Boeing 787 Dreamliner - Mark Wagner [53]
BRAKE-BY-WIRE
Just a month before the electric ice protection news broke, Boeing awarded contracts for another radical electrically based system, brake-by-wire. The 787 became the first ever commercial jetliner to have electric brakes in place of the conventional hydraulically actuated brakes. Two suppliers, Goodrich and Messier-Bugatti, were set up to compete for the digitally controlled system, which included the aircraft’s eight main wheels, electromechanically actuated carbon brakes, and the controlling electronics package.
Although potentially a risky development, electric brakes offered weight and efficiency savings, as well as fitting better with the company’s modular assembly plans. In particular, by helping dispense with the need for installation and test of hydraulic systems, Boeing believed electric brakes would save time during assembly and test.
Being digital, the system also offered operators the benefit of inherent monitoring and self-checking capabilities. Better reliability was expected because it had fewer parts than a similar hydraulic brake system. If something did break, its modular design meant specific parts could be replaced on the ramp without necessarily having to remove an entire brake assembly.
Although new to the jetliner world, brake-by-wire technology had been tested in the 1990s on a USAF-led program involving an F-16 test aircraft. Goodrich developed the first fully integrated electrically actuated brake system for later versions of Northrop Grumman’s RQ-4B Global Hawk unmanned air vehicle. For the 787, Goodrich’s Troy site in Ohio supplied wheels and brakes, with its actuation systems unit in Cedar Knolls, New Jersey, providing the electromechanical actuators (EMAs). These replaced the hydraulic pistons used to supply clamping loads to the aircraft’s brake discs. Goodrich’s fuel and utility systems unit developed control software.
Messier-Bugatti, in association with Sagem, developed a brake-by-wire system that the company believed marked “as much of a breakthrough for airlines as was the advent of carbon brakes some twenty years ago.” The Messier-Bugatti system involved a power supply, brake control, and the electric brake itself, all of which are connected to an electric brake actuation control (EBAC). The unit comprised an electric motor, reduction gear, ball screw and nut, and rotor and stator carbon discs, and converted electrical signals into commands and drove the brakes. Tests were performed at Villeurbanne, the center near Lyon, France, responsible for R&D and carbon disc production for aircraft as well as for Formula 1 racing cars.
GE Aerospace was responsible for the brake control and monitoring system, one of three main work packages under an integrated landing gear system contract awarded in 2004. The brake control was a wireless-based system that picked up wheel speed and pressure information, and combined it with rudder pedal, throttle positions, and other sensor data to instruct the brakes what to do. GE also developed the nose gear steering and landing gear actuation systems as well as high-lift actuation systems. Gear actuation was software-controlled rather than mechanically interlinked, reducing closing and opening times.
The landing gear actuation package included an emergency, 3,000 psi alternative deployment system. The high-lift actuation system powered, actuated, and monitored the flap and slat system and included power drive units, a transmission system, and rotary actuation and braking devices.
The nose and main landing gear were developed by Messier-Dowty, the win being its first prime contract with Boeing on a commercial program. The design was the first of its type to make extensive use of titanium and composite. The inner cylinder of the main landing gear was made from titanium, “and that’s a first,” said the company’s vice president, Grant Skinner. The main gear’s side and drag braces were made from