Leading-edge slat: Difference between revisions

A '''Slatsslat''' areis an [[aerodynamic]] surfacessurface on the leading edge of the [[wing]]s of a [[fixed-wing aircraft]]. whichWhen retracted, whenthe slat lies flush with the rest of the wing. A slat is deployed by sliding forward, allowopening a slot between the wing toand operatethe slat. Air from below the slat flows through the slot and replaces the boundary layer that has travelled at high speed around the leading edge of the slat, losing a highersignificant [[angleamount of attack]]its kinetic energy due to skin friction drag. AWhen higherdeployed, coefficientslats ofallow liftthe iswings producedto asoperate at a result ofhigher [[angle of attack]] andbefore speed, so bystalling. deployingWith slats deployed an aircraft can fly at slower speeds, orallowing it to take off and land in shorter distances. They are usually used whileduring takeoff and landing orand while performing low-speed maneuvers which may take the aircraft close to a [[stall (flight)|stall]],. butSlats are usually retracted in normal flight to minimize [[drag (physics)|drag]]. They decrease [[stall speed]].

Slats are one of several [[high-lift device]]s typically used on [[airliner]]s,aircraft suchintended asto operate within a wide range of speeds. Trailing-edge [[flap (aeronautics)|flap]] systems running along the trailing edge of the wing are common on all aircraft.

The [[chord (aeronautics)|chord]] of the slat is typically only a few percent of the wing chord. The slats may extend over the outer third of the wing, or they may cover the entire [[leading edge]]. Many early aerodynamicists, including [[Ludwig Prandtl]], believed that slats work by inducing a high energy stream to the flow of the main [[airfoil]], thus re-energizing its [[boundary layer]] and delaying stall.<ref>Theory of wing sections, Abbott and Doenhoff, Dover Publications</ref> In reality, the slat does not give the air in the slot a high velocity (it actually reduces its velocity) and also it cannot be called high-energy air since all the air outside the actual boundary layers has the same [[Enthalpy|total heat]]. The actual effects of the slat are:<ref>High-Lift Aerodynamics, A.M.O. Smith, Journal of Aircraft, 1975</ref><ref name="Smith1975">[http://www.arvelgentry.com/amo/High-Lift_Aerodynamics.pdf High-Lift Aerodynamics, by A. M. O. Smith, McDonnell Douglas Corporation, Long Beach, June 1975] {{webarchive|url=https://web.archive.org/web/20110707172637/http://www.arvelgentry.com/amo/High-Lift_Aerodynamics.pdf |date=2011-07-07 }}</ref>

Slats were first developed by [[Gustav Lachmann]] in 1918. The stall-related crash in August 1917 of a [[Rumpler]] C aeroplane prompted Lachmann to develop the idea, and a small wooden model was built in 1917 in [[Cologne]]. In Germany in 1918 Lachmann presented a patent for leading-edge slats.<ref>{{cite web |url=http://naca.central.cranfield.ac.uk/reports/1921/naca-tn-71.pdf |title=Experiments with slotted wings |author = Gustav Lachmann - National Advisory Committee for Aeronautics |date = November 1921 |access-date=2018-10-14 |archive-date=2012-11-29 |archive-url=https://web.archive.org/web/20121129083659/http://naca.central.cranfield.ac.uk/reports/1921/naca-tn-71.pdf |url-status=dead }}</ref> However, the German patent office at first rejected it, as the office did not believe the possibility of postponing the stall by dividing the wing.

Independently of Lachmann, [[Handley Page]] Ltd in Great Britain also developed the slotted wing as a way to postpone the stall by delaying separation of the flow from the upper surface of the wing at high angles of attack, and applied for a patent in 1919; to avoid a patent challenge, they reached an ownership agreement with Lachmann. That year, an [[Airco DH.9]] was fitted with slats and test flown.<ref>{{citation |first=F.|last= Handley Page |url=https://www.flightglobal.com/pdfarchive/view/1921/1921%20-%200844.html |title= Developments In Aircraft Design By The Use Of Slotted Wings | archive-url=https://web.archive.org/web/20121103181345/http://www.flightglobal.com/pdfarchive/view/1921/1921%20-%200844.html |archive-date=2012-11-03 |work=Flight |date= December 22, 1921 | page= 844 |via=Flightglobal Archive |volume= XIII |number=678 |url-status=live }}</ref> Later, an [[Airco DH.9A]] was modified as a monoplane with a large wing fitted with full-span leading edge slats and trailing-edge ailerons (i.e. what would later be called trailing-edge flaps) that could be deployed in conjunction with the leading-edge slats to test improved low-speed performance. This was later known as the [[Handley Page H.P.20]]<ref>F. Handley Page [http://www.flightglobal.com/pdfarchive/view/1921/1921%20-%200845.html "Developments In Aircraft Design By The Use Of Slotted Wings"] {{webarchive|url=https://web.archive.org/web/20121103181419/http://www.flightglobal.com/pdfarchive/view/1921/1921%20-%200845.html |date=2012-11-03 }} ''Flight'', December 22nd 1921, photo page 845 of converted D.H.4 for testing of slotted wings</ref> Several years later, having subsequently taken employment at the Handley-Page aircraft company, Lachmann was responsible for a number of aircraft designs, including the [[Handley Page Hampden]].

During World War II, German aircraft commonly fitted a more advanced version of the slat that reduced [[Drag (physics)|drag]] by being pushed back flush against the leading edge of the wing by [[air pressure]], popping out when the angle of attack increased to a critical angle. Notable slats of that time belonged to the German [[Fieseler Fi 156]] ''Storch''. These were similar in design to retractable slats, but were fixed and non-retractable. This design feature allowed the aircraft to take-offtakeoff into a light wind in less than 45&nbsp;m (150&nbsp;ft), and land in 18&nbsp;m (60&nbsp;ft). Aircraft designed by the [[Messerschmitt]] company employed automatic, spring-loaded leading-edge slats as a general rule, except for the [[Alexander Lippisch]]-designed [[Messerschmitt Me 163B]] ''Komet'' rocket fighter, which instead used fixed slots built integrally with, and just behind, the wing panel's outer leading edges.