Stabilizer (aeronautics)

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Vertical and horizontal stabilizer units on an Airbus A380 airliner Tail of a conventional aircraft.svg
Vertical and horizontal stabilizer units on an Airbus A380 airliner

An aircraft stabilizer is an aerodynamic surface, typically including one or more movable control surfaces, [1] [2] 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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In the conventional aircraft configuration, separate vertical (fin) and horizontal (tailplane) stabilizers form an empennage positioned at the tail of the aircraft. Other arrangements of the empennage, such as the V-tail configuration, feature stabilizers which contribute to a combination of longitudinal and directional stabilization and control.

Longitudinal stability and control may be obtained with other wing configurations, including canard, tandem wing and tailless aircraft.

Some types of aircraft are stabilized with electronic flight control; in this case, fixed and movable surfaces located anywhere along the aircraft may serve as active motion dampers or stabilizers.

Horizontal stabilizers

A Boeing 737 uses an adjustable stabilizer, moved by a jackscrew, to provide the required pitch trim forces. Generic stabilizer illustrated. Adjustable stabilizer.svg
A Boeing 737 uses an adjustable stabilizer, moved by a jackscrew, to provide the required pitch trim forces. Generic stabilizer illustrated.

A horizontal stabilizer is used to maintain the aircraft in longitudinal balance, or trim: [3] it exerts a vertical force at a distance so the summation of pitch moments about the center of gravity is zero. [4] The vertical force exerted by the stabilizer varies with flight conditions, in particular according to the aircraft lift coefficient and wing flaps deflection which both affect the position of the center of pressure, and with the position of the aircraft center of gravity (which changes with aircraft loading and fuel consumption). Transonic flight makes special demands on horizontal stabilizers; when the local speed of the air over the wing reaches the speed of sound there is a sudden move aft of the center of pressure.

Another role of a horizontal stabilizer is to provide longitudinal static stability. Stability can be defined only when the vehicle is in trim; [5] it refers to the tendency of the aircraft to return to the trimmed condition if it is disturbed. [6] This maintains a constant aircraft attitude, with unchanging pitch angle relative to the airstream, without active input from the pilot. Ensuring static stability of an aircraft with a conventional wing requires that the aircraft center of gravity be ahead of the center of pressure, so a stabilizer positioned at the rear of the aircraft will produce lift in the downwards direction.

The elevator serves to control the pitch axis; in case of a fully movable tail, the entire assembly acts as a control surface.

Wing-stabilizer interaction

The upwash and downwash associated with the generation of lift is the source of aerodynamic interaction between the wing and stabilizer, which translates into a change in the effective angle of attack for each surface. The influence of the wing on a tail is much more significant than the opposite effect and can be modeled using the Prandtl lifting-line theory; however, an accurate estimation of the interaction between multiple surfaces requires computer simulations or wind tunnel tests. [7]

Horizontal stabilizer configurations

Conventional tailplane

The adjustable horizontal stabilizer of an Embraer 170, with markings showing nose-up and nose-down trim angles Trimmable horizontal stabiliser.JPG
The adjustable horizontal stabilizer of an Embraer 170, with markings showing nose-up and nose-down trim angles

In the conventional configuration the horizontal stabilizer is a small horizontal tail or tailplane located to the rear of the aircraft. This is the most common configuration.

On many aircraft, the tailplane assembly consists of a fixed surface fitted with a hinged aft elevator surface. Trim tabs may be used to relieve pilot input forces; conversely in some cases, such as small aircraft with all-moving stabilizers, anti-servo tabs are used to increase these forces.

Most airliners and transport aircraft feature a large, slow-moving trimmable tail plane which is combined with independently-moving elevators. The elevators are controlled by the pilot or autopilot and primarily serve to change the aircraft's attitude, while the whole assembly is used to trim (maintaining horizontal static equilibrium) and stabilize the aircraft in the pitch axis.

Many supersonic aircraft feature an all-moving tail assembly, also named stabilator, where the entire surface is adjustable. [8]

Variants on the conventional configuration include the T-tail, Cruciform tail, Twin tail and Twin-boom mounted tail.

Three-surface aircraft

The three-surface configuration of the Piaggio P-180 Avanti Piaggio P-180 Avanti Rennes 2010.jpg
The three-surface configuration of the Piaggio P-180 Avanti

Three-surface aircraft such as the Piaggio P.180 Avanti or the Scaled Composites Triumph and Catbird, the tailplane is a stabilizer as in conventional aircraft; the frontplane, called foreplane or canard, provides lift and serves as a balancing surface.

Some earlier three-surface aircraft, such as the Curtiss AEA June Bug or the Voisin 1907 biplane, were of conventional layout with an additional front pitch control surface which was called "elevator" or sometimes "stabilisateur". [9] Lacking elevators, the tailplanes of these aircraft were not what is now called conventional stabilizers. For example, the Voisin was a tandem-lifting layout (main wing and rear wing) with a foreplane that was neither stabilizing nor mainly lifting; it was called an "équilibreur" ("balancer"), [10] and used as a pitch control and trim surface.

Canard aircraft

The canard configuration of the Beechcraft Starship NASA-2000Starship.jpg
The canard configuration of the Beechcraft Starship

In the canard configuration, a small wing, or foreplane, is located in front of the main wing. Some authors call it a stabilizer [11] [12] [13] [14] or give to the foreplane alone a stabilizing role, [15] although as far as pitch stability is concerned, a foreplane is generally described as a destabilizing surface, [16] the main wing providing the stabilizing moment in pitch. [17] [18] [19]

In naturally unstable aircraft, the canard surfaces may be used as an active part of the artificial stability system, and are sometimes named horizontal stabilizers. [20]

Tailless aircraft

The tailless configuration of Concorde Concorde on Bristol.jpg
The tailless configuration of Concorde

Tailless aircraft lack a separate horizontal stabilizer. In a tailless aircraft, the horizontal stabilizing surface is part of the main wing. [21] [22] Longitudinal stability in tailless aircraft is achieved by designing the aircraft so that its aerodynamic center is behind the center of gravity. This is generally done by modifying the wing design, for example by varying the angle of incidence in the span-wise direction (wing washout or twist), or by using reflexed camber airfoils.

Vertical stabilizers

A vertical stabilizer provides directional (or yaw) stability and usually comprises a fixed fin and movable control rudder hinged to its rear edge. [23] Less commonly, there is no hinge and the whole fin surface is pivoted for both stability and control. [24]

When an aircraft encounters a horizontal gust of wind, yaw stability causes the aircraft to turn into the wind, rather than turn in the same direction. [25]

Fuselage geometry, engine nacelles and rotating propellers all influence lateral static stability and affect the required size of the stabilizer. [26]

Not all aircraft have a vertical stabilizer. Instead wing sweep and dihedral can provide a similar degree of directional stability, while directional control is often effected by adding drag on the side of the aircraft the aircraft is to be turned towards, either in the form of spoilers or split ailerons.

Tailless directional stabilization and control

Although the use of a vertical stabilizer is most common, it is possible to obtain directional stability with no discrete vertical stabilizer. This occurs when the wing is swept back and in some cases, as for example on the Rogallo wing often used for hang gliders, means that no fin is needed.

Combined longitudinal - directional stabilizers

The Beechcraft Bonanza, the most common example of V-tail empennage configuration V-Tailed Beechcraft Bonanza.jpg
The Beechcraft Bonanza, the most common example of V-tail empennage configuration

On some aircraft, horizontal and vertical stabilizers are combined in a pair of surfaces named V-tail. In this arrangement, two stabilizers (fins and rudders) are mounted at 90 - 120° to each other, [note 1] giving a larger horizontal projected area than vertical one as in the majority of conventional tails. The moving control surfaces are then named ruddervators. [28] [note 2] The V-tail thus acts both as a yaw and pitch stabilizer.

Although it may seem that the V-tail configuration can result in a significant reduction of the tail wetted area, it suffers from an increase in control-actuation complexity, [28] as well as complex and detrimental aerodynamic interaction between the two surfaces. [29] This often results in an upsizing in the total area that reduces or negates the original benefit. [28] The Beechcraft Bonanza light aircraft was originally designed with a V-tail.

Others combined layouts exist. The General Atomics MQ-1 Predator unmanned aircraft has an inverted V-tail. The tail surfaces of the Lockheed XFV could be described as a V-tail with surfaces that extended through the fuselage to the opposite side. The LearAvia Lear Fan had a Y-tail. All twin tail arrangements with a tail dihedral angle will provide a combination of longitudinal and directional stabilization.

Notes

  1. ↑ F-117 Nighthawk, 90° - Fouga Magister, 105° - Beech Bonanza, 116°
  2. ↑ A portmanteau of rudder & elevator

Related Research Articles

Tailplane

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.

Delta wing 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).

Flying wing

A flying wing is a tailless fixed-wing aircraft that has no definite fuselage, with its crew, payload, fuel, and equipment housed inside the main wing structure. A flying wing may have various small protuberances such as pods, nacelles, blisters, booms, or vertical stabilizers.

Flight control surfaces 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.

Northrop X-4 Bantam Experimental small twin jet airplane

The Northrop X-4 Bantam was a prototype small twinjet aircraft manufactured by Northrop Corporation in 1948. It had no horizontal tail surfaces, depending instead on combined elevator and aileron control surfaces for control in pitch and roll attitudes, almost exactly in the manner of the similar-format, rocket-powered Messerschmitt Me 163 of Nazi Germany's Luftwaffe. Some aerodynamicists had proposed that eliminating the horizontal tail would also do away with stability problems at fast speeds resulting from the interaction of supersonic shock waves from the wings and the horizontal stabilizers. The idea had merit, but the flight control systems of that time prevented the X-4 from achieving any success.

Elevator (aeronautics)

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.

Stabilator

A stabilator, more frequently all-moving tail or all-flying tail, is a fully movable aircraft 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 a higher efficiency at high Mach number, it is a useful device for changing the aircraft balance within wide limits, and for mastering the stick forces.

Empennage 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.

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".

The United States Air Force Stability and Control Digital DATCOM is a computer program that implements the methods contained in the USAF Stability and Control DATCOM to calculate the static stability, control and dynamic derivative characteristics of fixed-wing aircraft. Digital DATCOM requires an input file containing a geometric description of an aircraft, and outputs its corresponding dimensionless stability derivatives according to the specified flight conditions. The values obtained can be used to calculate meaningful aspects of flight dynamics.

Vertical stabilizer

A vertical stabilizer, vertical stabiliser, or fin, is a structure designed to reduce aerodynamic side slip and provide directional stability. They are most commonly found on vehicles such as aircraft or cars. It is analogous to a skeg on boats and ships. Other objects such as missiles or bombs utilize them too. They are typically found on the aft end of the fuselage or body.

Mach tuck 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.

Canard (aeronautics)

A canard is an aeronautical arrangement wherein a small forewing or foreplane is placed forward of the main wing of a fixed-wing aircraft. The term "canard" may be used to describe the aircraft itself, the wing configuration, or the foreplane.

If an aircraft in flight suffers a disturbance in pitch that causes an increase in angle of attack, it is desirable that the aerodynamic forces on the aircraft cause a decrease in angle of attack so that the disturbance does not cause a continuous increase in angle of attack. This is longitudinal static stability.

Tailless aircraft

A tailless aircraft has no tail assembly and no other horizontal surface besides its main wing. The aerodynamic control and stabilisation functions in both pitch and roll are incorporated into the main wing. A tailless type may still have a conventional vertical fin and rudder.

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

Wing configuration 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.

Three-surface aircraft

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.

Chine (aeronautics)

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.

Outboard tail

An outboard tail is a type of aircraft tail or empennage which is split in two, with each half mounted on a short boom just behind and outboard of each wing tip. It comprises outboard horizontal stabilizers (OHS) and may or may not include additional boom-mounted vertical stabilizers (fins). OHS designs are sometimes described as a form of tailless aircraft.

References

  1. ↑ Empennage - D. Stinton The design of the aeroplane, Longitudinal stability - Hoerner Fluid Dynamic Lift - Ilan Kroo, Aircraft Design. In stability considerations (tail sizing, tail area, stabiliser volume coefficient), authors always deal with the whole unit, that includes elevators. "Horizontal tail" or "tail" terms are generally used in lieu of "stabilizer".
  2. ↑ Roskam, Jan (2002). Airplane Design: Pt. 3. Lawrence: DARcorporation. p. 287. ISBN   1-884885-56-X . Retrieved 30 July 2015.
  3. ↑ Daroll Stinton, The design of the aeroplane, "Longitudinal balance (trim)".
  4. ↑ Phillips, Warren F. (2010). "4.1 Fundamentals of Static Equilibrium and Stability". Mechanics of Flight (2nd ed.). Hoboken, New Jersey: Wiley & Sons. p. 377. ISBN   978-0-470-53975-0. When the controls are set so that the resultant forces and the moments about the center of gravity are all zero, the aircraft is said to be in trim, which simply means static equilibrium
  5. ↑ W.H. Phillips, A Career at NASA Langley Research Center, Chap.4, Flying Qualities
  6. ↑ Phillips, Warren F. (2010). "4.2 Pitch Stability of a Cambered Wing". Mechanics of Flight (2nd ed.). Hoboken, New Jersey: Wiley & Sons. p. 381. ISBN   978-0-470-53975-0. For an airplane to be statically stable in rotation, any disturbances in roll, pitch or yaw must all result in the production of a restoring moment that will return the aircraft to the original equilibrium state.
  7. ↑ Phillips, Warren F. (2010). "4.3 Simplified Pitch Stability Analysis for a Wing-Tail Combination". Mechanics of Flight (2nd ed.). Hoboken, New Jersey: Wiley & Sons. p. 391. ISBN   978-0-470-53975-0.
  8. ↑ "Horizontal stabilizer - elevator", The Beginner's Guide to Aeronautics, NASA Glenn Research Center, Sep 13, 2010
  9. ↑ Gérard Hartmann (12 May 2003), "Les hydros Farman" (PDF), Dossiers historiques et technique aéronautique française, le stabilisateur avant sera supprimé en cours d'année ("the front stabilizer will be removed during the year")
  10. ↑ Gabriel Voisin, Mes 10.000 cerfs-volants (My 10,000 kites), page 166: "et je m'apprêtais à tirer sur mon équilibreur... puis il braqua son équilibreur vers la montée."
  11. ↑ Garrison, P; "Three's Company"; Flying129 (12), December 2002, pp.85-86: "the stabilizer in the front" ... "This is the function of the stabilizer. if it's in the back it typically pushes downward, and if it's in the front it lifts upward."
  12. ↑ Benson, T (Ed): "Airplane parts and functions", Beginner's Guide to Aeronautics, NASA Glenn Research Center, On the Wright brother's first aircraft, the horizontal stabilizer was placed in front of the wings.
  13. ↑ US Patent US 6064923 A, Aircraft with reduced wing structure loading: "...a front stabilizer, generally known as a canard stabilizer,"
  14. ↑ "Parts of Airplane", The Beginner's Guide to Aeronautics, NASA Glenn Research Center
  15. ↑ Horizontal stabilizer - elevator, NASA, On some aircraft, the pitch stability and control is provided by a horizontal surface placed forward of the center of gravity
  16. ↑ e.g. In AIR International May 1999, p.311, Hoerner and Borst, Fluid Dynamic Lift, page 11-29, and Page 11-33 Delta canard, NASA TM 88354, A look at handling qualities of canard configurations, p. 14 and Kundu, Aircraft Design, Page 92,
  17. ↑ Phillips, Warren F. (2010). "4.6 Simplified Pitch Stability Analysis for a Wing-Canard Combination". Mechanics of Flight (2nd ed.). Hoboken, New Jersey: Wiley & Sons. p. 425. ISBN   978-0-470-53975-0. …it is the main wing and not the canard that provides stability for the wing-canard configuration.
  18. ↑ AIAA/AHS/ASEE Aircraft Design, Systems and Operations Meeting: ... - Volume 2 - Page 309, "Pitching-moment results show the stabilising effect of the wing and the destabilizing effect of the canard."
  19. ↑ F.H. Nichols,The Effects of Wing Vertical Location and Vertical-tail Arrangement on the Stability Characteristics of Canard Airplane Configurations, page 9, "The body also produces a substantial destabilizing component which is adequately balanced by the large stabilizing effect of the wing."
  20. ↑ The X-29 ... while its canards — horizontal stabilizers to control pitch — were in front of the wings instead of on the tail"
  21. ↑ Theory and Practice of Using Flying Wings, Apogee Components
  22. ↑ Notes on the stability and control of tailless airplanes, Jones, Robert, naca-tn-837, 1941
  23. ↑ Daroll Stinton, The design of the aeroplane, lateral and directional stability and spinning
  24. ↑ Barnard, R.H.; Philpott, D.R. (2010). "10. Aircraft control". Aircraft Flight (4th ed.). Harlow, England: Prentice Hall. p.  271. ISBN   978-0-273-73098-9.
  25. ↑ Barber, Horatio, "Chapter II - Stability and Control", The Aeroplane Speaks, Electronic Text Center, University of Virginia Library
  26. ↑ Phillips, Warren F. (2010). "5 Lateral Static Stability and Trim". Mechanics of Flight (2nd ed.). Hoboken, New Jersey: Wiley & Sons. ISBN   978-0-470-53975-0.
  27. ↑ Sweetman, Bill (2005). Lockheed Stealth. North Branch, Minnesota: Zenith Imprint. p. 73. ISBN   0-7603-1940-5.
  28. 1 2 3 Raymer, Daniel P. (1999). "4.5 Tail Geometry and Arrangement". Aircraft Design: A Conceptual Approach (3rd ed.). Reston, Virginia: American Institute of Aeronautics and Astronautics. p.  78. ISBN   1-56347-281-3.
  29. ↑ Phillips, Warren F. (2010). "5.5 Effects of Tail Dihedral on Yaw Stability". Mechanics of Flight (2nd ed.). Hoboken, New Jersey: Wiley & Sons. p. 533. ISBN   978-0-470-53975-0.
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