The Research on the Drag Reduction of Transport Aircraft Using Ventral Fins

The aerodynamic characteristics of the upswept tail of a transport aircraft are studied and the optimum arrangements of ventral fins to reduce the drag are evaluated. Two symmetric vortices emerge under the fuselage afterbody, which are the major causal factor of the additional pressure drag. A pair of fins installed under the fuselage, extruding the core of the vortices effectively damp the vortex. Parametric study shows that the length, height, location and yaw angle of the fins are the sensitive factors of drag reduction. Drag reduction of 0.0021 is achieved in wind tunnel test for typical cruise angle of attack (AoA). The pitching moment has nose down tendency and the longitudinal stability is reduced. The reason is that the pressure recovery of the bottom surface of the tail is improved by adding the fins, which is dependent on the AoA.