Slender-body theory is used to calculate the lift and drag forces acting on a thin slender delta wing cambered to form part of the surface of a circular cone, in the type of flow in which separation is from the trailing edge only. The boundary condition satisfied by the flow on the wing surface is applied there, instead of on a nearby plane as is usual in linearized theory. This has relatively little effect on the overall forces on a wing at a given incidence. However, a large discrepancy arises between the overall forces at the incidence for which the singularity in the pressure at the leading edge vanishes, as calculated by the present and by the usual linearized theory. This is particularly important, since it is at this incidence that the type of flow treated is expected to be realized in a physical fluid. The lift-dependent drag factor found is below the usual linearized-theory value for this type of wing at the incidence of no leading-edge singularity; and, for large lift, is below unity, which is the minimum for a trailing vortex sheet which is effectively flat
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