Editing Stabilator

{{Short description|Fully movable aircraft stabilizer}}
[[File:US Navy 051202-N-5832A-002 Air Department personnel run across the flight deck after the launch of an F-14D Tomcat.jpg|thumb|right|[[Grumman F-14 Tomcat]] jet fighter during a takeoff, with stabilators deflected upwards]]

A '''stabilator''' is a fully movable aircraft horizontal [[stabilizer (aircraft)|stabilizer]]. It serves the usual functions of longitudinal stability, control and stick force requirements<ref>Roskam, ''Airplane Design'', part III, Empennage layout, Longitudinal considerations</ref>  otherwise performed by the separate parts of a conventional [[horizontal stabilizer]] (which is fixed) and [[elevator (aeronautics)|elevator]] (which is adjustable). Apart from reduced drag, particularly at high Mach numbers,<ref name="Abzug">{{cite book |last1=Abzug |first1=Malcolm J. |last2=Larrabee |first2=E. Eugene |title=Airplane Stability and Control: A History of the Technologies that Made Aviation Possible |date=23 September 2002 |publisher=Cambridge University Press |isbn=978-1-107-32019-2 |page=78 |url=https://books.google.com/books?id=xaYZBAAAQBAJ |access-date=17 October 2022 |language=en |quote=All-movable tail surfaces became interesting... when high Mach number theory and transonic wind-tunnel tests disclosed poor performance of ordinary flap-type controls.}}</ref> it is a useful device for changing the aircraft balance within wide limits, and for reducing stick forces.<ref>Daroll Stinton, ''The design of the aeroplane'', Control surfaces, p. 447 and 449 : "...for variation of tab size, gear ratio and stabilator pivot position, the stick-free neutral point can be varied almost at will.</ref>

Stabilator is a [[portmanteau]] of ''stabilizer'' and ''elevator''. It is also known as an all-moving [[tailplane]] ([[British English]]), all-movable tail(plane), all-moving stabilizer, all-flying tail ([[American English]]), all-flying horizontal tail, full-flying stabilizer, and slab tailplane.<ref name="Abzug"/>

==General aviation==
[[File:piper.cherokee.pa-28-140.g-bcgj.arp.jpg|thumb|right|Piper Cherokee with stabilator (and anti-servo tab) deflected upwards]]

Because it involves a moving balanced surface, a stabilator can allow the pilot to generate a given pitching moment with a lower control force. Due to the high forces involved in tail balancing loads, stabilators are designed to pivot about their [[aerodynamic center]] (near the tail's mean quarter-chord). This is the point at which the pitching moment is constant regardless of the angle of attack, and thus any movement of the stabilator can be made without added pilot effort. However, to be certified by the appropriate regulatory agency, an airplane must show an increasing resistance to an increasing pilot input (movement).{{citation needed|date=October 2022}} To provide this resistance, stabilators on small aircraft contain an [[servo tab|anti-servo tab]] (usually acting also as a [[trim tab]]) that deflects in the same direction as the stabilator,<ref name="Phillips">{{cite book |last1=Phillips |first1=William Hewitt |title=Journey in Aeronautical Research: A Career at NASA Langley Research Center |date=November 1998 |publisher=NASA History Office |url=https://history.nasa.gov/monograph12/contents.htm |access-date=17 October 2022 |chapter=6. Problems Encountered as a Result of Wartime Developments |quote=the tab on the all-movable tail was changed from a servo tab to a [[anti-servo tab|geared unbalancing tab]]. With this arrangement, the control forces were similar to those on a conventional airplane}}</ref> thus providing an aerodynamic force resisting the pilot's input. General aviation aircraft with stabilators include the [[Piper Cherokee]]<ref name="Abzug"/> and the [[Cessna 177]]. The [[Glaser-Dirks DG-100]] glider initially used a stabilator without an anti-servo tab to increase resistance: as a result, the pitch movement of the glider is very sensitive. Later models used a conventional stabilizer and elevator.

==Military==
[[File:Transonic flow patterns.svg|thumb|right|In transonic flight shock waves form on the upper surface of the wing at a different point from the lower surface. As speed increases, the shock wave moves backwards over the wing. On conventional tails this high pressure causes the elevator to be deflected downwards.]]

All-flying tailplanes were used on many pioneer aircraft and the popular [[Morane-Saulnier G]], [[Morane-Saulnier H|H]] and [[Morane-Saulnier L|L]] monoplanes from France as well as the early [[Fokker Eindecker fighters|Fokker Eindecker]] monoplane and [[Halberstadt D.II]] biplane fighters from Germany all flew with them, although at the cost of [[Aircraft stability|stability]]: none of these aircraft, with the possible exception of the biplane Halberstadts, could be flown hands-off.

Stabilators were developed to achieve adequate [[Pitch (flight)|pitch]] control in supersonic flight, and are almost universal on modern military [[combat aircraft]].<ref name="Abzug"/>

The British wartime [[Miles M.52]] supersonic project was designed with stabilators. Though the design only flew as a scale rocket, its all-flying tail was tested on the [[Miles Falcon]].<ref>Brown, Eric. ''Wings on my Sleeve''. London: Weidenfeld & Nicolson, 2006. {{ISBN|978-0-297-84565-2}}.</ref> The contemporary American supersonic project, the [[Bell X-1]], used separately-adjustable horizontal stabilizer and elevators allowing movement as a single surface or elevator deflection at a fixed tailplane setting.<ref>High Speed Test Flying, Yeager, The Aeronautical Journal, December 1956, p.788</ref>

Entering service in 1951, the [[Boeing B-47 Stratojet]] was the world's first purposely built jet bomber to include one piece stabilator design. A stabilator was considered for the [[Boeing B-52 Stratofortress]] but rejected due to the unreliability of hydraulics at the time.<ref name="Abzug"/>

The [[North American F-86 Sabre]], the first U.S. Air Force aircraft which could go supersonic (although in a shallow dive) was introduced with a conventional horizontal stabilizer with elevators, which was eventually replaced with a stabilator.

When stabilators can move differentially to perform the [[Roll (flight)|roll]] control function of [[ailerons]], as they do on many modern [[fighter aircraft]] they are known as '''elevons''' or '''rolling tails'''. A [[canard (aeronautics)|canard surface]], looking like a stabilator but not stabilizing like a tailplane,<ref>Hoerner, ''Fluid dynamic lift'', about XP-55, p. 11-29, Stability Contributions : "Stabilization in any canard configuration can only be obtained from the wing."</ref> can also be mounted in front of the main [[wing]] in a canard configuration ([[Curtiss-Wright XP-55 Ascender]]).

Stabilators on military aircraft have the same problem of too light control forces (inducing overcontrol) as general aviation aircraft. Unlike light aircraft, supersonic aircraft are not fitted with anti-servo tabs, which would add unacceptable drag. In older jet fighter aircraft, a resisting force was generated within the control system, either by springs or a resisting hydraulic force, rather than by an external anti-servo tab. For example, the [[North American F-100 Super Sabre]], used gearing and a variable stiffness spring attached to the control stick to provide an acceptable resistance to pilot input.<ref>Test Pilot, edited by Schmidt, Mach 2 Books,1997, p.50</ref> In modern fighters, control inputs are processed by computers ("[[fly by wire (flight control)|fly by wire]]"), and there is no direct connection between the pilot's stick and the stabilator.

==Airliners==
[[File:Trimmable horizontal stabiliser.JPG|thumb|Adjustable stabilizer on an [[Embraer E170]], with markings showing the degree of nose-up and nose-down trim available]]

Most modern airliners do not have a stabilator. Instead they have an [[Stabilizer (aeronautics)#Conventional tailplane|adjustable horizontal stabilizer]] and a separate elevator control. The movable horizontal stabilizer is adjusted to keep the pitch axis in [[trim (aircraft)|trim]] during flight as the speed changes, or as fuel is burned and the [[Center of gravity (aircraft)|center of gravity]] moves. These adjustments are commanded by the autopilot when it is engaged, or by the human pilot if the plane is being flown manually. Adjustable stabilizers are not the same as stabilators: a stabilator is controlled by the pilot's control yoke or stick, whereas an adjustable stabilizer is controlled by the trim system.

In the [[Boeing 737]], the adjustable stabilizer trim system is powered by an electrically operated [[jackscrew]].<ref>{{cite book |title=Federal Register |date=July 1978 |publisher=Office of the Federal Register, National Archives and Records Service, General Services Administration |page=32404 |url=https://books.google.com/books?id=mSnOTEFOT2gC |access-date=18 October 2022 |language=en}}</ref>

One example of an airliner with a genuine stabilator used for flight control is the [[Lockheed L-1011]].

==See also==
* [[Canard (aeronautics)|Canard]]
* [[Index of aviation articles]]

==References==
{{reflist}}

==External links==
* [https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/stablator-interacxtive-simulator/ Stabilators (NASA)] – Includes Java applet

{{Aircraft components}}

[[Category:Aerodynamics]]
[[Category:Aircraft controls]]
[[Category:Aircraft wing design]]

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