Messier-Bugatti readies 787’s all-electric brakes

 - July 7, 2008, 10:08 AM

Messier-Bugatti (Hall 4 Stand B12) is looking forward to seeing its all-electric braking system on the Boeing 787 when it makes its first flight in the fourth quarter of this year. According to François Tarel, the Safran group subsidiary’s vice president for wheels and brakes, the system received its “safety of flight” approval from Boeing last November, following a series of bench tests. The company currently is flight-testing a slightly different system on an Airbus A340-600 test aircraft.

For the 787, endurance testing is under way to monitor performance and costs. In parallel, Messier-Bugatti is working with Boeing on the aircraft’s certification. “We have delivered two complete systems for flight-test aircraft,” said Tarel.

Messier-Bugatti bases most of its electric brake design engineers at its headquarters in Vélizy, near Paris, and production occurs at Molsheim in eastern France. The company also has a small team in Seattle, where “they work with Boeing on day-to-day issues, especially integration,” Tarel explained.

Integration is more important with brake-by-wire than it is with conventional brakes. For example, the electric braking actuating controller (EBAC) has to be interfaced with the anti-skid system (which is supplied by Crane Hydro-Aire). In addition, brakes must be able to work with the power available, and electromagnetic compatibility must be verified.

The EBAC drives electric braking. It is linked to motors that convert electrical power into a rotation movement. These motors drive gear wheels, which in turn drive a ball screw and nut. The screw is linked to the piston that presses the carbon disks together. The piston is no longer hydraulic.

Tarel identified several features that are unique to the Messier-Bugatti system. “For example, when the EBAC sends an order to the actuators, they exert pressure depending on what the anti-skid system allows,” he explained. “To get feedbackabout the actual load on the carbon disks, we do not need
to use any load sensor. We rely on measuring the actuators’ position.” This reduces weight and improves performance, he said.

Another advantage can be found in how the brakes are maintained. On the actuator, the piston and the motor can be removed separately. Finally, Messier-Bugatti’s system uses the Anoxy 66 oxidation protection coating on the carbon disks, which further improves durability.

Asked about the impact of 787 program delays on Messier-Bugatti’s production plans, Tarel said the company is busy with other programs such as the Airbus A320 and the 737. The delay on the 787, he said, actually gives the company the opportunity to ensure its brakes will be more mature at entry into service.

The company now is focusing its product support planning on the Sagem-made EBAC unit. Messier-Bugatti has support facilities in Seattle, Singapore and Vélizy. It also continues research and development of brake-by-wire technology, having tested on an A340-600 a new demonstrator that features a slightly different control process.
Electric braking is undoubtedly lighter than a conventional hydraulic system, but the brake-by-wire systems offer other benefits, including with regard to maintenance. “First, brake wear is closely monitored, landing after landing,” Tarel explained.
Second, whereas a leaking hydraulic system requires immediate maintenance, its electric equivalent will be acceptable for flight dispatch in most circumstances because the multiple actuators provide adequate redundancy. Third, failure diagnosis is made more quickly because it is easier to find the failed component than the location of a leak.

On the 787, Messier-Bugatti is competing with Goodrich, which also offers electric braking. According to Tarel, of sixteen 787 customer airlines that have chosen a brake supplier, seven have opted for the French technology. Launch customer All Nippon Airways of Japan has picked the Goodrich system. The 787’s main rival, the Airbus A350, will be equipped with hydraulic brakes.