Brake with tradition

A UK engineering team is hailing a civil aviation world first after equipping the next generation of Bombardier commercial jets with an all-electric braking system.

Dorset-based aerospace group Meggitt is aiming to replace all hydraulics in BombardierCSeries jets with the EBrake electric braking system, making them safer and easier to maintain.

Most modern aircraft use brake-by-wire systems, which use a transducer connected to the brake pedal. When a pilot steps on the pedal an electrical signal commands hydraulic pumps to produce pressure on each of the brakes.

However, no commercial aircraft combines brake-by-wire technology with electric brake actuation.

Engineers are refining the all-electric brake system of the Boeing 787 Dreamliner, which has yet to have its first flight.

Bombardier demonstrated its hydraulics-free technology on a Global Express test jet in the US last month. The aircraft was equipped with Meggitt’s EBrake and Messier-Dowty’s landing gear with electric brake wiring harnesses.

The test lasted for more than seven hours and included five landings and a series of high-speed braking exercises on the ground. While the initial results were successful, the aircraft is still being tested to validate the robustness and reliability of its design.

The Meggitt design includes four actuators installed on each of the jet’s four main wheels. Each actuator uses a DC motor to drive a ball screw and gear train. All 16 of the actuators are individually controlled and the force they generate is determined by how far the pilot presses the pedal.

Mark Walker, vice-president of engineering at Meggitt, said designing an electric brake actuation system for the jet was a challenge for his team of engineers.

’The brake environment is a hostile environment for an electric actuator,’ he said. ’There is a lot of vibration that is induced from the brakes and there are also relatively high temperatures from the brakes. We had to design the actuators so they are reliable enough to handle that.’

Another challenge, said Walker, was designing the system so that it was small and unobtrusive. ’Hydraulics are a great tool for packing a lot of power into a pretty small space,’ he said. ’It was a challenge to come up with an electric motor, gear train and a ball screw technology that occupies the same or a smaller amount of space.’

Also, the team has to design a way to control each individual actuator. ’The system that we developed has a load sensor in it so we’re using a force feedback signal to tell the control system how much force is coming out of each individual actuator,’ said Walker.

The civil aviation industry has been looking to move towards electric braking systems but the technology has only recently matured.

Walker said one reason for moving away from hydraulics is safety as fluid leakage presents a fire hazard around hot brakes. Hydraulics systems also have less redundancy built into them.

’With electric brakes there are multiple motors driving each brake and they all operate independently of one another,’ said Walker. ’So if you lost a motor you wouldn’t lose the other motors within that system.’

Doug Moseley, director of research and technology at Meggitt, said another element that makes the electric braking system attractive is its easy maintenance. ’A failed actuator can be changed without much interruption at all,’ he said. ’There is just an electrical connector to remove and a few bolts to remove.’

Moseley claimed this is much simpler than the maintenance on hydraulic equipment. ’With a hydraulic system you have to remove the hydraulic housing, which means you have to jack the aeroplane and take off the main wheel to remove the hydraulic component,’ he said. ’It takes a lot of time and effort.’

Moseley added that electric braking systems are also easier to install during the aircraft assembly process.

More importantly, electric braking is in line with the industry’s move towards more environmentally friendly aircraft that are fuel-efficient and use less toxic hydraulic fluids.

’The commercial field is poised to adapt electric brakes,’ said Moseley. ’They’re very modern and they have that “gee whiz” appeal to them.’

Siobhan Wagner