English: Two different and incompatible definitions of airfoil thickness are used in the aerodynamics field (here illustrated on the same airfoil).

• In case A above the thickness is measured perpendicular to the foil camber line. This is sometimes described as the "American convention"^[1] and can be seen in Houghton & Carpenter 2003,^[1] Phillips 2010.^[2]

• In case B above the thickness is measured perpendicular to the foil chord line. This is sometimes described as the "British convention" and can be seen in Bertin & Cummings 2009^[3].

Note that each definition implies a different camber line geometry for a given airfoil. Since the camber line curvature is small on most aircraft, the effect of difference between the definitions is often small.

1. ↑ ^{a b} Houghton, E. L.; Carpenter, P.W. (2003年) Butterworth Heinmann , ed. 《 Aerodynamics for Engineering Students》 (第5 ed.) ISBN： 0750651113. p.17
2. ↑ Phillips, Warren F. (2010年) 《 Mechanics of Flight》 (第2 ed.)、​Wiley & Sons ISBN： 9780470539750. p.27
3. ↑ Bertin, John J.; Cummings, Russel M. (2009年) Pearson Prentice Hall , ed. 《 Aerodynamics for Engineers》 (第5 ed.) ISBN： 9780132272681. p.199