In aeronautics, the chord is an imaginary straight line joining the leading edge and trailing edge of an aerofoil. The chord length is the distance between the trailing edge and the point where the chord intersects the leading edge.[1][2] The point on the leading edge used to define the chord may be the surface point of minimum radius.[2] For a turbine aerofoil the chord may be defined by the line between points where the front and rear of a 2-dimensional blade section would touch a flat surface when laid convex-side up.[3]
Airfoil nomenclature showing chord line
Chord line of a turbine airfoil section.
Chords on a swept-wing
The wing, horizontal stabilizer, vertical stabilizer and propeller/rotor blades of an aircraft are all based on aerofoil sections, and the term chord or chord length is also used to describe their width. The chord of a wing, stabilizer and propeller is determined by measuring the distance between leading and trailing edges in the direction of the airflow. (If a wing has a rectangular planform, rather than tapered or swept, then the chord is simply the width of the wing measured in the direction of airflow.) The term chord is also applied to the width of wing flaps, ailerons and rudder on an aircraft.
The term is also applied to compressor and turbine aerofoils in gas turbine engines such as turbojet, turboprop, or turbofan engines for aircraft propulsion.
Many wings are not rectangular, so they have different chords at different positions. Usually, the chord length is greatest where the wing joins the aircraft's fuselage (called the root chord) and decreases along the wing toward the wing's tip (the tip chord). Most jet aircraft use a taperedswept wing design. To provide a characteristic figure that can be compared among various wing shapes, the mean aerodynamic chord (abbreviated MAC) is used, although it is complex to calculate. The mean aerodynamic chord is used for calculating pitching moments.[4]
Standard mean chord (SMC) is defined as wing area divided by wing span:[5]
where S is the wing area and b is the span of the wing. Thus, the SMC is the chord of a rectangular wing with the same area and span as those of the given wing. This is a purely geometric figure and is rarely used in aerodynamics.
where y is the coordinate along the wing span and c is the chord at the coordinate y. Other terms are as for SMC.
The MAC is a two-dimensional representation of the whole wing. The pressure distribution over the entire wing can be reduced to a single lift force on and a moment around the aerodynamic center of the MAC. Therefore, not only the length but also the position of MAC is often important. In particular, the position of center of gravity (CG) of an aircraft is usually measured relative to the MAC, as the percentage of the distance from the leading edge of MAC to CG with respect to MAC itself.
Note that the figure to the right implies that the MAC occurs at a point where leading or trailing edge sweep changes. In general, this is not the case. Any shape other than a simple trapezoid requires evaluation of the above integral.
The ratio of the length (or span) of a rectangular-planform wing to its chord is known as the aspect ratio, an important indicator of the lift-induced drag the wing will create.[7] (For wings with planforms that are not rectangular, the aspect ratio is calculated as the square of the span divided by the wing planform area.) Wings with higher aspect ratios will have less induced drag than wings with lower aspect ratios. Induced drag is most significant at low airspeeds. This is why gliders have long slender wings.
^V., Cook, M. (2013). Flight dynamics principles : a linear systems approach to aircraft stability and control (3rd ed.). Waltham, MA: Butterworth-Heinemann. ISBN9780080982427. OCLC 818173505.
^Abbott, I.H., and Von Doenhoff, A.E. (1959), Theory of Wing Sections, Section 1.4 (page 27), Dover Publications Inc., New York, Standard Book Number 486-60586-8
^Kermode, A.C. (1972), Mechanics of Flight, Chapter 3, (p.103, eighth edition), Pitman Publishing Limited, London ISBN0-273-31623-0
^Ruggeri, M.C., (2009), Aerodinámica Teórica, Apuntes de la materia, UTN-FRH, Haedo, Buenos Aires
External links
Aerodynamics for Students
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May 16, 2023
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See also Wing chord biology In aeronautics the chord is an imaginary straight line joining the leading edge and trailing edge of an aerofoil The chord length is the distance between the trailing edge and the point where the chord intersects the leading edge 1 2 The point on the leading edge used to define the chord may be the surface point of minimum radius 2 For a turbine aerofoil the chord may be defined by the line between points where the front and rear of a 2 dimensional blade section would touch a flat surface when laid convex side up 3 Airfoil nomenclature showing chord line Chord line of a turbine airfoil section Chords on a swept wing The wing horizontal stabilizer vertical stabilizer and propeller rotor blades of an aircraft are all based on aerofoil sections and the term chord or chord length is also used to describe their width The chord of a wing stabilizer and propeller is determined by measuring the distance between leading and trailing edges in the direction of the airflow If a wing has a rectangular planform rather than tapered or swept then the chord is simply the width of the wing measured in the direction of airflow The term chord is also applied to the width of wing flaps ailerons and rudder on an aircraft The term is also applied to compressor and turbine aerofoils in gas turbine engines such as turbojet turboprop or turbofan engines for aircraft propulsion Many wings are not rectangular so they have different chords at different positions Usually the chord length is greatest where the wing joins the aircraft s fuselage called the root chord and decreases along the wing toward the wing s tip the tip chord Most jet aircraft use a tapered swept wing design To provide a characteristic figure that can be compared among various wing shapes the mean aerodynamic chord abbreviated MAC is used although it is complex to calculate The mean aerodynamic chord is used for calculating pitching moments 4 Contents 1 Standard mean chord 2 Mean aerodynamic chord 3 Tapered wing 4 References 5 External linksStandard mean chord EditStandard mean chord SMC is defined as wing area divided by wing span 5 SMC S b displaystyle mbox SMC frac S b where S is the wing area and b is the span of the wing Thus the SMC is the chord of a rectangular wing with the same area and span as those of the given wing This is a purely geometric figure and is rarely used in aerodynamics Mean aerodynamic chord EditMean aerodynamic chord MAC is defined as 6 MAC 2 S displaystyle mbox MAC frac 2 S 0 b 2 c y 2 d y displaystyle int 0 frac b 2 c y 2 dy where y is the coordinate along the wing span and c is the chord at the coordinate y Other terms are as for SMC The MAC is a two dimensional representation of the whole wing The pressure distribution over the entire wing can be reduced to a single lift force on and a moment around the aerodynamic center of the MAC Therefore not only the length but also the position of MAC is often important In particular the position of center of gravity CG of an aircraft is usually measured relative to the MAC as the percentage of the distance from the leading edge of MAC to CG with respect to MAC itself Note that the figure to the right implies that the MAC occurs at a point where leading or trailing edge sweep changes In general this is not the case Any shape other than a simple trapezoid requires evaluation of the above integral The ratio of the length or span of a rectangular planform wing to its chord is known as the aspect ratio an important indicator of the lift induced drag the wing will create 7 For wings with planforms that are not rectangular the aspect ratio is calculated as the square of the span divided by the wing planform area Wings with higher aspect ratios will have less induced drag than wings with lower aspect ratios Induced drag is most significant at low airspeeds This is why gliders have long slender wings Tapered wing Edit Taper ratio redirects here For taper ratio in space elevator construction see Space elevator Cable materials Knowing the area Sw taper ratio l displaystyle lambda and the span b of the wing the chord at any position on the span can be calculated by the formula 8 c y 2 S w 1 l b 1 1 l b 2 y displaystyle c y frac 2 S w 1 lambda b left 1 frac 1 lambda b 2y right wherel C T i p C R o o t displaystyle lambda frac C rm Tip C rm Root References Edit L J Clancy 1975 Aerodynamics Section 5 2 Pitman Publishing Limited London ISBN 0 273 01120 0 a b Houghton E L Carpenter P W 2003 Butterworth Heinmann ed Aerodynamics for Engineering Students 5th ed ISBN 0 7506 5111 3 p 18 https www abbottaerospace com downloads nasa sp 290 turbine design and application p 66 dead link The Design Of The Aeroplane Darrol Stinton 1984 ISBN 0 632 01877 1 p 26 V Cook M 2013 Flight dynamics principles a linear systems approach to aircraft stability and control 3rd ed Waltham MA Butterworth Heinemann ISBN 9780080982427 OCLC 818173505 Abbott I H and Von Doenhoff A E 1959 Theory of Wing Sections Section 1 4 page 27 Dover Publications Inc New York Standard Book Number 486 60586 8 Kermode A C 1972 Mechanics of Flight Chapter 3 p 103 eighth edition Pitman Publishing Limited London ISBN 0 273 31623 0 Ruggeri M C 2009 Aerodinamica Teorica Apuntes de la materia UTN FRH Haedo Buenos AiresExternal links EditAerodynamics for Students wayback machine 1 Finding the Mean Aerodynamic Chord MAC Image based Mean Aerodynamic Chord MAC calculator Retrieved from https en wikipedia org w index php title Chord aeronautics amp oldid 1072819283, wikipedia, wiki, book, books, library,
