Chord (aeronautics)

In aeronautics, chord refers to the imaginary straight line joining the leading and trailing edges of an aerofoil. The chord length is the distance between the trailing edge and the point on the leading edge where the chord intersects the leading edge.

The point on the leading edge that is used to define the chord can be defined as either the surface point of minimum radius, or the surface point that will yield maximum chord length.

The wing, horizontal stabilizer, vertical stabilizer and propeller 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 aerofoils in gas turbine engines such as turbojet, turboprop, or turbofan engines for aircraft propulsion.

Most wings are not rectangular so they have a different chord at different positions along their span. To give a characteristic figure that can be compared among various wing shapes, the mean aerodynamic chord, or MAC, is used. The MAC is somewhat more complex to calculate, because most wings vary in chord over the span, growing narrower towards the outer tips. This means that more lift is generated on the wider inner portions, and the MAC moves the point to measure the chord to take this into account.

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