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Mon, Oct 10, 2005

Electric Brakes Offer Advantages

Boeing 787 One of First to Benefit

The Goodrich brake unit for a Boeing 787 Dreamliner looks like any other jet brake pack -- until you start looking for a place to connect the hydraulic line. You can look as long as you like, but there isn't one: the brake is electric.

Goodrich is one of two vendors whose brakes are available on the Dreamliner; customers may opt for Messier-Bugatti brakes instead. But either way, they'll be getting something new in airliners: electric brakes.

In an electric brake, the toe brakes in the cockpit actuate a pedal position and/or pressure controller, whose input feeds into the master brake control, which sends a signal to the brake pack, where electromechanical actuators (EAs) move the pads into contact with the discs, turning energy into heat by means of friction, and slowing the airplane.

So at a glance, the system simply substitutes electrical components for the familiar master and slave cylinders used in a hydraulic brake system. But not so fast, there, throttle jockey: that does not take into account the advantages of electric brakes.

Writing in SAE's Aerospace Engineering magazine (Aero-News: we read this stuff so you don't have to), Goodrich's Leibert Danielson enumerated the advantages of electric brakes, many of which come about because of the high reliability, consistency and modularity of modern electronics: reduced aircraft assembly time for the manufacturer, improved reliability and reduced maintenance for the operator, higher system redundancy for both reliability and safety. "An added benefit is the elimination of brake fluid, with its leaks and fire hazards," he writes.

The greatest benefit, as Danielson says, is that "digital control sets up an infrastructure for information gathering, health monitoring, and action..." or in other words, an intelligent braking system.

Imagine a braking system that "knows" how hard to slow the plane to make the taxiway turn-off, because it's wired into the same electronic brain that sees the GPS and the airport diagram in memory. Such a system would never over-brake and risk fire or brake damage. Pads and rotors would last longer. It could even be wired in with the autothrottles and thrust reversers -- taking the variable (pilot skill) out of the equation and ensuring a best-case in a stopping emergency, as well as optimum deceleration in normal cases.

No more dirty looks from the purser because you braked a little, er, more abruptly than the conditions actually required -- on the "better safe than sorry" approach that humans must take.

Heck, the brake brain could even compare brake action and wheel rotation with what accelerometers and velocity sensors are telling it, and then report braking action to the crew, or even directly to the airport. How many times have you listened to PIREPs of braking action and tried to figure out how the results that a guy you don't know in a type you're unfamiliar with compare to your own ride?

So the beauty of electric brakes is not just in the concrete ways in which they are better at doing what we do now -- but in the ways in which they make it possible to do things that we have never done before. This is reminiscent of the way that electronic fuel injection began as a more reliable replacement for a temperamental (and heavy) mechanical system, and grew into a new generation of engine control.

The Goodrich electronic braking system fulfills this promise already in certain ways, for instance by incorporating a continuous self-test system, and by providing extra electromechanical actuators on the brake pack to provide greater redundancy and reduce the consequences of an actuator failure. Of course, this sounds like something that would be a good fit with UAVs, and -- no surprise -- it is. Goodrich's system is already being fitted in the RQ-4B Global Hawk ISR (intelligence, surveillance, reconnaissance) plane. The electric brakes will be field tested in the coming year.

Electric brakes are not radically new -- inventor Victor Ochoa got a patent on them in 1907 (for railroad use -- see drawing, above). Indeed, they're common on light trailers -- such as the ones that ultralight, trike, glider and gyro pilots use to haul their machines. The first airplane flown with electric brakes was an F-16 flown at Edwards Air Force Base in 1999.

Will electric brakes be coming into GA? The answer is a qualified yes. It's easy to imagine forward-looking Eclipse, whose Eclipse 500 already is a model of computer integration, adopting electric brakes. One suspects that, if the technology had been ready when the first-generation Eclipse was coming together, it would already have been there -- but that plane has quite enough firsts as it is.

The lighter end of the market is another question. Usually, these days, innovations percolate up through the experimental market, in part because the FAA has erected this Alpine certification barrier against new technology, crowding out any innovator who hasn't got a desk at a major aerospace prime contractor. But then, that's what they said about glass panels, too, and glass panel giants Avidyne and Chelton began by serving up non-TSO'd units to experimental users. (Chelton still sells an experimental version of their unit, which lets them try out advanced technology before they leap the certification Matterhorn).

But the technology that Goodrich and Messier-Bugatti are using is not astrophysics, and some of the componentry may already exist. Still, it will be a long time before light experimentals have electric brakes (except on their trailers!) and longer still before they are a feature of certified single-engine lightplanes.

FMI: www.wheelsandbrakes.goodrich.com


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