File:Airfoil thickness definition.svg

Summary

Two different and incompatible definitions of <a href="https://en.wikipedia.org/wiki/Airfoil" class="extiw" title="en:Airfoil">airfoil</a> 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"^{<a href="#cite_note-Houghton-1">[1]</a>} and can be seen in Houghton & Carpenter 2003,^{<a href="#cite_note-Houghton-1">[1]</a>} Phillips 2010.^{<a href="#cite_note-2">[2]</a>}

• 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^{<a href="#cite_note-3">[3]</a>}.

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 href="#cite_ref-Houghton_1-0">^a</a> <a href="#cite_ref-Houghton_1-1">^b</a> Houghton, E. L.; Carpenter, P.W. (2003) Butterworth Heinmann , ed. Aerodynamics for Engineering Students (5^th ed.) <a href="https://en.wikipedia.org/wiki/International_Standard_Book_Number" class="extiw" title="en:International Standard Book Number">ISBN</a>: <a href="//commons.wikimedia.org/wiki/Special:BookSources/0750651113" title="Special:BookSources/0750651113">0750651113</a>. p.17
2. <a href="#cite_ref-2">↑</a> Phillips, Warren F. (2010) Mechanics of Flight (2^nd ed.), Wiley & Sons <a href="https://en.wikipedia.org/wiki/International_Standard_Book_Number" class="extiw" title="en:International Standard Book Number">ISBN</a>: <a href="//commons.wikimedia.org/wiki/Special:BookSources/9780470539750" title="Special:BookSources/9780470539750">9780470539750</a>. p.27
3. <a href="#cite_ref-3">↑</a> Bertin, John J.; Cummings, Russel M. (2009) Pearson Prentice Hall , ed. Aerodynamics for Engineers (5^th ed.) <a href="https://en.wikipedia.org/wiki/International_Standard_Book_Number" class="extiw" title="en:International Standard Book Number">ISBN</a>: <a href="//commons.wikimedia.org/wiki/Special:BookSources/9780132272681" title="Special:BookSources/9780132272681">9780132272681</a>. p.199

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