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Fly-by-wire

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Fly-by-wire (FBW) is an advanced flight control system used in modern aircraft. It replaces traditional manual controls with an electronic interface. In older aircraft, pilots moved parts using heavy mechanical cables and pulleys. These mechanical or hydro-mechanical systems were quite heavy. They required complex routing through the airframe using cranks and hydraulic pipes. FBW technology uses electronic signals instead of these heavy physical connections. This change makes the aircraft much lighter and more efficient to fly.

Airbus-319-cockpit
Airbus-319-cockpit

The mechanism of fly-by-wire relies on a process called closed-loop feedback control. It begins when a pilot moves a control column or a sidestick. This movement represents a desired outcome, such as pitching the nose up. The flight control computer receives this input and calculates the necessary movements. It determines how to adjust various control surfaces like the rudder, elevator, or ailerons. The computer then sends commands to electronic controllers at each surface. These controllers use actuators to move the surfaces to the exact position required.

Feedback loop with descriptions
Feedback loop with descriptions

Sensors, such as LVDTs, then measure the surface position. This data is sent back to the computer to complete the loop.

There are different types of fly-by-wire implementations. Some systems are purely electronic, while others include mechanical or hydraulic backups. High-performance aircraft are often called Control-Configured Vehicles (CCVs). These aircraft may be designed with low or even negative natural stability. In these cases, the rapid-reacting FBW controls are necessary to keep the plane stable. Other systems use analog electronic controllers. The Concorde was the first production airliner to use an analog fly-by-wire system. Analog systems must use electronic devices to simulate the "feel" of the controls for the pilot.

Modern digital fly-by-wire systems offer much more than just movement. They include automatic stability systems that work without pilot input. Sensors like gyroscopes and accelerometers monitor the aircraft's rotation on the pitch, roll, and yaw axes. If the sensors detect unwanted movement, the computer automatically adjusts the actuators to stabilize the plane. Digital systems can also process data from many sensors at once. This includes inputs from altimeters and pitot tubes. This integration allows the computer to interpret the aircraft's environment in real time.

The history of this technology spans many decades of experimentation. Researchers first tested servo-electrically operated surfaces on a Soviet Tupolev ANT-20 in the 1930s. By 1941, the first fully electronic control system was tested on a Heinkel He 111. The Avro Canada CF-105 Arrow became the first non-experimental aircraft to fly with FBW in 1958.

Avro Arrow 04
Avro Arrow 04

Later that year, the North American A-5 Vigilante became the first to enter operational service with the technology. In 1968, the Apollo Lunar Landing Training Vehicle (LLTV) flew as a pure electronic system with no mechanical backup.

Fly by wire
Fly by wire

Safety and redundancy are critical in fly-by-wire design. If all flight control computers fail, an aircraft becomes uncontrollable. To prevent this, engineers use redundant computers, such as triplex or quadruplex systems. A quadruplex system uses four independent channels to ensure signals still arrive if one or two channels fail. Some aircraft, like the Panavia Tornado, keep a basic hydro-mechanical backup for limited control.

F-8C FBW
F-8C FBW

Before flight, pilots often use Built-in Test Equipment (BITE) to check the system. This allows the computer to perform automatic movement steps to ensure everything is working correctly.

Significant milestones in commercial aviation highlight the impact of FBW. The Airbus A320 was the first mass-produced airliner with digital fly-by-wire controls in 1988.

Airbus-319-cockpit
Airbus-319-cockpit

As of June 2024, over 11,000 A320 family aircraft are operational worldwide. Boeing adopted fly-by-wire for the 777 in 1994. The 777 uses Primary Flight Computers (PFCs) connected via ARINC 629 buses. These computers use the Ada programming language to manage flight. They also provide "envelope protection." This feature prevents the pilot from causing accidental stalls or excessive structural stress. This technology connects electronic control to the broader goal of flight safety and efficiency.

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🖼️ Images & Media (7)
File:Airbus-319-cockpit.jpg
Airbus-319-cockpit.jpg
File:Feedback loop with descriptions.svg
Feedback loop with descriptions.svg
File:Avro Arrow 04.jpg
Avro Arrow 04.jpg
File:F-8C FBW.jpg
F-8C FBW.jpg
File:Fly by wire.jpg
Fly by wire.jpg
File:F-BUAD A300B2-C1 Airbus Industry(3rd prototype) Farnborough SEP86 (12609347665).jpg
F-BUAD A300B2-C1 Airbus Industry(3rd...
File:'Sea Eagle 501' Atsugi route 4 departure. (8382546777).jpg
'Sea Eagle 501' Atsugi route 4 departure....
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