Fly By Wire Control Systems

Aircraft flight control systems – Wikipedia, the free encyclopedia

Fly By Wire

Mechanical and hydro-mechanical flight control systems are heavy and require careful routing of flight control cables through the aircraft using systems of pulleys, cranks, wires and, with hydraulically-assisted controls, hydraulic pipes. Both systems often require redundant backup to deal with failures, which again increases weight. Furthermore, both have limited ability to compensate for changing aerodynamic conditions. Dangerous characteristics such as stalling, spinning and Pilot-induced oscillation (PIO), which depend mainly on the stability and structure of the aircraft concerned rather than the control system itself, can still occur with these systems.

By using electrical control circuits combined with computers, designers can save weight, improve reliability, and use the computers to mitigate the undesirable characteristics mentioned above. Advanced modern fly-by-wire systems are also used to control otherwise unstable fighter aircraft.

The words “Fly-by-Wire” (FBW) imply an electrically-signaled only control system. However, the term is generally used in the sense of computer-configured controls, where a computer system is interposed between the operator and the final control actuators or surfaces. This modifies the manual inputs of the pilot in accordance with control parameters. These are carefully developed and validated in order to produce maximum operational effect without compromising safety.

Fly-by-optics

Fly-by-optics is sometimes used instead of fly-by-wire because it can transfer data at higher speeds, and it is immune to electromagnetic interference. In most cases, the cables are just changed from electrical to fiber optic cables. Sometimes it is referred to as “Fly-by-light” due to its use of Fiber Optics. The data generated by the software and interpreted by the controller remain the same.

Power-by-wire

Having eliminated the mechanical circuits in fly-by-wire flight control systems, the next step is to eliminate the bulky and heavy hydraulic circuits. The hydraulic circuit is replaced by an electrical power circuit. The power circuits power electrical or self-contained electrohydraulic actuators that are controlled by the digital flight control computers. All benefits of digital fly-by-wire are retained.

The biggest benefits are weight savings, the possibility of redundant power circuits and tighter integration between the aircraft flight control systems and its avionics systems. The absence of hydraulics greatly reduces maintenance costs. This system is used in the Lockheed Martin F-35 and in Airbus A380 backup flight controls. The Boeing 787 will also incorporate some electrically operated flight controls (spoilers and horizontal stabilizer), which will remain operational with either a total hydraulics failure and/or flight control computer failure.

Intelligent Flight Control System

A newer flight control system, called Intelligent Flight Control System (IFCS), is an extension of modern digital fly-by-wire flight control systems. The aim is to intelligently compensate for aircraft damage and failure during flight, such as automatically using engine thrust and other avionics to compensate for severe failures such as loss of hydraulics, loss of rudder, loss of ailerons, loss of an engine, etc. Several demonstrations were made on a flight simulator where a Cessna-trained small-aircraft pilot successfully landed a heavily-damaged full-size concept jet, without prior experience with large-body jet aircraft. This development is being spearheaded by NASA Dryden Flight Research Center.[9] It is reported that enhancements are mostly software upgrades to existing fully computerized digital fly-by-wire flight control systems.

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