Editing Aircraft flight control system

{{Short description|How aircraft are controlled}}
{{Redirect-distinguish|Flight Control|Flight Control (video game)}}
{{about-distinguish|the fixed-wing concept|Helicopter flight controls|Orbital spaceflight control}}
{{more citations needed|date=October 2009}} 
[[File:ControlSurfaces.gif|thumb|upright=1.14|A typical aircraft's primary flight controls in motion]]

A conventional [[Fixed-wing aircraft|fixed-wing]] '''aircraft flight control system''' ('''AFCS''') consists of [[flight control surfaces]], the respective cockpit controls, connecting linkages, and the necessary operating mechanisms to control an aircraft's direction in flight. [[Aircraft engine controls]] are also considered flight controls as they change speed.

The fundamentals of aircraft controls are explained in [[flight dynamics (fixed-wing aircraft)|flight dynamics]]. This article centers on the operating mechanisms of the flight controls. The basic system in use on aircraft first appeared in a readily recognizable form as early as April 1908, on [[Louis Blériot]]'s [[Blériot VIII]] pioneer-era monoplane design.<ref>{{cite book |title=Blériot XI, The Story of a Classic Aircraft |last=Crouch |first=Tom |year=1982 |publisher=Smithsonian Institution Press |isbn=978-0-87474-345-6 |pages=21 & 22 }}</ref>

==Cockpit controls==

=== Primary controls ===
[[File:Cessna 182D Skylane Cockpit.jpg|thumb|Cockpit controls and [[Flight instruments|instrument panel]] of a [[Cessna 182]]D Skylane]]
Generally, the primary cockpit flight controls are arranged as follows:<ref name="SaR">Langewiesche, Wolfgang. [https://books.google.com/books?id=CPdDju21zt0C Stick and Rudder: An Explanation of the Art of Flying], McGraw-Hill Professional, 1990, {{ISBN|0-07-036240-8}}, {{ISBN|978-0-07-036240-6}}.</ref>
* A [[Yoke (aircraft)|control yoke]] (also known as a control column), [[centre stick]] or [[side-stick]] (the latter two also colloquially known as a control or [[joystick]]), governs the aircraft's [[Flight dynamics (aircraft)|roll]] and [[Flight dynamics (aircraft)|pitch]] by moving the [[ailerons]] (or activating [[wing warping]] on some very early aircraft designs) when turned or deflected left and right, and moves the [[elevator (aircraft)|elevators]] when moved backwards or forwards.
* [[Rudder pedals]], or the earlier, pre-1919 "rudder bar", control [[Flight dynamics (aircraft)|yaw]] by moving the [[rudder]]; the left foot forward will move the rudder left for instance.
* [[Thrust lever]] or [[throttle]], which controls engine speed or [[thrust]] for powered aircraft.

The control [[Yoke (aeronautics)|yokes]] also vary greatly among aircraft. There are yokes where roll is controlled by rotating the yoke clockwise/counterclockwise (like steering a car) and pitch is controlled by moving the control column towards or away from the pilot, but in others the pitch is controlled by sliding the yoke into and out of the instrument panel (like most Cessnas, such as the 152 and 172), and in some the roll is controlled by sliding the whole yoke to the left and right (like the Cessna 162). Centre sticks also vary between aircraft. Some are directly connected to the control surfaces using cables,<ref>{{Cite web |url=http://www.centennialofflight.net/essay/Theories_of_Flight/control/TH28.htm |title=Control surfaces directly controlled using cables |access-date=2017-01-25 |archive-url=https://web.archive.org/web/20170202024101/http://www.centennialofflight.net/essay/Theories_of_Flight/control/TH28.htm |archive-date=2017-02-02 |url-status=live }}</ref> others (fly-by-wire airplanes) have a computer in between which then controls the electrical actuators.

[[File:Sports Aviation - Issy-les-Moulineaux (10 septembre) - Le Blériot VIII … (7843390842).jpg|thumb|right|Blériot VIII at [[Issy-les-Moulineaux]], the first flightworthy aircraft design to have the initial form of modern flight controls for the pilot]]
Even when an aircraft uses variant flight control surfaces such as a [[V-tail|V-tail ruddervator]], [[flaperon]]s, or [[elevon]]s, because these various combined-purpose control surfaces control rotation about the same three axes in space, the aircraft's flight control system will still be designed so that the stick or yoke controls pitch and roll conventionally, as will the rudder pedals for yaw.<ref name="SaR" />  The basic pattern for modern flight controls was pioneered by French aviation figure [[Robert Esnault-Pelterie]], with fellow French aviator [[Louis Blériot]] popularizing Esnault-Pelterie's control format initially on Louis' [[Blériot VIII]] monoplane in April 1908, and standardizing the format on the July 1909 Channel-crossing [[Blériot XI]]. Flight control has long been taught in such fashion for many decades, as popularized in [[ab initio]] instructional books such as the 1944 work [[Stick and Rudder]].

In some aircraft, the control surfaces are not manipulated with a linkage. In ultralight aircraft and motorized hang gliders, for example, there is no mechanism at all. Instead, the pilot just grabs the lifting surface by hand (using a rigid frame that hangs from its underside) and moves it.{{Citation needed|date=March 2012}}

===Secondary controls===
{{Main|Trim tab|Flap (aircraft)|Air brake (aircraft)|Spoiler (aeronautics)|Leading edge slats|Variable-sweep wing}}
In addition to the primary flight controls for roll, pitch, and yaw, there are often secondary controls available to give the pilot finer control over flight or to ease the workload.  The most commonly available control is a wheel or other device to control [[Flight control surfaces#Elevator trim|elevator trim]], so that the pilot does not have to maintain constant backward or forward pressure to hold a specific pitch [[Aircraft attitude|attitude]]<ref>Thom,1988. p. 87.</ref> (other types of trim, for [[rudder]] and [[ailerons]], are common on larger aircraft but may also appear on smaller ones).  Many aircraft have [[flap (aircraft)|wing flaps]], controlled by a switch or a mechanical lever or in some cases are fully automatic by computer control, which alter the shape of the wing for improved control at the slower speeds used for take-off and landing.   Other secondary flight control systems may include [[Leading edge slats|slats]], [[Spoiler (aeronautics)|spoilers]], [[Air brake (aircraft)|air brakes]] and [[variable-sweep wing]]s.

==Flight control systems==

===Mechanical===
[[File:Tiger cables.JPG|thumb|right|[[de Havilland Tiger Moth]] elevator and rudder cables]] 
Mechanical or manually operated flight control systems are the most basic method of controlling an aircraft. They were used in early aircraft and are currently used in small aircraft where the aerodynamic forces are not excessive. Very early aircraft, such as the [[Wright Flyer|Wright Flyer I]], [[Blériot XI]] and [[Fokker Eindecker]] used a system of [[wing warping]] where no conventionally hinged control surfaces were used on the wing, and sometimes not even for pitch control as on the Wright Flyer I and original versions of the 1909 [[Etrich Taube]], which only had a hinged/pivoting rudder in addition to the warping-operated pitch and roll controls.<ref>Taylor, 1990. p. 116.</ref> A manual flight control system uses a collection of mechanical parts such as pushrods, tension cables, pulleys, counterweights, and sometimes chains to transmit the forces applied to the cockpit controls directly to the control surfaces. [[Turnbuckle]]s are often used to adjust control cable tension. The [[Cessna Skyhawk]] is a typical example of an aircraft that uses this type of system. [[Gust lock]]s are often used on parked aircraft with mechanical systems to protect the control surfaces and linkages from damage from wind. Some aircraft have gust locks fitted as part of the control system.<ref>Thom,1988. p. 153.</ref>
 
Increases in the control surface area, and the higher airspeeds required by faster aircraft resulted in higher aerodynamic loads on the flight control systems. As a result, the forces required to move them also become significantly larger. Consequently, complicated mechanical [[gear]]ing arrangements were developed to extract maximum [[mechanical advantage]] in order to reduce the forces required from the pilots.<ref name="Taylor118">Taylor, 1990. p. 118.</ref> This arrangement can be found on bigger or higher performance [[Propeller (aircraft)|propeller]] aircraft such as the [[Fokker 50]].

Some  mechanical flight control systems use [[servo tab]]s that provide aerodynamic assistance. Servo tabs are small surfaces hinged to the control surfaces. The flight control mechanisms move these tabs, aerodynamic forces in turn move, or assist the movement of 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.<ref>Thom,1988. p. 86.</ref> The Boeing 737 incorporates a system, whereby in the unlikely event of total hydraulic system failure, it automatically and seamlessly reverts to being controlled via servo-tab.

===Hydro-mechanical===
[[File:Hydromechanical flight control system.png|thumb|right|Hydromechanical designs, consisting of a mechanical circuit and a hydraulic circuit, were used to reduce the complexity, weight, and limitations of mechanical flight controls systems.<ref>{{cite book |title=Pilot's Handbook of Aeronautical Knowledge |date=2016-08-24 |publisher=[[Federal Aviation Administration]] |page=6-2}}</ref>]]
The complexity and weight of mechanical flight control systems increase considerably with the size and performance of the aircraft. [[hydraulic machinery|Hydraulically powered control surface]]s help to overcome these limitations. With hydraulic flight control systems, the aircraft's size and performance are limited by economics rather than a pilot's muscular strength. At first, only-partially boosted systems were used in which the pilot could still feel some of the aerodynamic loads on the control surfaces (feedback).<ref name="Taylor118" />

A hydro-mechanical flight control system has two parts:
*The ''mechanical circuit'', which links the cockpit controls with the hydraulic circuits. Like the mechanical flight control system, it consists of rods, cables, pulleys, and sometimes chains.
*The ''hydraulic circuit'', which has hydraulic pumps, reservoirs, filters, 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 [[electro-hydraulic servo valve]]s control the movement of the actuators.

The pilot's movement of a control causes the mechanical circuit to open the matching servo valve in the hydraulic circuit. The hydraulic circuit powers the actuators which then move the control surfaces. As the actuator moves, the [[electro-hydraulic servo valve|servo valve]] is closed by a mechanical [[feedback]] linkage - one that stops movement of the control surface at the desired position.

This arrangement was found in the older-designed jet transports and in some high-performance aircraft. Examples include the [[Antonov An-225]] and the [[Lockheed SR-71]].

====Artificial feel devices====
With purely mechanical flight control systems, the aerodynamic forces on the control surfaces are transmitted through the mechanisms and are felt directly by the pilot, allowing tactile feedback of airspeed. With hydromechanical flight control systems, the load on the surfaces cannot be felt and there is a risk of overstressing the aircraft through excessive control surface movement. To overcome this problem, artificial feel systems can be used. For example, for the controls of the [[RAF]]'s [[Avro Vulcan]] jet [[bomber]] and the [[RCAF]]'s [[Avro Canada CF-105 Arrow]] supersonic interceptor (both 1950s-era designs), the required force feedback was achieved by a spring device.<ref>The Arrowheads, pages 57-58, 83-85 (for CF-105 Arrow only).</ref>  The [[Fulcrum (mechanics)|fulcrum]] of this device was moved in proportion to the square of the air speed (for the elevators) to give increased resistance at higher speeds. For the controls of the American [[Vought]] [[F-8 Crusader]] and the LTV [[A-7 Corsair II]] warplanes, a 'bob-weight' was used in the pitch axis of the control stick, giving force feedback that was proportional to the airplane's normal acceleration.{{Citation needed|date=July 2010}}

====Stick shaker====
{{Main|Stick shaker}}
A [[stick shaker]] is a device that is attached to the control column in some hydraulic aircraft. It shakes the control column when the aircraft is approaching [[Stall (fluid dynamics)|stall]] conditions. Some aircraft such as the [[McDonnell Douglas DC-10]] are equipped with a back-up electrical power supply that can be activated to enable the stick shaker in case of hydraulic failure.<ref>{{Cite journal|last=Daniels|first=Taumi|title=Regarding Pilot Usage of Display Technologies for Improving Awareness of Aircraft System States|url=https://ntrs.nasa.gov/api/citations/20200002619/downloads/20200002619.pdf|journal=NASA Langley Research Center}}</ref>

====Power-by-wire====
In most current systems the power is provided to the control actuators by high-pressure hydraulic systems. In fly-by-wire systems the valves, which control these systems, are activated by electrical signals. In power-by-wire systems, electrical actuators are used in favour of hydraulic pistons. The power is carried to the actuators by electrical cables. These are lighter than hydraulic pipes, easier to install and maintain, and more reliable. Elements of the [[F-35]] flight control system are power-by-wire.<ref>{{Cite web |url=https://www.aviationtoday.com/2001/05/01/power-by-wire/ |title=Power-By-Wire - Avionics<!-- Bot generated title --> |access-date=2018-08-09 |archive-url=https://web.archive.org/web/20170627215836/http://www.aviationtoday.com/2001/05/01/power-by-wire/ |archive-date=2017-06-27 |url-status=live |date=May 2001 }}</ref><ref>{{cite journal|title=Review on signal-by-wire and power-by-wire actuation for more electric aircraft|journal=Chinese Journal of Aeronautics|volume=30|issue=3|pages=857–870|doi=10.1016/j.cja.2017.03.013|year=2017|last1=Maré|first1=Jean-Charles|last2=Fu|first2=Jian|doi-access=free|bibcode=2017ChJAn..30..857M }}</ref><ref>{{Cite journal |title=C-141 and C-130 power-by-wire flight control systems - IEEE Conference Publication<!-- Bot generated title --> |pages=535–539 vol.2 |doi=10.1109/NAECON.1991.165802 |date=May 1991 |s2cid=109026952 }}</ref> The actuators in such an electro-hydrostatic actuation (EHA) system are self-contained hydraulic devices, small closed-circuit hydraulic systems. The overall aim is towards more- or all-electric aircraft and an early example of the approach was the [[Avro Vulcan]]. Serious consideration was given to using the approach on the Airbus A380.<ref>{{Cite web |url=https://www.aviationtoday.com/2001/10/01/a380-more-electric-aircraft/ |title=A380: 'More Electric' Aircraft - Avionics<!-- Bot generated title --> |access-date=2018-08-12 |archive-url=https://web.archive.org/web/20180812212940/https://www.aviationtoday.com/2001/10/01/a380-more-electric-aircraft/ |archive-date=2018-08-12 |url-status=live |date=October 2001 }}</ref>

===Fly-by-wire control systems===
{{Main|Fly-by-wire}}
A fly-by-wire (FBW) system replaces manual flight control of an aircraft with an electronic interface. The movements of flight controls are converted to electronic signals transmitted by wires (hence the term ''fly-by-wire''), and flight control computers determine how to move the [[actuators]] at each control surface to provide the expected response. Commands from the computers are also input without the pilot's knowledge to stabilize the aircraft and perform other tasks. Electronics for aircraft flight control systems are part of the field known as [[avionics]].

Fly-by-optics, also known as ''fly-by-light'', is a further development using [[fiber-optic cable]]s.

==Research==
Several technology research and development efforts exist to integrate the functions of flight control systems such as [[aileron]]s, [[elevator (aircraft)|elevators]], [[elevon]]s, [[flap (aircraft)|flap]]s, and [[flaperon]]s into wings to perform the aerodynamic purpose with the advantages of less: mass, cost, drag, [[inertia]] (for faster, stronger control response), complexity (mechanically simpler, fewer moving parts or surfaces, less maintenance), and [[radar cross section]] for [[stealth technology|stealth]]. These may be used in many [[unmanned aerial vehicle]]s (UAVs) and 6th generation [[fighter aircraft]]. Two promising approaches are flexible wings, and fluidics.

===Flexible wings===
{{Main article|Flexible wing}}

In flexible wings, also known as "morphing aerofoils", much or all of a wing surface can change shape in flight to deflect air flow much like an [[ornithopter]]. [[Adaptive compliant wing]]s are a military and commercial effort.<ref>{{citation |last=Scott |first=William B. |title=Morphing Wings |newspaper=Aviation Week & Space Technology |date=27 November 2006 |url=http://www.aviationweek.com/aw/ |access-date=2011-04-26 |archive-url=https://web.archive.org/web/20110426122028/http://www.aviationweek.com/aw/ |archive-date=2011-04-26 |url-status=live }}</ref><ref>{{cite web|url=http://www.flxsys.com/aerospace.shtml |title=FlexSys Inc.: Aerospace |access-date=26 April 2011 |url-status=dead |archive-url=https://web.archive.org/web/20110616074103/http://www.flxsys.com/aerospace.shtml |archive-date=16 June 2011 }}</ref><ref>{{cite web|url=http://www.flxsys.com/pdf/NATO_Conf_Paper-KOTA.pdf |title=Mission Adaptive Compliant Wing – Design, Fabrication and Flight Test |first1=Sridhar |last1=Kota |first2=Russell |last2=Osborn |first3=Gregory |last3=Ervin |first4=Dragan |last4=Maric |first5=Peter |last5=Flick |first6=Donald |last6=Paul |publisher=FlexSys Inc., Air Force Research Laboratory |location=Ann Arbor, MI; Dayton, OH, U.S.A. |access-date=26 April 2011 |url-status=dead |archive-url=https://web.archive.org/web/20120322211547/http://www.flxsys.com/pdf/NATO_Conf_Paper-KOTA.pdf |archive-date=22 March 2012 }}</ref> The [[X-53 Active Aeroelastic Wing]] was a US Air Force, [[NASA]], and [[Boeing]] effort. Notable efforts have also been made by FlexSys, who have conducted flight tests using flexible aerofoils retrofitted to a Gulf stream III aircraft.<ref>{{Cite web|title=FlexFoil|url=https://www.flxsys.com/flexfoil|access-date=2022-01-22|website=FlexSys|language=en-US}}</ref>

===Active Flow Control===
In [[active flow control]] systems, forces in vehicles occur via circulation control, in which larger and more complex mechanical parts are replaced by smaller, simpler fluidic systems (slots which emit air flows) where larger forces in fluids are diverted by smaller jets or flows of fluid intermittently, to change the direction of vehicles.<ref>{{cite journal
 |author=P John 
 |title=The flapless air vehicle integrated industrial research (FLAVIIR) programme in aeronautical engineering 
 |journal=Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 
 |volume=224 
 |issue=4 
 |pages=355–363 
 |publisher=London: Mechanical Engineering Publications 
 |year=2010 
 |url=http://journals.pepublishing.com/content/m9r3684g2874w026/
 |archive-url=https://web.archive.org/web/20180517223645/http://journals.pepublishing.com/content/m9r3684g2874w026
 |url-status=dead
 |archive-date=2018-05-17
 |issn=0954-4100 
 |doi=10.1243/09544100JAERO580 
|hdl=1826/5579 
 |s2cid=56205932 
 |hdl-access=free 
 }}</ref><ref>{{Cite web
 |title        = Showcase UAV Demonstrates Flapless Flight
 |publisher    = BAE Systems
 |year         = 2010
 |url          = http://www.baesystems.com/AboutUs/ShowcaseUAVDemonstratesFlaplessFlight/
 |access-date   = 2010-12-22
 |archive-url  = https://web.archive.org/web/20110707205548/http://www.baesystems.com/AboutUs/ShowcaseUAVDemonstratesFlaplessFlight/
 |archive-date = 2011-07-07
 |url-status     = dead
}}</ref> In this use, active flow control promises simplicity and lower mass, costs (up to half less), and [[inertia]] and response times. This was demonstrated in the [[BAE Systems Demon|Demon UAV]], which flew for the first time in the UK in September 2010.<ref>{{cite news |title=Demon UAV jets into history by flying without flaps |newspaper=Metro.co.uk |publisher=Associated Newspapers Limited |location=London |date=28 September 2010 |url=http://www.metro.co.uk/news/842292-plane-jets-into-history-by-flying-without-flaps |access-date=29 September 2010 |archive-url=https://web.archive.org/web/20110823110258/http://www.metro.co.uk/news/842292-plane-jets-into-history-by-flying-without-flaps |archive-date=2011-08-23 |url-status=live }}</ref>

== See also ==
<!--- alphabetical order -->
* [[Dual control (aviation)]]
* [[Flight envelope protection]]
* [[Flight with disabled controls]]
* [[Helicopter flight controls]]
* [[HOTAS]]
* [[Kite control systems]]
* [[List of airliner crashes involving loss of control]]
* [[Matthew Piers Watt Boulton]], inventor of the [[aileron]] (1868)
* [[Thrust vectoring]]
* [[Weight-shift control]]
* [[Wing warping]], an early method for controlling roll

== References ==

=== Notes ===
{{Reflist}}

===Bibliography===
{{Refbegin}}
* Spitzer, Cary R. ''The Avionics Handbook'', [[CRC Press]], {{ISBN|0-8493-8348-X}}
* Taylor, John W.R. ''The Lore of Flight'', London: Universal Books Ltd., 1990. {{ISBN|0-9509620-1-5}}.
* The Arrowheads (Richard Organ, Ron Page, Don Watson, Les Wilkinson).  ''Avro Arrow: the story of the Avro Arrow from its evolution to its extinction'',  Erin, Ontario, Canada:  Boston Mills Press 1980 (revised edition 2004).  {{ISBN|1-55046-047-1}}.
* Thom, Trevor. ''The Air Pilot's Manual 4-The Aeroplane-Technical''. 1988. Shrewsbury, Shropshire, England. Airlife Publishing Ltd. {{ISBN|1-85310-017-X}}
{{Refend}}
* USAF & NATO Report RTO-TR-015 AC/323/(HFM-015)/TP-1 (2001).

== External links ==
{{Commons category|Aircraft flight control systems}}
* [http://www.airliners.net/open.file?id=0957790&size=L&width=1000&height=679&sok=&photo_nr=Fly-by-wire: Airbus A380 cockpit].
* [https://web.archive.org/web/20081022071453/http://www.cheap-parking.net/airbus/ Airbus A380 cockpit - a 360-degree Panorama]
* [http://www.nasa.gov/centers/dryden/pdf/88794main_PCA.pdf ''Touchdown: the Development of Propulsion Controlled Aircraft at NASA-Dryden'' by Tom Tucker]

{{Aircraft components}}
{{Authority control}}

[[Category:Flight control systems]]

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