Editing Stall (fluid dynamics) (section)

==Warning and safety devices==
Fixed-wing aircraft can be equipped with devices to prevent or postpone a stall or to make it less (or in some cases more) severe, or to make recovery easier.
* An '''aerodynamic twist''' can be introduced to the wing with the leading edge near the wing tip twisted downward. This is called '''washout''' and causes the [[wing root]] to stall before the wing tip. This makes the stall gentle and progressive. Since the stall is delayed at the wing tips, where the [[aileron]]s are, roll control is maintained when the stall begins.
* A '''[[stall strip]]''' is a small sharp-edged device that, when attached to the leading edge of a wing, encourages the stall to start there in preference to any other location on the wing. If attached close to the wing root, it makes the stall gentle and progressive; if attached near the wing tip, it encourages the aircraft to drop a wing when stalling.
* A '''[[Wing fence|stall fence]]''' is a flat plate in the direction of the [[Chord (aircraft)|chord]] to stop separated flow progressing out along the wing<ref>{{Cite web |url=http://www.centennialofflight.gov/essay/Theories_of_Flight/Transonic_Wings/TH20G6.htm |title=Stall fences and vortex generators |access-date=2009-04-25 |archive-url=https://web.archive.org/web/20090508032211/http://www.centennialofflight.gov/essay/Theories_of_Flight/Transonic_Wings/TH20G6.htm |archive-date=2009-05-08 |url-status=dead }}</ref>
* '''[[Vortex generator]]s''', tiny strips of metal or plastic placed on top of the wing near the leading edge that protrude past the [[boundary layer]] into the free stream. As the name implies, they energize the boundary layer by mixing free stream airflow with boundary layer flow, thereby creating vortices, this increases the [[momentum]] in the boundary layer. By increasing the momentum of the boundary layer, airflow separation and the resulting stall may be delayed.
* An '''anti-stall strake''' is a [[leading edge extension]] that generates a [[vortex]] on the wing upper surface to postpone the stall.
* A '''[[stick pusher]]''' is a mechanical device that prevents the pilot from stalling an aircraft. It pushes the elevator control forward as the stall is approached, causing a reduction in the angle of attack. In generic terms, a stick pusher is known as a ''stall identification device'' or ''stall identification system''.<ref>US [[Federal Aviation Administration]], Advisory Circular 25-7A ''Flight Test Guide for Certification of Transport Category Airplanes'', paragraph 228.</ref>
* A '''[[stick shaker]]''' is a mechanical device that shakes the pilot's controls to warn of the onset of stall.
* A '''stall warning''' is an electronic or mechanical device that sounds an [[buzzer|audible warning]] as the stall speed is approached. The majority of aircraft contain some form of this device that warns the pilot of an impending stall. The simplest such device is a ''stall warning horn'', which consists of either a [[pressure]] [[sensor]] or a movable metal tab that actuates a [[switch]] and produces an audible warning in response.
* An '''angle-of-attack indicator''' for light aircraft, the "AlphaSystemsAOA" and a nearly identical "'''lift reserve indicator'''", are both pressure-differential instruments that display margin above stall and/or angle of attack on an instantaneous, continuous readout. The General Technics CYA-100 displays true angle of attack via a magnetically coupled vane. An AOA indicator provides a visual display of the amount of available lift throughout its slow-speed envelope regardless of the many variables that act upon an aircraft. This indicator is immediately responsive to changes in speed, angle of attack, and wind conditions, and automatically compensates for aircraft weight, altitude, and temperature.
* An '''angle of attack limiter''' or an "alpha limiter" is a flight computer that automatically prevents pilot input from causing the plane to rise over the stall angle. Some alpha limiters can be disabled by the pilot.

Stall warning systems often involve inputs from a broad range of sensors and systems to include a dedicated angle of attack sensor.

Blockage, damage, or inoperation of stall and angle of attack (AOA) probes can lead to unreliability of the stall warning and cause the stick pusher, overspeed warning, autopilot, and yaw damper to malfunction.<ref>{{Cite web |url=http://www.ainonline.com/news/single-news-page/article/harco-probes-still-causing-eclipse-airspeed-problems/ |title=Harco Probes Still Causing Eclipse Airspeed Problems |access-date=2008-10-04 |archive-url=https://web.archive.org/web/20080926190738/http://www.ainonline.com/news/single-news-page/article/harco-probes-still-causing-eclipse-airspeed-problems/ |archive-date=2008-09-26 |url-status=dead }}</ref>

If a forward [[canard (aeronautics)|canard]] is used for pitch control, rather than an aft tail, the canard is designed to meet the airflow at a slightly greater angle of attack than the wing. Therefore, when the aircraft pitch increases abnormally, the canard will usually stall first, causing the nose to drop and so preventing the wing from reaching its critical AOA. Thus, the risk of main-wing stalling is greatly reduced. However, if the main wing stalls, recovery becomes difficult, as the canard is more deeply stalled, and angle of attack increases rapidly.<ref>"Airplane stability and control" by Malcolm J. Abzug, E. Eugene Larrabee. Chapter 17. {{ISBN|0-521-80992-4}}.</ref>

If an aft tail is used, the wing is designed to stall before the tail. In this case, the wing can be flown at higher lift coefficient (closer to stall) to produce more overall lift.

Most military combat aircraft have an angle of attack indicator among the pilot's instruments, which lets the pilot know precisely how close to the stall point the aircraft is. Modern airliner instrumentation may also measure angle of attack, although this information may not be directly displayed on the pilot's display, instead driving a stall warning indicator or giving performance information to the flight computer (for fly-by-wire systems).