Tailplane

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The horizontal stabilizer is the fixed horizontal surface of the empennage Empennage components FAA GFH.svg
The horizontal stabilizer is the fixed horizontal surface of the empennage

A tailplane, also known as a horizontal stabiliser, is a small lifting surface located on the tail (empennage) behind the main lifting surfaces of a fixed-wing aircraft as well as other non-fixed-wing aircraft such as helicopters and gyroplanes. Not all fixed-wing aircraft have tailplanes. Canards, tailless and flying wing aircraft have no separate tailplane, while in V-tail aircraft the vertical stabiliser, rudder, and the tail-plane and elevator are combined to form two diagonal surfaces in a V layout.

Contents

The function of the tailplane is to provide stability and control. In particular, the tailplane helps adjust for changes in position of the centre of pressure or centre of gravity caused by changes in speed and attitude, fuel consumption, or dropping cargo or payload.

Tailplane types

The tailplane comprises the tail-mounted fixed horizontal stabiliser and movable elevator. Besides its planform, it is characterised by:

Some locations have been given special names:

Tail fuselage mounted.svg
Fuselage mounted
Tail cruciform.svg
Cruciform
Tail T.svg
T-tail
Tail plane flying.svg
Flying tailplane

Stability

Tailplane (in shadow) of an easyJet Airbus A319 Tailplane.JPG
Tailplane (in shadow) of an easyJet Airbus A319

A wing with a conventional aerofoil profile makes a negative contribution to longitudinal stability. This means that any disturbance (such as a gust) which raises the nose produces a nose-up pitching moment which tends to raise the nose further. With the same disturbance, the presence of a tailplane produces a restoring nose-down pitching moment, which may counteract the natural instability of the wing and make the aircraft longitudinally stable (in much the same way a weather vane always points into the wind).

The longitudinal stability of an aircraft may change when it is flown "hands-off"; i.e. when the flight controls are subject to aerodynamic forces but not pilot input forces.

Damping

In addition to giving a restoring force (which on its own would cause oscillatory motion) a tailplane gives damping. This is caused by the relative wind seen by the tail as the aircraft rotates around the centre of gravity. For example, when the aircraft is oscillating, but is momentarily aligned with the overall vehicle's motion, the tailplane still sees a relative wind that is opposing the oscillation.

Lift

Depending on the aircraft design and flight regime, its tailplane may create positive lift or negative lift (downforce). It is sometimes assumed that on a stable aircraft this will always be a net down force, but this is untrue. [2]

On some pioneer designs, such as the Bleriot XI, the centre of gravity was between the neutral point and the tailplane, which also provided positive lift. However this arrangement can be unstable and these designs often had severe handling issues. The requirements for stability were not understood until shortly before World War I – the era within which the British Bristol Scout light biplane was designed for civilian use, with an airfoiled lifting tail throughout its production run into the early World War I years and British military service from 1914 to 1916 – when it was realised that moving the centre of gravity further forwards allowed the use of a non-lifting tailplane in which the lift is nominally neither positive nor negative but zero, which leads to more stable behaviour. [3] Later examples of aircraft from World War I and onwards into the interwar years that had positive lift tailplanes include, chronologically, the Sopwith Camel, Charles Lindbergh's Spirit of St. Louis, the Gee Bee Model R Racer - all aircraft with a reputation for being difficult to fly, and the easier-to-fly Fleet Finch two-seat Canadian trainer biplane, itself possessing a flat-bottom airfoiled tailplane unit not unlike the earlier Bristol Scout. But with care a lifting tailplane can be made stable. An example is provided by the Bachem Ba 349 Natter VTOL rocket-powered interceptor, which had a lifting tail and was both stable and controllable in flight. [4]

Some aircraft and flight modes can require the tailplane to generate substantial downforce. This is particularly so when flying slowly and at a high angle of attack (AoA). On some types, the demand in this flight mode has been so extreme that it has caused the tailplane to stall. On the Gloster Meteor T.7 a stall could be triggered by turbulence when the airbrakes were deployed. On the McDonnell Douglas F-4 Phantom II it initially occurred during takeoff and landing approach, and leading-edge slats were fitted to the tailplane upside-down in order to maintain smooth airflow and downforce "lift" at high AoA. The Pilatus P-3 trainer required a ventral keel to cure a similar effect when spun, while the McDonnell Douglas T-45 Goshawk suffered excess downwash from the wing when the flaps were deployed, necessitating a small "SMURF" surface fixed to the fuselage, such that it aligned with the stabilizer leading-edge root at the critical angle. [5]

Active stability

Using a computer to control the elevator allows aerodynamically unstable aircraft to be flown in the same manner.

Aircraft such as the F-16 are flown with artificial stability. The advantage of this is a significant reduction in drag caused by the tailplane, and improved maneuverability.

Mach tuck

At transonic speeds, an aircraft can experience a shift rearwards in the center of pressure due to the buildup and movement of shockwaves. This causes a nose-down pitching moment called Mach tuck. Significant trim force may be needed to maintain equilibrium, and this is most often provided using the whole tailplane in the form of an all-flying tailplane or stabilator.

Control

A tailplane usually has some means allowing the pilot to control the amount of lift produced by the tailplane. This in turn causes a nose-up or nose-down pitching moment on the aircraft, which is used to control the aircraft in pitch.

Elevator: A conventional tailplane normally has a hinged aft surface called an elevator,

Stabilator or all-moving tail: In transonic flight shock waves generated by the front of the tailplane render any elevator unusable. An all-moving tail was developed by the British for the Miles M.52, but first saw actual transonic flight on the Bell X-1; Bell Aircraft Corporation had included an elevator trim device that could alter the angle of attack of the entire tailplane. This saved the program from a costly and time-consuming rebuild of the aircraft.[ citation needed ]

Transonic and supersonic aircraft now have all-moving tailplanes to counteract Mach tuck and maintain maneuverability when flying faster than the critical Mach number. Normally called a stabilator, this configuration is often referred to as an "all-moving" or "all-flying" tailplane.

See also

Related Research Articles

<span class="mw-page-title-main">Stall (fluid dynamics)</span> Abrupt reduction in lift due to flow separation

In fluid dynamics, a stall is a reduction in the lift coefficient generated by a foil as angle of attack increases. This occurs when the critical angle of attack of the foil is exceeded. The critical angle of attack is typically about 15°, but it may vary significantly depending on the fluid, foil, and Reynolds number.

<span class="mw-page-title-main">Delta wing</span> Triangle shaped aircraft wing configuration

A delta wing is a wing shaped in the form of a triangle. It is named for its similarity in shape to the Greek uppercase letter delta (Δ).

<span class="mw-page-title-main">Flight control surfaces</span> Surface that allows a pilot to adjust and control an aircrafts flight attitude

Aircraft flight control surfaces are aerodynamic devices allowing a pilot to adjust and control the aircraft's flight attitude.

<span class="mw-page-title-main">Dihedral (aeronautics)</span> Angle between each wing or tail surface within a pair

In aeronautics, dihedral is the angle between the left and right wings of an aircraft. "Dihedral" is also used to describe the effect of sideslip on the rolling of the aircraft.

<span class="mw-page-title-main">Elevator (aeronautics)</span> Aircraft control surface used to control pitch

Elevators are flight control surfaces, usually at the rear of an aircraft, which control the aircraft's pitch, and therefore the angle of attack and the lift of the wing. The elevators are usually hinged to the tailplane or horizontal stabilizer. They may be the only pitch control surface present, and are sometimes located at the front of the aircraft or integrated into a rear "all-moving tailplane", also called a slab elevator or stabilator.

<span class="mw-page-title-main">Stabilator</span>

A stabilator is a fully movable aircraft horizontal stabilizer. It serves the usual functions of longitudinal stability, control and stick force requirements otherwise performed by the separate parts of a conventional horizontal stabilizer and elevator. Apart from reduced drag, particularly at high Mach numbers, it is a useful device for changing the aircraft balance within wide limits, and for reducing stick forces.

<span class="mw-page-title-main">Empennage</span> Tail section of an aircraft containing stabilizers

The empennage, also known as the tail or tail assembly, is a structure at the rear of an aircraft that provides stability during flight, in a way similar to the feathers on an arrow. The term derives from the French language verb empenner which means "to feather an arrow". Most aircraft feature an empennage incorporating vertical and horizontal stabilising surfaces which stabilise the flight dynamics of yaw and pitch, as well as housing control surfaces.

Aircraft flight mechanics are relevant to fixed wing and rotary wing (helicopters) aircraft. An aeroplane, is defined in ICAO Document 9110 as, "a power-driven heavier than air aircraft, deriving its lift chiefly from aerodynamic reactions on surface which remain fixed under given conditions of flight".

<span class="mw-page-title-main">Vertical stabilizer</span> Aircraft component

A vertical stabilizer or tail fin is the static part of the vertical tail of an aircraft. The term is commonly applied to the assembly of both this fixed surface and one or more movable rudders hinged to it. Their role is to provide control, stability and trim in yaw. It is part of the aircraft empennage, specifically of its stabilizers.

<span class="mw-page-title-main">Mach tuck</span> Aerodynamic effect

Mach tuck is an aerodynamic effect whereby the nose of an aircraft tends to pitch downward as the airflow around the wing reaches supersonic speeds. This diving tendency is also known as tuck under. The aircraft will first experience this effect at significantly below Mach 1.

<span class="mw-page-title-main">Tandem wing</span>

A tandem wing is a wing configuration in which a flying craft or animal has two or more sets of wings set one behind another. All the wings contribute to lift.

<span class="mw-page-title-main">Stabilizer (aeronautics)</span> Aircraft component

An aircraft stabilizer is an aerodynamic surface, typically including one or more movable control surfaces, that provides longitudinal (pitch) and/or directional (yaw) stability and control. A stabilizer can feature a fixed or adjustable structure on which any movable control surfaces are hinged, or it can itself be a fully movable surface such as a stabilator. Depending on the context, "stabilizer" may sometimes describe only the front part of the overall surface.

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An aircraft in flight is free to rotate in three dimensions: yaw, nose left or right about an axis running up and down; pitch, nose up or down about an axis running from wing to wing; and roll, rotation about an axis running from nose to tail. The axes are alternatively designated as vertical, lateral, and longitudinal respectively. These axes move with the vehicle and rotate relative to the Earth along with the craft. These definitions were analogously applied to spacecraft when the first crewed spacecraft were designed in the late 1950s.

<span class="mw-page-title-main">Canard (aeronautics)</span> Aircraft configuration in which a small wing is placed in front of the main wing

In aeronautics, a canard is a wing configuration in which a small forewing or foreplane is placed forward of the main wing of a fixed-wing aircraft or a weapon. The term "canard" may be used to describe the aircraft itself, the wing configuration, or the foreplane. Canard wings are also extensively used in guided missiles and smart bombs.

<span class="mw-page-title-main">Tailless aircraft</span> Aircraft whose only horizontal aerodynamic surface is its main wing

In aeronautics, a tailless aircraft is an aircraft with no other horizontal aerodynamic surface besides its main wing. It may still have a fuselage, vertical tail fin, and/or vertical rudder.

In flight dynamics, longitudinal stability is the stability of an aircraft in the longitudinal, or pitching, plane. This characteristic is important in determining whether an aircraft pilot will be able to control the aircraft in the pitching plane without requiring excessive attention or excessive strength.

<span class="mw-page-title-main">Wing configuration</span> Describes the general shape and layout of an aircraft wing

The wing configuration of a fixed-wing aircraft is its arrangement of lifting and related surfaces.

<span class="mw-page-title-main">Three-surface aircraft</span> Fixed-wing aircraft with a main central wing plus fore and aft surfaces

A three-surface aircraft or sometimes three-lifting-surface aircraft has a foreplane, a central wing and a tailplane. The central wing surface always provides lift and is usually the largest, while the functions of the fore and aft planes may vary between types and may include lift, control and/or stability.

<span class="mw-page-title-main">Chine (aeronautics)</span> Sharp angle in aircraft cross-sections used as control surface

In aircraft design, a chine is a longitudinal line of sharp change in the cross-section profile of the fuselage or similar body. The term chine originates in boatbuilding, where it applies to a sharp profile change in the hull of a boat. In a flying boat hull or floatplane float, the longitudinal line of sharp change in cross-section where the bottom plane meets the sidewall is an example of a chine.

<span class="mw-page-title-main">Dunne-Huntington triplane</span> Type of aircraft

The Dunne-Huntington triplane, sometimes referred to as a biplane, was a pioneer aircraft designed by J. W. Dunne and built by A. K. Huntington. It was of unusual staggered triple-tandem configuration and an early example of an inherently stable aeroplane, flying regularly between 1910 and 1914.

References

  1. Anderson, John D., Introduction to Flight, 5th ed, p 517
  2. Burns, BRA (23 February 1985), "Canards: Design with Care", Flight International, pp. 19–21, It is a misconception that tailed aeroplanes always carry tailplane downloads. They usually do, with flaps down and at forward c.g. positions, but with flaps up at the c.g. aft, tail loads at high lift are frequently positive (up), although the tail's maximum lifting capability is rarely approached..p.19 p.20 p.21
  3. Answers to correspondents, Flight, 2 November 1916, Page 962; "A "lifting tail" is one which normally carries a certain amount of load, and which is therefore often cambered in order to make it more efficient. For instance, the tail planes of the old Farman biplanes were "lifting tail planes," and were, as a matter of fact, rather heavily cambered. By a non-lifting tail plane is meant one which does not, in the normal flying attitude, carry any portion of the load, but is merely "floating." This type of plane is usually, although not invariably, made of symmetrical section – i.e., it is either a perfectly flat plane, built up of a framework of steel tubes, or it is constructed of spars and ribs after the fashion of the main planes, but symmetrical in section and convex on both sides. The object of the latter form of section is, of course, to provide a good "streamline" shape which will offer a minimum of resistance. During flight it constantly occurs that such a tail plane is momentarily loaded, the load being either upwards or downwards according to circumstances, and then, of course, the tail plane is no longer, strictly speaking, " non-lifting." ... a non-lifting tail plane is not invariably symmetrical in section. Some designers favour a section in which the upper surface is convex, while the lower surface is perfectly flat. The reasons usually advanced for the employment of such a section are that, as the tail planes may – and, indeed, frequently do – work in the down draught from the main planes, a tail plane set parallel to the path of the machine, or, in other words, parallel to the propeller shaft, is virtually subject to a load acting in a downward direction. Now, an unsymmetrical tail plane like that referred to above is still giving a certain amount of lift a to angle of incidence, whereas the symmetrical .section would, of course, give no lift when the incidence was zero. The plano-convex section therefore tends, owing to the slight lift at no angle of incidence, to counteract the effect of the down draught from the wings, and may therefore be said to be equivalent to a flat or streamline plane set at a slight angle to the propeller shaft. The tail plane of the B.E.2C, as is the case on the majority of modern machines, is of the non-lifting type."
  4. Green, W.; Warplanes of the Third Reich, Macdonald and Jane's, 1970.
  5. Oakey, Mick; "Out of the Blue", The Aviation Historian , No. 1, 2012, pp.109-113.