NationMaster - Encyclopedia: Airfoil

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For the kite, see foil kite.

Various components of the airfoil.

An airfoil (in American English, or aerofoil in British English) is the shape of a wing or blade (of a propeller, rotor or turbine) or sail as seen in cross-section. Foil kites are soft kites. ... Image File history File links Airfoil. ... Image File history File links Airfoil. ... For other uses, see American English (disambiguation). ... British English (BrE, BE, en-GB) is the broad term used to distinguish the forms of the English language used in the United Kingdom from forms used elsewhere in the Anglophone world. ... For other uses, see Wing (disambiguation). ... For other uses, see Propeller (disambiguation). ... A rotor is the rotating part of a helicopter which generates lift, either vertically in the case of a main rotor, or horizontally in the case of a tail rotor. ... A Siemens steam turbine with the case opened. ... A gaff-rigged cutter flying a mainsail, staysail and genoa jib For other uses, see Sail (disambiguation). ...

An airfoil shaped body moved through a fluid produces a force perpendicular to the motion called lift. Subsonic flight airfoils have a characteristic shape with a rounded leading edge, followed by a sharp trailing edge, often with asymmetric camber. Airfoils designed with water as the working fluid are also called hydrofoils. A fluid is defined as a substance that continually deforms (flows) under an applied shear stress regardless of the magnitude of the applied stress. ... The lift force, lifting force or simply lift is a mechanical force generated by solid objects as they move through a fluid. ... This article does not cite its references or sources. ... The camber in aerospace engineering is the asymmetry between the top and the bottom curves of an airfoil. ...

1 Introduction
2 Aerofoil terminology
3 Thin Airfoil Theory
4 Reference (thin airfoil/aerofoil theory)
5 See also
6 External links
7 References

Introduction

The historical evolution of airfoil sections, 1908 - 1944, NASA

Lift and Drag curves for a typical airfoil

A fixed-wing aircraft's wings, horizontal, and vertical stabilizers are built with airfoil-shaped cross sections, as are helicopter rotor blades. Airfoils are also found in propellers, fans, compressors and turbines. Sails are also airfoils, and the underwater surfaces of sailboats, such as the centerboard, and keel are similar in cross-section and operate on the same principles as airfoils. Swimming and flying creatures and even many plants and sessile organisms employ airfoils; common examples being bird wings, the bodies of fishes, and the shape of sand dollars. An airfoil shaped wing can create downforce on an automobile or other motor vehicle, improving traction. Image File history File links This is a lossless scalable vector image. ... Image File history File links This is a lossless scalable vector image. ... This article is about evolution in biology. ... This article is about the American space agency. ... Image File history File links Download high resolution version (1000x750, 62 KB)Note: For a Clark-Y airfoil the geometrical reference for angle of attack is the flat lower surface. ... Image File history File links Download high resolution version (1000x750, 62 KB)Note: For a Clark-Y airfoil the geometrical reference for angle of attack is the flat lower surface. ... Airplane and Aeroplane redirect here. ... For other uses, see Wing (disambiguation). ... The tail of a Lufthansa airliner (Airbus A319) in flight, showing the horizontal and vertical stabilizer Mathematics: see Group action. ... The vertical stabilizer or fin of an aircraft is found on its tail, generally pointing straight upward. ... For other uses, see Helicopter (disambiguation). ... For other uses, see Propeller (disambiguation). ... Household Electric Fan A mechanical fan is a device used to produce an airflow for the purpose of creature comfort, ventilation, exhaust, or any other gaseous transport. ... This article does not cite any references or sources. ... A Siemens steam turbine with the case opened. ... A gaff-rigged cutter flying a mainsail, staysail and genoa jib For other uses, see Sail (disambiguation). ... A centreboard is a form of removable keel on a small sailing boat or dinghy which can be removed to lower the draught (or depth) of the vessel. ... For other uses, see Keel (disambiguation). ... Look up sessile in Wiktionary, the free dictionary. ... Suborders Laganina Rotulina Scutellina Sand dollars are in the Echinoid (Echinoderms) class of marine animals. ... Three different styles of front wings from three different Formula 1 eras, all designed to produce downforce on the front wheels. ... â€œCarâ€ and â€œCarsâ€ redirect here. ... Traction usually refers to friction between a drive member and the surface it runs on, where friction is used to provide motion. ...

While any object with an angle of attack in a moving fluid, such as a flat plate, a building, or the deck of a bridge, will generate an aerodynamic force perpendicular to the flow called lift, airfoils are more efficient lifting shapes, able generate more lift (up to a point), and to generate lift with less drag. In this diagram, the black arrow represents the direction of the wind. ... The lift force, lifting force or simply lift is a mechanical force generated by solid objects as they move through a fluid. ... Look up Drag in Wiktionary, the free dictionary. ...

A lift and drag curve obtained in wind tunnel testing is shown on the right. The curve represents an airfoil with a positive camber so lift is produced at zero angle of attack. With increased angle of attack, lift increases in a roughly linear relation. At about eighteen degrees this airfoil stalls and lift falls off quickly beyond that. Drag is least at a slight negative angle for this particular airfoil, and increases rapidly with higher angles. NASA wind tunnel with the model of a plane A wind tunnel is a research tool developed to assist with studying the effects of air moving over or around solid objects. ... Camber may refer to: Camber, East Sussex, a seaside resort in England, near to Camber Sands. ...

Airfoil design is a major facet of aerodynamics. Various airfoils serve different flight regimes. Asymmetric airfoils can generate lift at zero angle of attack, while a symmetric airfoil may better suit frequent inverted flight as in an aerobatic airplane. Supersonic airfoils are much more angular in shape and can have a very sharp leading edge. A supercritical airfoil, with its low camber, reduces transonic drag divergence. Movable high-lift devices, flaps and slats are fitted to airfoils on many aircraft. This article does not cite any references or sources. ... Soon after aircraft were invented, pilots realised that they could be used as part of a flying circus to entertain people or impress others in what was termed aerobatics. ... A Supercritical airfoil is an airfoil designed, primarily, to delay the onset of wave drag in the transonic speed range. ... Transonic is an aeronautics term referring to a range of velocities just below and above the speed of sound. ... Flaps are hinged surfaces on the trailing edge of an airplane wing which, when deployed, increase the lift (and drag) of a wing by changing the camber of the airfoil. ... Slats are small aerodynamic surfaces on the leading edge of an airplane wing which, when deployed, allow the wing to operate at a higher angle of attack. ...

Schemes have been devised to describe airfoils — an example is the NACA system. Various ad-hoc naming systems are also used. An example of a general purpose airfoil that finds wide application, and predates the NACA system, is the Clark-Y. Today, airfoils are designed for specific functions using inverse design programs such as PROFIL and XFOIL. Modern aircraft wings may have different airfoil sections along the wing span, each one optimized for the conditions in each section of the wing. The NACA airfoils are airfoil shapes for aircraft wings developed by the National Advisory Committee for Aeronautics (NACA). ... Clark-Y is the name of a particular aerofoil profile, widely used in general purpose aircraft designs, and much studied in aerodynamics over the years. ...

An airfoil designed for winglets (PSU 90-125WL)

Image File history File links Size of this preview: 800 Ã— 210 pixel Image in higher resolution (1050 Ã— 276 pixel, file size: 8 KB, MIME type: image/png) PSU 90-125 Winglet airfoil designed by Dr. Mark D. Maughmer and Michael Selig at the Pennsylvania State University. ... Image File history File links Size of this preview: 800 Ã— 210 pixel Image in higher resolution (1050 Ã— 276 pixel, file size: 8 KB, MIME type: image/png) PSU 90-125 Winglet airfoil designed by Dr. Mark D. Maughmer and Michael Selig at the Pennsylvania State University. ... Rutan VariEze, the first aircraft to use winglets in 1975 Learjet 28/29, the first production jet aircraft to use winglets in 1977 McDonnell Douglas MD-11, the first mainline airliner to feature winglets in 1990 Wingtip devices are usually intended to improve the efficiency of fixed-wing aircraft. ...

Aerofoil terminology

The various terms related to airfoils are defined below:^[1]

The mean camber line is a line drawn half way between the upper and lower surfaces.
The chord line is a straight line connecting the leading and trailing edges of the airfoil, at the ends of the mean camber line.
The chord is the length of the chord line and is the characteristic dimension of the airfoil section
The maximum thickness and the location of maximum thickness are expressed as a percentage of the chord

An airfoil section is nicely displayed at the tip of this Denney Kitfox aircraft (G-FOXC), built in 1991.

Image File history File linksMetadata Download high resolution version (1800x1301, 759 KB) An aerofoil section is well displayed at the wing tip of this Denney Kitfox (G-FOXC), built in 1991. ... Image File history File linksMetadata Download high resolution version (1800x1301, 759 KB) An aerofoil section is well displayed at the wing tip of this Denney Kitfox (G-FOXC), built in 1991. ...

Thin Airfoil Theory

A simple mathematical theory of 2-D thin airfoils was devised by Ludwig Prandtl and others in the 1920s. Ludwig Prandtl (4 February 1875 - 15 August 1953) was a German physicist. ... The 1920s is a decade that is sometimes referred to as the Jazz Age or the Roaring Twenties, usually applied to America. ...

The airfoil is modeled as a thin lifting mean-line (camber line). The mean-line, y(x), is considered to produce a distribution of vorticity $γ(s)$ along the line, s. By the Kutta condition, the vorticity is zero at the trailing edge. Since the airfoil is thin, x (chord position) can be used instead of s, and all angles can be approximated as small. Vorticity is a mathematical concept used in fluid dynamics. ... The Kutta condition is a principle in fluid dynamics, especially aerodynamics, applied at sharp corners such as trailing edges of airfoils in steady flow. ...

From the Biot-Savart law, this vorticity produces a flow field $w (s)$ where The Biot-Savart law is a physical law with applications in both electromagnetics and fluid dynamics. ...

$w(x) = frac{1} {(2 pi)} int_{0}^{c} frac {gamma (x')}{(x-x')} dx'$

where x is the location at which induced velocity is produced, x' is the location of the vortex element producing the velocity and c is the chord length of the aerofoil.

Since there is no flow normal to the curved surface of the airfoil, w(x) balances that from the component of main flow V which is locally normal to the plate - the main flow is locally inclined to the plate by an angle $α - d y / d x$ . That is

$V . (alpha - dy/dx) = w(x) = frac{1} {(2 pi)} int_{0}^{c} frac {gamma (x')}{(x-x')} dx'$

This integral equation can by solved for $γ(x)$ , after replacing x by

$x = c(1 - cos (theta ))/2$ ,

as a Fourier series in $A n s i n (n θ)$ with a modified lead term $A 0 (1 + c o s (θ)) / s i n (θ)$

That is $frac{gamma(theta)} {(2V)} = A_0 frac {(1+cos(theta))} {sin(theta)} + sum A_n . sin (n theta))$

(These terms are known as the Glauert integral). Hermann Glauert, FRS (1892-1934) was a British aerodynamicist and Principal Scientific Officer of the Royal Aircraft Establishment, Farnborough until Dec 1934. ...

The coefficients are given by $A_0 = alpha - frac {1}{pi} int_{0}^{pi} ((dy/dx) . dtheta$

and $A_n = frac {2}{pi} int_{0}^{pi} cos (n theta) (dy/dx) . dtheta$

By the Kutta-Joukowski theorem, the total lift force F is proportional to The lift force, lifting force or simply lift is a mechanical force generated by a solid object moving through a fluid. ...

$rho V int_{0}^{c} gamma (x). dx$

and its moment M about the leading edge to $rho V int_{0}^{c} x.gamma (x) . dx$

The calculated Lift coefficient depends only on the first two terms of the Fourier series, as

$C_L = 2 pi (A_0 + A_1/2)$

The moment M about the leading edge depends only on $A 0, A 1 a n d A 2$ , as

$C_M = - 0.5 pi (A_0+A_1-A_2/2)$

The moment about the 1/4 chord point will thus be,

$C_M(1/4c) = - pi /4 (A_1 - A_2)$ .

From this it follows that the center of lift is aft of the 'quarter-chord' point 0.25 c, by The Center of lift (or CoP) is the point on a body where the sum of the total pressure acts. ...

$Delta x /c = pi /4 ((A_1-A_2)/C_L)$

The aerodynamic center is at the quarter-chord point. The AC is where the pitching moment M' does not vary with angle of attack ie The aerodynamic center of an airfoil moving through a fluid is the point at which the pitching moment generated by the airfoil is constant regardless of the angle of attack[1], [2]. This is an aspect of aerodynamics. ...

$frac { partial (C_{M'}) }{ partial (C_L)} = 0$

Reference (thin airfoil/aerofoil theory)

The following is typical of many references on this subject

[1] [2]

External links

References

^ Hurt, H. H., Jr. [1960] (January 1965). Aerodynamics for Naval Aviators. U.S. Government Printing Office, Washington D.C.: U.S. Navy, Aviation Training Division, pp. 21-22. NAVWEPS 00-80T-80.

Categories: Articles lacking sources from December 2006 | All articles lacking sources | Aerodynamics | Wing design

Results from FactBites:

The Airfoil Misconception in K-6 Textbooks (7271 words)
	Because of inertia, the trailing edge of a cambered airfoil itself behaves as a tilted plane, and therefore the airfoil effectively has a positive angle which causes air to be deflected.
	To create adequate lift at extremely low speeds, an airfoil must be operated at a large angle of attack, and this leads to airflow detachment from wing's the upper surface (stall.) To prevent this, the airfoil must be carefully shaped.
	Cambered airfoils create lift at zero AOA, which proves that the "Newtonian" theory of lift is wrong.

Laminar Flow Airfoil (1694 words)
	The theory in using an airfoil of this design was to maintain the adhesion of the boundary layers of airflow which are present in flight as far aft of the leading edge as possible.
	The use of this airfoil on the Mustang would greatly add to the drag reducing concept that was paramount in all design phases of the airplane.
	The usual definition of a laminar flow airfoil is that the favorable pressure gradient ends somewhere between 30 and 75% of chord.

More results at FactBites »

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