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An experimental study on aerodynamic coefficients of a lambda wing configuration was performed at the low speed wind tunnel of Agency for Defense Development. The main purpose of this study was to investigate the effects of sideslip angle on various aerodynamic coefficients. In the case of 0° sideslip angle, nose-up pitching moment rapidly increases at a specific angle of attack. This unstable pitching moment characteristic is referred to as pitch break or pitch up. As the sideslip angle increases, the pitch break is found to be generated at a higher angle of attack. Rolling moment is found to show similar behavior pattern to 'pitch break' style with angle of attack at non-zero sideslip angles. This trend gets severer at greater sideslip angles. Yawing moment also shows substantial variation of the slope and the unstable directional stability with sideslip angles at higher angles of attack. These characteristics of the three moments clearly implies the difficulty of the flight control which requires efficient control augmentation system.

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This paper presents a new approach in resolving discontinuities between subspaces when the subspace partitioning method is applied to measure aerodynamic coefficients. The discontinuities between response surfaces in each subspace are hard to resolve in an analytical method, but it can be smoothened by overlapping between subspaces and integrating with proper interpolation. The traditional One Factor at a Time (OF AT) method is used for gathering aerodynamic force and moment coefficient data before applying the Design of Experiments (DOE) method for the purpose of later validation of the suggested method. In each subspace, the Central Composite Design (CCD) is used to reduce experimental points. The Separated Response Surface Model compared to the Integrated Response Surface Model. Quality of fit of the Developed Integrated Model calculated with OF A T data for validation. The test model base is the lambda wing configuration of the UCAV 1303. The study was carried out at the low speed wind tunnel of the Agency for Defense Development (ADD-LSWT).

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