On the use of wing adaptation and formation flight for improved aerodynamic efficiency

In the continuous effort to improve the performance and efficiency of today's aircraft, two different and innovative approaches for aircraft drag reduction are examined. These approaches are: (1) multiple spanwise trailing-edge flaps, and (2) formation and ground-effect flight. The main goal of this dissertation was to assess the drag benefits of the two approaches, in an effort to explore their potential for use on future aircraft.; By using multiple trailing-edge flaps along the wing span, it is possible to redistribute the spanwise lift distribution to suit the flight condition. A numerical approach was developed for determining optimum lift distributions on a wing with multiple trailing-edge flaps for various flight conditions. The primary objective was to determine the flap angles that, will reduce the drag at 1-g flight conditions, and constrain the wing root-bending moment at high-g conditions to not exceed a specified value. The results for the flap-angle distributions are presented for a planar and a nonplanar wing, along with post-design analysis and aircraft performance simulations used to validate the optimum flap-angle distributions determined using the numerical approach.; When examining formation and ground-effect flight, an optimum-downwash approach using a vortex-lattice implementation was used to study formations of wings loaded optimally for minimum induced drag with roll trim. An exact approach was also developed to examine the drag of elliptically-loaded wings in formation. The results show that elliptically-loaded wing formations have nearly the same drag as optimally-loaded wing formations. For a formation of planar wings, in or out of ground effect, the optimum lateral separation corresponds to a 9%-span overlap of wing tips. Large formations experience small additional benefits due to ground effect even at relatively large ground clearances of four wing spans. The shape of vee-formations, for equipartition of drag benefits, is found to be nearly independent of flight in or out of ground effect.; Overall, both approaches for aircraft drag reduction show potential for significant drag savings. It is believed that the presented research will further increase interest in such flight techniques; and thus advance their progression toward becoming viable solutions for drag reduction on future aircraft.