Eaton Rolls Out 5,000-psi Aircraft Hydraulics

Jackson, MS-Following nearly four years of intense research and design effort, Eaton Aerospace (www.aerospace.eaton.com) is rolling out a new 5,000-psi hydraulic pump this month that could serve as the trailblazer for a new breed of high-pressure commercial aerospace parts.

The rollout, which took place here in May, marked the official transition of commercial aircraft industry from its venerable 3,000-psi designs to a new era of higher pressures. Many industry observers believe that other 5,000-psi commercial efforts will follow, possibly setting the stage for a move to even higher pressures in the distant future. "We've heard talk of engineers wanting to go as high as 8,000 psi eventually, because of the efficiencies it brings," said Eaton Aerospace Spokesman Peter Parsons.

Eaton's new 5,000-psi pump, designed for the Airbus A380, the world's largest airliner scheduled for introduction in 2006, takes the aircraft industry as far as it dares go for now, however. By making the long-discussed transition, Eaton's new pump serves as a demonstration of the engineering hurdles that await other OEMs and suppliers that will inevitably follow.

"The big challenges were life and cost," notes Phil Galloway, engineering manager for Eaton's Vickers Fluid Systems facility. "We had done 5,000-psi designs for the military since 1985, but military pumps don't have to last as long. Also, cost isn't a big concern for them."

Indeed, Eaton's new pump had to be designed to last about 40,000 hours, which translates to a life of about 20 years, and cost was a big consideration. "When you go to 5,000 psi, the design requires a lot of qualities that drive up the cost," Galloway adds.

Block Diagram

One such issue was the design of the pump's block. To boost longevity, Eaton engineers concluded that solid bronze or solid ductile iron blocks, which are relatively inexpensive and easy to manufacture, would no longer suffice. They found they could resolve the challenge by employing steel instead. "When you go to 5,000 psi, fatigue life of the material becomes a limiting factor," Galloway says. "The only way around that is to go with a material like steel, which has a higher fatigue life."

That, however, raised other issues, Galloway notes. Because steel doesn't provide an ideal bearing surface for the pump's pistons, engineers needed to employ bronze sleeves in the pump's block. That, in turn, boosted costs, and Eaton engineers say they are still examining alternative "sleeving" processes that employ molten bronze as a means of reigning in costs.

Airbus also added another wrinkle to the pump design when its engineers decided that they wanted the option of disengaging any of the aircraft's eight hydraulic pumps if problems surfaced. Airbus engineers made the decision mainly as a means of eliminating aircraft downtime, but because such measures were unprecedented, they raised another challenge for Eaton. Its engineers responded by increasing the size of the 27-kg pump so that it could accommodate a clutch. The clutch allows the pump to be disengaged in the event it becomes contaminated or fails for any reason.

To bring the pump to life, the Eaton team also embarked on a study of the best ways to accommodate commercial-type hydraulic fluids. Unlike pumps for military applications, which typically use synthetic or mineral-based fluids, commercial pumps often employ phosphate-ester-based fluids, which have different design requirements.

To accommodate commercial fluids, Eaton engineers spent several hundred hours studying the performance of the pump, then called for changes in pump timing and in the balance of its piston shoes. "Fluid properties play an important role in the equations that govern pump timing and shoe balance," Galloway says. "When you change the fluid, you have to make those modifications, or it will affect the behavior of the pump."

Pressure Up, Weight Down

By moving to 5,000 psi, Airbus engineers hope to reduce the weight of on-board hydraulic components. As pressure rises, they say, engineers can cut the size of hoses, fittings, clamps, tubing, and even actuators. By some estimates, the A380's move to 5,000 psi may cut on-board mass by as much as a metric ton.

Although Eaton is initially shipping just 24 pumps, plans are for the Jackson, MS facility to crank out thousands of the units, each of which will be priced between $15,000 and $20,000. According to news reports, Airbus has inked orders for approximately 90 of the 555-seat A380s to date. Ultimately, however, 100 to 200 more are hoped for.

Industry observers believe that if the 5,000-psi pumps fare well, more aircraft builders will follow Airbus's lead. "The aviation industry tends to be very conservative about pushing the envelope," Galloway concludes. "But in this case, the military has already paved the way for this technology."