Section thickness is another parameter that has an influence on wing performance, but different aeronautical references give different views on its effect. For certain symmetrical wing profiles (such as the NACA 0006, 0009 and 0012, having zero camber, and thickness from 0.06c to 0.12c) the stall was said to become more ‘abrupt’ as thickness was increased, while for other non-symmetrical sections (eg the NACA 2412, 2415 and 2418, each having 2% maximum camber at 0.4c, with thickness from 0.12c to 0.18c), increased thickness seemed to lead to a more gentle stall, but a lower peak lift coefficient. When the thickness of these profiles was increased beyond 0.12c, the maximum-CL value actually tailed off slightly again, and the implication of this is that if a wing is intended to remain as a single-element devie, a maximum thickness of 0.12c could be construed as a design parameter. Howerer, very thin wing profiles seem to be associated with an abrupt stall, caused by ‘leading edge separation’, a phenomenon caused by too rapid acceleration of the airflow around the leading edge of the wing.