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Introducing full FBW for business aviation 公务航空电传系统

时间:2011-12-01 09:18来源:蓝天飞行翻译 作者:公务机

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AVIONICS

Introducing full FBW for business av

Safety and economy spur drive to high-tech flightdeck.

Illustrations and photos courtesy Dassault
By Don Witt
ATP/CFII. Boeing 737, 757,
Airbus A320, Learjet series.

When Dassault’s Falcon 7X takes wing—an event due to take place in the first quarter of 2005—it will be a full fly-by-wire (FBW) aircraft.
FBW has been used for decades in military aircraft—in fact, Das-sault’s own Mirage 2000 flew back in 1978 with full FBW. In the civil-ian world, however, only the Airbus A320/330/340 series and the Boeing 777 are FBW. The A319CJ is marketed as a bizjet, but clearly it’s an airliner with modifications. Dassault’s Falcon 7X will be the first FBW business jet.

FBW’s genesis
Airplanes first flew with mechani-cal controls, and some of today’s turbojets still use them. Heavier, faster aircraft encounter Mach effects and require hydraulic actua-tion of controls. Since cables or push/pull tubes mechanically move the selector valves of the hydraulic control actuators, there is still a direct correspondence between the position of the control yoke and the position of the control surfaces.
It was air combat that forced the next step. Initially, the military

Dassault’s Falcon 7X, with full FBW flight controls, is due to fly in the first quarter of 2005.
became interested in FBW for its potential to improve the chances of aircraft surviving small arms fire damage.
There were other advantages. Turn rate is crucial in a dog fight. The tightest turn can be generated when both the wing and stabilizer are lifting together—but this places the center of gravity well aft, pro-ducing an unstable aircraft that a human pilot cannot control.
Computers, though, are able not only to control the aircraft while it’s in an unstable condition—they also relieve the pilot of worry about a high-speed stall and allow him to concentrate on the enemy. All in all, a perfect argument for FBW.
FBW debuted on fighters like the McDonnell F4 Phantom and early Mirages which had traditional con-trol systems (mechanically-control-led hydraulic actuators) augmented by computer feedback in stability augmentation systems (SAS).
SAS had limited-authority (about 5%) servos linked in series with the pilot’s controls. The aircraft could be flown and landed with a total failure of the SAS, though they’d fly more like drunken cows than their usual tightly-wound selves.
Ultimately, mechanical connec-tions and backups were dispensed with and full FBW fighters like the Mirage 2000 and the F16 emerged. Now the pilot’s sidestick sent sig-nals electronically to a flight com-puter (FC), which “knew” what was happening from its own sources of air data (pitot/static and angle of attack from the ADCs) and aircraft motion (from the IRSs.) The “control laws” in its program decided what to do with the controls, and sig-naled hydraulic control actuators electrically. Sensor feedback loops supplied info on how the controls responded. There was no direct mechanical connection between control surfaces and the pilot, who never actually knew what the con-trol surfaces were doing.
 
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