An Improved Procedure for Prediction of Drag Polars of a Joined Wing Concept Using Physics-Based Response Surface Methodology

Creation and utilization of accurate drag polars is essential in the aircraft sizing and synthesis process. Existing sizing and synthesis codes are based on historical data and cannot capture the aerodynamics of a non-conventional aircraft at the conceptual design phase. The fidelity of the aerodynamic analysis should be enhanced to increase the designer's confidence in the results. Hence, there is need for a physics-based approach to generate the drag polars of an aircraft lying outside the conventional realm. The deficiencies of the legacy codes should be removed and replaced with higher fidelity meta-model representations. This is facilitated with response surface methodology (RSM), which is a mathematical and statistical technique that is suited for the modeling and analysis of problems in which the responses, the drag coefficients in this case, are influenced by several variables. The geometric input variables are chosen so that they represent a multitude of configurations. Analytically created Response Surface Equations then replace the empirical aerodynamic relations and historical data found in sizing and synthesis codes, such as Flight Optimization System (FLOPS). The response surface equations obtained can be used in the system level studies and optimization. The approach described here is a statistics based methodology, which combines the use of Design of Experiments and Response Surface Method. Computational aerodynamic codes based on linearized potential flow (HASC) and boundary layer theory (BDAP) are employed to generate the needed parametric relationships. The aforementioned process is demonstrated through the implementation on a joined-wing concept.