Directional Stability Issues of a Three Lifting Surface Aircraft

This paper deals with the evaluation of the interference effects among aircraft components in a three lifting surface configuration, an innovative layout for a high-capacity turboprop (130 pax), which is supposed to be competitive with respect to short/medium haul regional jets. The feasibility study of such a configuration is framed within the Innovative turbopROp configuratioN (IRON) project. An experimental wind tunnel test campaign has been performed on a 1:25 scaled model at the main subsonic wind tunnel facility of the Industrial Engineering Department of the University of Naples Federico II. Beside the well-known detrimental effects of the angle of attacK on the sidewash, the experimental tests have highlighted a strong directional stability reduction due to the canard interference with both the fuselage and the vertical tail. Results have shown that the canard increases the fuselage instability of about 14%. The canard wake displacement also affects the aircraft directional stability. Results collected in this work have been useful to perform a redesign of the aircraft empennage and to schedule numerical high-fidelity analyses as well as a second wind tunnel test campaign on the updated aircraft model to get further insights on the aerodynamic interference, including propulsive effects.