Design Space Exploration of Supersonic Formation Flying Focusing on Drag Minimization

This study investigates the drag characteristics of a supersonic formation-flying concept that aims to reduce wave drag and sonic boom via shock-wave and expansion-fan interaction. Because of the complex interaction patterns seen in three-aircraft formations, optimization was applied as a rational means for design. To consider both the cruise efficiency and the safety of the aircraft, the objective functions are chosen to be the total LID of the formation and the minimum separation distance among the aircraft. The design variables define the relative positions of the aircraft and, as for the coordinate definition, the skewed cylindrical coordinate system that has been proven to be very effective in extracting the physics of the flowfield was chosen. Optimization results show a good correlation with results from previous studies. However, optimization arrived at a formation that unexpectedly achieved high performances in regions of the design space in which the previous study suggested bad performance. These solutions took advantage of the design space of three-aircraft formations (i.e., the synergistic effects of the flowfield of the two leading aircraft) and exploited the difference between the design space of two-aircraft formations.