs the force through brake fluid (a hydraulic fluid); the master cylinder with its pistons and valves; and brake lines — hydraulic tubes which carry fluid to the wheels. Pressure in the fluid pushes another piston in the wheel, which moves the brake shoes or brake pads so they press against the spinning wheel and stop the car.

MEA technology, in contrast, moves flight control surfaces with an electric signal traveling over wires.

Both the F-35 and the A380 will use hybrid electric-hydraulic devices termed electrohydrostatic (EHA). These self-contained units, located right where movement is needed, use a small electric motor to power a hydraulic piston. They have their own small reservoir of hydraulic fluid with no connection to any central hydraulic system.

Since EHAs get commands electrically over a wire from the cockpit rather than through a hydraulic line, the approach sometimes is termed “power-by-wire.” Wire, of course, is lighter than hydraulic lines, doesn't need fluid, valves, filters to remove contaminants, and doesn't leak.

EHA units are easier to maintain.

With only mechanical and electrical connections to the aircraft, they can be removed easily for repair or replacement. Removing hydraulic units requires draining hydraulic fluids, reconnecting fittings, refilling the system with fluids, “bleeding” to remove trapped air, checking for leaks in fittings, and other steps.

Airbus officials chose the EHA alternative when engineers presented plans for the A380's hydraulic systems.

The plane will use three systems for flight controls. Because of its size, the super-jumbo will have more flight control surfaces, and bigger surfaces. Moving those surfaces with conventional hydraulics would have added too much weight, with each pound reducing an airline's profitable payload of passengers and freight.

Almost a decade of research and testing led Airbus to adopt MEA technology to control the A380's weight, according to Michael Comes, director of engineering systems for the plane. Airbus will use EHA technology as a backup for hydraulic flight controls, which engineers are reluctant to completely discard. Hydraulic power is tried and true, used for generations and proven reliable in billions of hours of flight.

MEA technology, however, has its own track record aside from the recent research-and-development effort. It was used successfully in the Royal Air Force's renowned Vulcan bomber, the delta-winged craft that flew from 1957-84, including a stint in the Falkland Islands dispute.

Airbus estimates that MEA technology will reduce the A380's weight by about 3,300 pounds, a huge savings that means additional ticket sales for each flight. MEA technology will help make the A380 about 20 per cent more fuel-efficient than its smaller rival, the Boeing 747.

Safety gets a boost, Mr. Comes noted, since a total loss of hydraulic power in the plane would still leave the EHA controls operational.

The F-35 will use EHA controls, although Dr. Fingers and several other officials were reluctant to discuss details. Increased survivability apparently is one reason. EHA units are self contained and remotely located, eliminating the spider web of vulnerable hydraulic lines running through the plane.

Reduced weight, maintenance, and ground support are among the others.

When two dozen F-16 fighter planes are deployed, for instance, it takes 16 C-141 cargo planes to haul pneumatic gear needed to start their engines, hydraulic fluid servicing devices, and other support equipment. MEA technology could reduce that by 20 percent.

A host of other military and commercial aircraft systems are destined for electrification, including gearboxes and mechanically powered devices like fuel pumps, Mr. Weimer said.