Research on analytical scaling method and scale effects for subscale flight test of blended wing body civil aircraft

Although a subscale flight test (SFT) is an essential step in the practical application of a blended wing body (BWB) civil aircraft, research on similarity scaling methods and the scale effects during a BWB SFT is still lacking. Therefore, this paper presents an analytical scaling method based on the standard atmospheric model and full-scale flight envelope for analysing the scale factor and flight altitude during the SFT of a BWB aircraft that uses the NPU-300 concept under different similarity conditions. The relations between the size of the subscale test vehicle (STV) and the similarity conditions are summarised, and the corresponding test scope is given. The results showed that under the premise of Froude number similarity, the minimum STV sizes were 51.54% and 75.19% of the full-scale aircraft to simulate Reynolds and Mach numbers, respectively. Extending the test altitude helped to relax the size requirements and broaden the test scope. Furthermore, a quantitative computational fluid dynamics (CFD) study of the scale effects and an analysis of the STV mass requirements were conducted for both high-speed and low-speed BWB SFTs. For the high-speed case, the scale effects mainly influenced the viscosity, surface velocity, and shock wave characteristics. The wing loading was the core parameter for the high-speed STV mass design. A 30% scaled STV with constant wing loading could control the lift–drag ratio loss to within 2.0. For the low-speed case, the scale effects changed the aerodynamic performance by reducing the boundary layer anti-separation ability and control surface efficiency. These coupling effects showed that the scale factor should be at least 50% to obtain the full-scale stall characteristics. The research on the analytical scaling method and scale effects reported in this paper can provide an approach and basis for BWB SFT design and data correction.