Lift due to interference between an aerofoil and an external non-lifting body

Abstract

This paper contains an attempt to explain the incremental negative or positive lift induced on an aerofoil by an external non-lifting body (such as an engine nacelle), as observed in some experiments. A two-dimensional theory is proposed, based on representing the body by a system of sources and sinks, and by determining their effect on the aerofoil by means of a suitable conformal transformation. Two simple cases are considered: a semi-infinite body corresponding to a single source, and a finite body of oval shape corresponding to one source and one sink. Formulae for the induced-lift coefficient and for the position of centre of pressure are derived and illustrated by diagrams. Only incompressible flow is considered.