barit and Jane,
Originally Posted by PBL
It wasn't so obvious to me what ["crest"] meant, because I could think of two plausible meanings. One was point of maximum thickness; the other was point of maximum upwards deviation from chord.
Of course my suggestions are also ambiguous, because of where the "point" might be located - on the surface, or on the chord (which is normally taken to be the axis of coordinates).
I asked by aerodynamics guru, who said he understood it as meaning the highest point on the upper surface of the wing, and pointed me to Shevell, (his edition p193; my, first, edition, p188, first page of Chapter 12), where it is defined as the "point on the airfoil upper surface to which the freestream is tangent".
So, yes, it seems to be a common term, but it means the second of my proposed definitions, not the first!
PBL