Aerodynamic Design Guidelines of Aircraft Dorsal Fin

The present paper aims to provide aerodynamic design guidelines for an aircraft dorsal fin, obtained using CFD RANS technique. A parametric aerodynamic investigation about dorsal fin length, height, sweep angle, and planform area has been performed in order to evaluate the effects of geometric variations on the dorsal fin and vertical tail aerodynamic behavior in sideslip conditions. More than 30 dorsal fin geometries have been investigated, mounted on a typical large turbopropeller fuselage with a vertical tail. Main results show that there is no effect of the dorsal fin up to 20° of sideslip angle. At higher angles, the vertical tail stalls and the flow field around the empennage is strongly influenced by two vortices generated by the dorsal fin intersection with the fuselage (primary vortex) and with the vertical tail (secondary vortex). The stall phenomenon appears around 35° of sideslip angle. Moreover, dorsal fin slightly reduced fuselage instability. Finally, some wind tunnel tests have been performed on two dorsal fin geometries to validate the numerical analyses. Experimental tests have shown a good agreement with CFD simulations and have given useful qualitative indications on the aerodynamic behavior of the vertical tail at high angles of sideslip, with and without dorsal fin.