21/dic/2009 17:34:58 Virgilio E. Conti Contatta l'autore

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Flight controls, a brandnew technology


Alitalia - Engineering and Maintenance Division

Technical training: draft issued by chief instructor Virgilio Conti

Fonts: Alitalia, Airbus Industrie, Boeing, NASA

Digital Fly By Wire

One hundred years after the Wright brothers, first powered flight, airplane designers are unshackled from the constraints that they lived with for the first seven decades of flight because of the emergence of digital fly-by-wire (DFBW) technology. Many technologies with significant advantages fail to catch on due to economic constraints, or sometimes simply because their time has not come. Fly-by-wire demonstrated that its time had come.

  • At its most basic level, fly-by-wire technology reduced the weight and maintenance costs of aircraft by replacing heavy mechanical systems with lightweight wires. But its real significance was its impact on aircraft design and performances capability.

  • Today, digital fly-by-wire (DFBW) systems are integral to the operation of a great many aircraft.

  • These systems provide numerous advantages over older mechanical arrangements. By replacing cables, linkages, push rods, pull rods, pulleys, and the like with electronic systems, digital fly-by-wire reduces weight, volume, the number of failure modes, friction, and maintenance.

  • It also enables designers to develop and pilots to fly radical new configurations that would be impossible without the digital technology.


Digital fly-by-wire aircraft can exhibit more precise and better maneuver control, greater combat survivability, and, for commercial airliners, a smoother ride.

New designers seek incredible maneuverability, survivability, efficiency, or special performance through configurations which rely on a DFBW system for stability and controllability (see appendix Airplane axis and stability). DFBW systems have contributed to major advances in human space flight, advanced fighters and bombers, and safe, modern civil transportation.

The story of digital fly-by-wire is a story of people, of successes, and of overcoming enormous obstacles and problems. The fundamental concept is relatively simple, but the realization of the concept in hardware and software safe enough for human use confronted the research-industry team with enormous challenges.

DFBW technology has demonstrated that was possible to build and integrate a combined hardware and software flight-control system, and that it had all the advantages expected of fly-by-wire with additional flexibility provided by embedding the flight-control laws in computer code. The world was apparently ready, and now the skies are filled with digital computers flying "in very tight formation."

The Airbus A-320 has a high level of success with its control system, which features a unique architecture to enhance reliability. The Airbus flight control system has migrated to all new models of that firm's aircraft. Even the conservative industry, Boeing, has launched the B-777 with a digital control system of more conventional design.



History of Flight-Control Technology

Flight controls philosophies had progressed through several stages of emphasis on inherent and dynamic stability to instability. Flight control technology initially had limited mechanical means and a great dependence on the pilot. By 1960, control of both unpiloted missiles and automatic control of piloted aircraft greatly reduced this reliance. A technology called "fly-by-wire" - due to its electrical, rather than mechanical, nature - made these accomplishments possible.





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