Estimates of the lift reduction due to boundary layer on two-dimensional aerofoils

Abstract

Experimental values of the reduction in lift curve slope due to boundary layer on two-dimensional aerofoils in incompressible flow are compared with estimates derived from the Royal Aeronautical Society Data Sheet and estimates calculated by Spence's theoretical method. The Data Sheet is shown to under-estimate the lift slope in some cases where transition is not fixed at the leading edge and it is suggested that this is due to the effect upon lift of the movement of transition position with incidence. It is proposed that the Data.Sheet should be modified to indicate the limiting values between which the slope of the lift curve should lie. No more accurate method of assessing the effect of transition movement seems possible but it is thought that the uncertainty will be small in full scale practical cases.