Engineering methods applied to a UCAV configuration : some aerodynamic design considerations

To reduce development cost and to avoid late design fixes in aircraft design, methods that are fast and economic in estimating the aerodynamic characteristics of complex flight vehicles at the preliminary design stage are desired. This work and thesis focus on the adaptive-fidelity CFD approach, with emphasis on the high end of the CFD tools available today. The core idea of the method is to use computationally cheap modeling in the part of the flight envelope where it is applicable. When the complexity in the flow field increases more details and realism is included in the mathematical model, at a computationally higher cost. A typical case where this would be required could be at the border of the flight envelope, where flow phenomena such as shocks, flow separation, and interacting vortex systems could occur. Since the number of cases needed to resolve the flight envelope could be in the order of ten thousands automation is required. The bottlenecks are the discretization of the fluid volume and evaluation of raw CFD data and post processing of the data. These issues are also discussed in this work. The method has been tested on two real flying aircraft, the X-31 delta-winged aircraft with vector thrust, and the Ranger 2000 Jet trainer, as well as on the SACCON preliminary wing-body UCAV design. The results provide improved understanding of the usefulness of this method as an analysis tool during the preliminary design phase all the way into the flight test diagnostic phase of a new aircraft.