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`Fly by wire' jets

Regarding the economy-page article ``Boeing Hails Technology and Teamwork as It Rolls Out Jetliner,'' April 8: ``Fly by wire'' (f.b.w.) means something quite different to jet fighter designers and to commercial jet designers. The article states that in ``Boeing's first fly-by-wire jet ... mechanical connections from cockpit to rudders and wing flaps are replaced by electrical connections.'' Actually the connections to rudder, elevators, and ailerons, not to flaps, are electrical, allowing significant weight savings. Connections to flaps and other high-lift devices remain mechanical in the form of push-pull cables. Since the primary control is electrical, Boeing, Airbus, and others refer to it as f.b.w.

The f.b.w. concept, used in the primary controls of jet fighters since its introduction in the F-16, involves far more than mechanical cable replacement inasmuch as, with sensors and computers, it provides artificial stability to the inherently unstable aircraft. The advantage is that an unstable fighter is much more maneuverable than it would be if it possessed inherent stability. But entrusting the stability of a commercial jet to black boxes is a philosophy of design not needed or likely to be proposed.

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The highly publicized f.b.w. systems of jet fighters are not what commercial jet salesmen are talking about. Bernard M. Leadon, Gainesville, Fla.

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