A flight control system consists of the flight control surfaces, the respective cockpit controls, connecting linkage, and necessary operating mechanisms to control aircraft in flight.

The fundamentals of aircraft controls have been explained in aeronautics. Discussion here centers on the underlying mechanisms of the flight controls. Generally the cockpit controls are arranged like this: To meet Wikipedias quality standards, this article or section may require cleanup. ...

• Control yoke for roll which moves the ailerons
• Control column for pitch which moves the elevators
• Rudder pedals for yaw which moves the rudder

Many aircraft use a control stick for both roll and pitch, and the rudder pedals for yaw. Aileron location on a Piper PA-28. ... For other meanings of elevator see Elevator (disambiguation). ... The worlds oldest depiction of a rudder. ...

Flight control systems

Mechanical

Mechanical flight control systems are the most basic designs. They were used in early aircraft and currently in small aeroplanes where the aerodynamic forces are not excessive. The flight control systems uses a collection of mechanical parts such as rods, cables, pulleys and sometimes chains to transmit the forces of the cockpit controls to the control surfaces. The Cessna Skyhawk is a typical example. 1971 Cessna 172 The Cessna 172 Skyhawk is a four-seat, single-engine, high-wing airplane that is probably the most popular flight training aircraft in the world. ...

Since an increase in control surface area in bigger and faster aircraft leads to a large increase in the forces needed to move them, complicated mechanical arrangements are used to extract maximum mechanical advantage in order to make the forces required bearable to the pilots. This arrangement is found on bigger or higher performance propeller aircraft such as the Fokker 50. In physics and engineering, mechanical advantage (MA) is the factor by which a mechanism multiplies the force put into it. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... Fokker F50 VLM Airlines Fokker F50 The Fokker F50 was a small turboprop-powered airliner designed as a refinement of and successor to the highly successful Fokker Friendship. ...

Some mechanical flight control systems use servo tabs that provide aerodynamic assistance to reduce complexity. Servo tabs are small surfaces hinged to the control surfaces. The mechanisms move these tabs, aerodynamic forces in turn move the control surfaces reducing the amount of mechanical forces needed. This arrangement was used in early piston-engined transport aircraft and in early jet transports such as the mostly mechanical Boeing 707. The Boeing 707 is a four engined commercial passenger jet aircraft developed by Boeing in the early 1950s. ...

Hydromechanical

The complexity and weight of a mechanical flight control systems increases considerably with size and performance of the airplane. Hydraulic power overcomes these limitations. With hydraulic flight control systems aircraft size and performance are limited by economics rather than a pilot's strength. ...

A hydraulic flight control systems has 2 parts:

• The mechanical circuit
• The hydraulic circuit

The mechanical circuit links the cockpit controls with the hydraulic circuits. Like the mechanical flight control systems, it is made of rods, cables, pulleys, and sometimes chains.

The hydraulic circuit has hydraulic pumps, pipes, valves and actuators. The actuators are powered by the hydraulic pressure generated by the pumps in the hydraulic circuit. The actuators convert hydraulic pressure into control surface movements. The servo valves control the movement of the actuators.

The pilot's movement of a control causes the mechanical circuit to open the matching servo valves in the hydraulic circuit. The hydraulic circuit powers the actuators which then move the control surfaces.

This arrangement is found in older jet transports and high performance aircraft. Examples include the Antonov An-225 and the Lockheed SR-71.-1... A trainer version of the USAF SR-71. ...

Artificial feel devices

In mechanical flight control systems, the aerodynamic forces on the control surfaces are transmitted through the mechanisms and can be felt by the pilot. This gives tactile feedback of airspeed and aids flight safety.

Hydromechanical flight control systems lack this "feel". The aerodynamic forces are only felt by the actuators. Artificial feel devices are fitted to the mechanical circuit of the hydromechanical flight control systems to simulate this "feel". They increase resistance with airspeed and vice-versa. The pilots feel as if they are flying an aircraft with a mechanical flight control systems.

Fly-by-wire

Mechanical and hydraulic flight control systems are heavy and require careful routing of flight control cables through the airplane using systems of pulley and cranks. Both systems often require redundant backup, which further increases weight. Furthermore, both have limited ability to compensate for changing aerodynamic conditions. Hydraulically powered cylinders are visible on this excavator. ... Aerodynamics (shaping of objects that affect the flow of air, liquid or gas) is a branch of fluid dynamics concerned with the study of forces and gas flows. ...

By using computers and electrical linkages, designers can save weight and improve reliability. Electronic fly-by-wire systems can respond more flexibly to changing aerodynamic conditions, by tailoring flight control surface movements so that airplane response to control inputs is consistent for all flight conditions. Electronic systems require less maintenance, whereas mechanical and hydraulic systems require lubrication, tension adjustments, leak checks, fluid changes, etc. Furthermore putting circuitry between pilot and aircraft can enhance safety; for example the control system can prevent a stall, or can stop the pilot from overstressing the airframe. The tower of a personal computer. ... Aircraft flight controls allow a pilot to adjust and control the aircrafts flight attitude. ... In aerodynamics, a stall is a condition in which an excessive angle of attack causes loss of lift due to disruption of airflow. ...

A fly-by-wire system literally replaces physical control of the aircraft with an electrical interface. The pilot's commands are converted to electronic signals, and flight control computers determine how best to move the actuators at each control surface to provide the desired response. Those actuators initially are usually hydraulic, but electric actuators have been investigated. An actuator is the mechanism by which an agent acts upon an environment. ... An actuator is the mechanism by which an agent acts upon an environment. ...

The main concern with fly-by-wire systems is reliability. While traditional mechanical or hydraulic control systems usually fail gradually, the loss of all flight control computers will immediately render the airplane uncontrollable. For this reason, most fly-by-wire systems incorporated redundant computers and some kind of mechanical or hydraulic backup. This may seem to negate some advantages of fly-by-wire, but the redundant systems can be simpler, lighter, and offer only limited capability since they are for emergency use only.

Analog

The fly-by-wire flight control systems eliminates the complexity, fragility and weight of the mechanical circuit of the hydromechanical flight control systems and replaces it with an electrical circuit. The cockpit controls now operate signal transducers which generate the appropriate commands. The commands are processed by an electronic controller. The autopilot is now part of the electronic controller. A simple detachable autopilot on a sailboat. ...

The hydraulic circuits are similar except that mechanical servo valves are replaced with electrically controlled servo valves. The valves are operated by the electronic controller. This is the simplest and earliest configuration, an analog fly-by-wire flight control systems, first fitted to the Avro Vulcan in the 1950s. The Avro Vulcan was a British delta-wing subsonic bomber, operated by the Royal Air Force from 1953 until 1984. ...

In this configuration, the flight control systems must simulate "feel". The electronic controller controls electrical feel devices that provide the appropriate "feel" forces on the manual controls. This is still used in the EMBRAER 170 and EMBRAER 190 and was used in Concorde, the first fly-by-wire airliner. The EMBRAER 190 initial flight The EMBRAER E-Jets are a series of twin-engine jet airliners, produced in Brazil. ... The EMBRAER 190 initial flight The EMBRAER E-Jets are a series of twin-engine jet airliners, produced in Brazil. ... The Aérospatiale-BAC Concorde supersonic transport (SST), along with the Tupolev Tu-144, was one of only two models of supersonic passenger airliners to have seen commercial service. ...

On more sophisticated versions, analog computers replaced the electronic controller. The cancelled supersonic Canadian fighter, the Avro CF-105 Arrow, was built this way in the 1950s. Analog computers also allowed some customization of flight control characteristics, including relaxed stability. This was exploited by the early versions of F-16, giving it impressive maneuverability. The Avro CF-105 Arrow was a delta-wing interceptor aircraft, designed and built in Ontario, Canada by Avro Canada during a short period of time in the 1950s. ... In aeronautical engineering, relaxed stability refers to airplanes with no inherent natural stability, at least at low speeds. ... The F-16 Fighting Falcon is a modern multi-role jet fighter aircraft built in the United States and used by dozens of countries all over the world. ...

Digital

A digital fly-by-wire flight control system is similar to its analog counterpart. However, the signal processing is done by digital computers. The pilot literally can "fly-via-computer". This increases flexibility as the digital computers can receive input from any aircraft sensor. It also increases stability, because the system is less dependent on the values of critical electrical components in an analog controller.

F-8C Crusader digital fly-by-wire testbed.

The Federal Aviation Administration (FAA) of the United States adopted the RTCA/DO-178B, titled "Software Considerations in Airborne Systems and Equipment Certification", as the certification standard for aviation software. Any safety-critical component in a digital fly-by-wire system including control laws and the operation system will have to be certified to DO-178B Level A, which is applicable for potentially catastrophic failures. Text and image from nasa. ... Text and image from nasa. ... F-8C digital fly-by-wire testbed (NASA) The F-8 Crusader (originally F8U) was an aircraft carrier-based fighter aircraft built by Chance-Vought of Dallas, Texas. ... FAA redirects here. ... Radio Technical Commission for Aeronautics, Inc. ... Avionics software is embedded software with legally-mandated safety and reliability concerns, that is used in avionics. ... A life-critical system or safety-critical system is a system whose failure or malfunction may result in a) death or serious injury to people, or b) loss or severe damage to equipment or c) environmental harm. ... In computing, an operating system (OS) is the system software responsible for the direct control and management of hardware and basic system operations. ...

Nonetheless the top concern for computerized, digital fly-by-wire systems is reliability, even more than analog systems. This is because a computer running software is the only control path between pilot and control surfaces. If the computer software crashes, the pilot cannot control the aircraft. Therefore virtually all fly-by-wire systems are triply or quadruply redundant: they have three or four computers in parallel, and three or four separate wires to each control surface. If one or two computers crash, the others continue working. In addition most early digital fly-by-wire aircraft also had an analog electric, mechanical or hydraulic backup control system. Aircraft flight controls allow a pilot to adjust and control the aircrafts flight attitude. ... In engineering, the duplication of critical components of a system with the intention of increasing reliability of the system, usually in the case of a backup or fail-safe, is called redundancy. ...

The computers read positions and forces from the pilot's controls and aircraft sensors. They calculate differential equations that move the flight controls to carry out the intentions of the pilot. Graph of a differential equation In mathematics, a differential equation is an equation in which the derivatives of a function appear as variables. ...

The program in the digital computers let aircraft designers tailor an aircraft's handling characteristics precisely. For example the software can prevent the aircraft from being handled dangerously by preventing pilots from exceeding preset limits (the aircraft's envelope). Software can also be used to filter control inputs to avoid pilot-induced oscillation. Pilot-induced oscillations (PIO) occur when the pilot of an aircraft inadvertently commands an often increasing series of corrections in opposite directions, each an attempt to correct for the previous overcorrection with an overcorrection in the opposite direction. ...

Sidesticks or conventional control yokes can be used to fly such an aircraft. While the side stick offers the advantages of being lighter, mechanically simpler, and unobtrusive, Boeing considered the lack of visual feedback from the side stick a problem, and so uses conventional yokes in the 777 and the upcoming 787. In aviation, a yoke is a control used in most transport airplanes, that is also called a joystick or steering wheel. ... The Boeing Company (NYSE: BA, TYO: 7661 ) is an aerospace and defense corporation headquartered in Chicago, Illinois. ... The Boeing 777 is a family of long-range wide-body twin-engine airliners built by Boeings Commercial Airplanes division. ... The Boeing 787 Dreamliner is a mid-sized wide body, twin engined passenger airliner currently under development by Boeing and scheduled to enter service in 2008. ...

As the computers continuously fly the aircraft, pilot workload is reduced. It is now possible to fly aircraft with relaxed stability. The primary benefit for military aircraft is more responsive flight performance. Digital flight control systems enabled inherently unstable aircraft such as Lockheed Martin F-117 Nighthawk to fly. A modified NASA F-8C Crusader was the first digital fly-by-wire aircraft, in 1972. The US Space Shuttle (first flown in 1982) has digital fly-by-wire controls. In 1984, the Airbus A320 was the first airliner with digital fly-by-wire controls. In 2005, the Dassault Falcon 7X was the first business jet with fly-by-wire controls. In aeronautical engineering, relaxed stability refers to airplanes with no inherent natural stability, at least at low speeds. ... The Lockheed F-117A Nighthawk, nicknamed “The Black Jet”[2], is the worlds first operational aircraft completely designed around stealth technology. ... NASA Logo Listen to this article · (info) This audio file was created from the revision dated 2005-09-01, and does not reflect subsequent edits to the article. ... F-8C digital fly-by-wire testbed (NASA) The F-8 Crusader (originally F8U) was an aircraft carrier-based fighter aircraft built by Chance-Vought of Dallas, Texas. ... This article is about the NASA Space Shuttle vehicle. ... The Airbus A320 is a short-to-medium range commercial passenger aircraft manufactured by Airbus. ... The Falcon 7X is a business jet manufactured by Dassault Aviation. ... Business jet (slang, Bizjet) is a term for a jet aircraft, usually of modest size, designed for transporting small groups of business people for commercial reasons at a time convenient to their business needs. ...

On military aircraft, fly-by-wire improves combat survivability because it avoids hydraulic failure. A common reason behind the loss of military aircraft in combat is damage causing hydraulic leaks leading to loss of control. Most military aircraft have several completely redundant hydraulic systems, but hydraulic lines are often routed together, and can be damaged together. With a fly-by-wire system, wires can be more flexibly routed, are easier to protect and less susceptible to damage than hydraulic lines.

For airliners, redundancy improves safety, but fly-by-wire also improves economy because the elimination of heavy mechanical items reduces weight.

Boeing and Airbus differ in their FBW philosophies. In Airbus aircraft, the computer always retains ultimate control and will not permit the pilot to fly outside the normal flight envelope. In a Boeing 777, the pilot can override the system, allowing the plane to be flown outside this envelope in emergencies. The pattern started by Airbus A320 has been continued with the Airbus family and the Boeing 777. The Airbus A320 is a short-to-medium range commercial passenger aircraft manufactured by Airbus. ... The Boeing 777 is a family of long-range wide-body twin-engine airliners built by Boeings Commercial Airplanes division. ...

Aircraft-engine integration

The advent of FADEC (full authority digital engine control) engines permits operation of the flight control systems and autothrottles for the engines to be fully integrated. On modern military aircraft other systems such as autostabilization, navigation, radar and weapons system are all integrated with the flight control systems. FADEC is the acronym for Full Authority Digital Engine Control. ... An autothrottle (automatic throttle) allows the pilot to control the power setting of an of an aircrafts engines automatically. ...

FADEC allows maximum performance to be extracted from the aircraft without fear of engine misoperation, airplane damage or high pilot workloads.

In the civil field, the integration increases flight safety and economy. The Airbus A320 and its fly-by-wire brethren are protected from low-speed stall. In such conditions, the flight control systems commands the engines to increase thrust without pilot intervention. In economy cruise modes, the flight control systems adjusts the throttles and fuel tank selections more precisely than all but the most skillful pilots. FADEC reduces rudder drag needed to compensate for sideways flight from unbalanced engine thrust. The fuel management controls keep the aircraft's attitude accurately trimmed with fuel weight, rather than draggy aerodynamic trims in the elevators. The Airbus A320 is a short-to-medium range commercial passenger aircraft manufactured by Airbus. ...

Cars

Fly by wire has now become mainstream enough to be used in mass production motor cars. The Toyota Prius Hybrid takes account of pedal action and gear changes to work out how much petrol is required, what CVT gearing to use, and how to apply the electric motor/generator. Mainstream is, generally, the common current of thought of the majority. ... This article or section does not cite its references or sources. ... Prius may refer to: Hitachi Flora Prius, a personal computer. ... // A hybrid vehicle (HV) is a vehicle using an on-board rechargeable energy storage system (RESS) and a fuelled power source for vehicle propulsion. ... Spur gears found on a piece of farm equipment. ... Gasoline, as it is known in North America, or petrol, in many Commonwealth countries (sometimes also called motor spirit) is a petroleum-derived liquid mixture consisting primarily of hydrocarbons, used as fuel in internal combustion engines. ... A continuously variable transmission (CVT) is a type of automatic transmission that can change the gear ratio (gears are not generally involved) to any arbitrary setting within the limits. ... Rotating magnetic field as a sum of magnetic vectors from 3 phase coils. ... Electrical generator Generator (Mathematics) ...

See also electronic throttle control. Electronic throttle control (ETC) is an automobile technology which severs the direct link between the accelerator pedal and the throttle. ...

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. The data generated by the software and interpreted by the controller remain the same. A bundle of optical fibers. ...

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 F-35 Joint Strike Fighter The F-35 Joint Strike Fighter (JSF) is a fighter plane currently in early development by Lockheed Martin (with partners Northrop Grumman and BAE SYSTEMS.) The primary customers are the United States armed forces and the United Kingdom (RN and RAF), but the Netherlands... The Airbus A380 is a double-deck, four-engined airliner manufactured by Airbus S.A.S. It first flew on April 27, 2005 from Toulouse in France. ...

Intelligent

A newer flight control system, called Intelligent Flight Control System, 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[1]. It is reported that enhancement is mostly a software upgrade to an existing fully computerized digital fly-by-wire flight control systems. Cessna Aircraft Company, located in Wichita, Kansas, is a manufacturer of general aviation aircraft, from small two-seat, single-engine airplanes to business jets. ... NASA logo Listen to this article · (info) This audio file was created from an article revision dated 2005-09-01, and does not reflect subsequent edits to the article. ...

External links

• Airbus A380 cockpit.

See also

• MIL-STD-1553 A standard data bus for fly-by-wire.

MIL-STD-1553 is a DoD Military Standard which defines the Mechanical, Electrical and Functional Characteristics of a serial data bus originally designed for use with military avionics. ...

Bibliography

• Cary R. Spitzer, Ed., The Avionics Handbook, CRC Press, ISBN 0-8493-8348-X

• R. F. Stengel, "Toward Intelligent Flight Control," IEEE Trans. Systems, Man, and Cybernetics,

Vol. 23, No. 6, Nov-Dec 1993, pp. 1699-1717. The CRC Press, LLC is a publishing group which specializes in producing technical books in a wide range of subjects. ...