An improved preliminary design methodology for aircraft directional stability prediction and vertical tailplane sizing

This work deals with the development of a new preliminary design method for aircraft directional stability and vertical tail sizing. It is focused on regional turboprop aircraft because of their economic advantage over regional jets on short routes, for the increasing oil price, and because of the market needs of new airplanes in the next 20 years. The focus on aircraft directional stability is due to the significant discrepancies that classical semi-empirical methods, as USAF DATCOM and ESDU, provide for some configurations, because they are based on NACA wind tunnel tests about models not representative of an actual transport airplane. This work exploits the CFD to calculate the aerodynamic interference among aircraft parts for hundreds configurations of a given layout, providing a useful method in aircraft preliminary design. A wind tunnel investigation involving about 180 configurations has validated the numerical approach. The innovation of the work concerns the numerical and experimental parametric study on the static directional stability of a model representative of the regional turboprop aircraft category and the direct measurement of the vertical stabilizer aerodynamic forces in the wind tunnel, in addition to the force and moments acting on the whole model. In this way, useful data about aerodynamic interference have been extracted from experimental tests, which are in good agreement with the results of numerical simulations.