A contractor used micropumps for a backup hydraulic system and cut weight from a supersize aircraft.

With an overall length of 73 meters and a wingspan of nearly 80 meters, the Airbus A380 provides seating for 525 passengers and a range of 15,200 km (more than 9,400 miles)—sufficient to fly nonstop from New York to Hong Kong. To gain maximum fuel efficiency and payload capacity, designers found several ways to keep weight down. Composites and other lightweight materials account for more than 25 percent of its structure, and engineers scrutinized every aspect of the aircraft to keep weight down.

Of particular interest were heavy hydraulic lines running the length of the aircraft from large centralized pumps to equipment, such as brakes, landing gears, and the nose wheel steering system. Ordinarily, large commercial jets have three sets of redundant hydraulics—two primary circuits and a third backup for safety, all adding up to a hefty load of piping.

Engineers saved weight wherever possible to maximize payload capacity of the A380, the world’s largest passenger aircraft.

To reduce this bulk, the hydraulic backup circuit was replaced with a decentralized fluid-power generation system on the A380. In the backup system, signals from electronic control units activate several small, electrically driven pumps, each located close to the systems to be controlled. The micropumps provide 5,000 psi (350 bar) of local hydraulic pressure over short runs of small-diameter lightweight piping for braking and steering, so the power is always available in an emergency.

This Local Electrical Hydraulic Generation System was developed by Messier-Bugatti, a subsidiary of the SAFRAN Group.

Early Decisions

In optimizing system performance, the engineering team on the project faced major challenges in integrating and sizing the large number of components for the mechanical, electrical, and hydraulic systems. Moreover, they needed to assess risk factors such as electrical overheating.

Practical deadlines and budgetary constraints prohibited numerous physical tests of system mock-ups. Instead, work in designing and optimizing the performance of the system would have to be done early in the plane’s development—before any hardware was built and at the same time that the design of other aircraft systems was under way.

In addition to emergency braking on all 20 wheels
of the A380, the LEHGS also provides backup hydraulic
power for the all-important nose wheel steering system.

Messier-Bugatti’s engineers met the challenges by using multidomain simulation software from LMS International of Leuven, Belgium. The product is called LMS Imagine.Lab AMESim. Using a module known as Ground Loads, engineers began by selecting and piecing together individual components and subsystems from among a library of predefined validated components: hydraulic resistance, hydraulic component design, electromechanical, electric motors and drives, thermal resistance, thermal hydraulics, thermal, hydraulics, and electrical basics.

AMESim predictions of system performance matched bench tests of
actual system behavior.

The overall system model is created graphically in the software. Engineers are prompted to enter parameters where necessary, but are not required to write code. In this way, the software creates a multidomain system model from the overall conceptual information of interconnected parts and subsystems without requiring a full 3-D geometry representation, so engineers can simulate and predict the behavior of intelligent systems long before detailed CAD geometry becomes available.

According to Michael Benmoussa, senior design engineer on the project, “Simulation enabled us to anticipate and reduce the inherent development risks of a new technology by incorporating an upstream validation regarding the technical choices.”

Complex Behavior

The solution modeling and analysis capabilities of Ground Loads allowed the engineers to analyze the system’s hydraulic behavior in terms of performance, stability, and robustness. Engineers also used the model to study the thermal characteristics of the hydraulic circuit and to evaluate the need for heat exchangers. They used the results to establish the sizing, output, and other product specifications for the entire hydraulic power generation system, including the tank, pump, and accumulator.

Micropumps provide 5,000 psi of local hydraulic pressure
over short runs of small-diameter lightweight piping for
braking and steering—always available in an emergency.

Using a digital model, engineers were also able to explore a large set of parameters and scenarios. When developing a steering system, for example, various combinations of components (actuators, motors, valves, etc.) could be compared from specification to validation, thus significantly improving the steering system’s quality.

According to Benmoussa, Messier-Bugatti was able to tune the complex multiphysics systems without performing an extensive set of bench tests.

Simulation results were later confirmed in bench tests, Benmoussa said, but because they were informed with the results of the simulations, Messier-Bugatti’s engineers could size components accurately early in development. This significantly reduced the number of physical prototypes they would need to validate their design of the system.

This article was prepared by staff writers in collaboration with outside contributors.