Generalised aerodynamic forces on a T-tail oscillating harmonically in subsonic flow

Abstract

The T-tail under investigation consists of a flat horizontal tailplane mounted on top of a flat vertical fin. The chords of the two surfaces at their junction are of the same length and are coincident. The T-tail is assumed to be isolated and to be oscillating harmonically in a subsonic flow whose main stream is parallel to the mean positions of the surfaces of the T-tail. The linearised equations of potential flow are assumed to be valid. A pair of integral equations relating the normal air velocities on the surfaces of the tailplane and fin with the loading distributions on these surfaces is derived. This pair of simultaneous equations is solved approximately by collocation and the loading functions so determined are used to calculate generalised airforces on the T-tail at any frequency of oscillation. When the T-tail is attached to an aircraft there is some aerodynamic interaction between the aircraft fuselage and the T-tail. It has not been possible to estimate this interaction in general. If the T-tail is attached to an infinite wall with the tailplane parallel to the wall then it is possible to obtain the interaction by the method of images with the infinite wall acting as a reflector. This approaches conditions in a wind tunnel, so a treatment of this case has been given. This case may also be a guide to the more general case of interaction between a fuselage and a T-tail. The procedures have been programmed for the Ferranti Mercury Computer.