超音速飛行における機外とう載品の抵抗

Abstract

Drag of external stores installed on a supersonic aircraft deteriorates the performance like maximum speed, acceleration, endurance. Droptanks, pods, wing pylons belong to such stores. The drag coefficients of these stores are essential to estimate the performances, however, comparably difficult to acquire in supersonic region. When supersonic wind tunnel is not available, the coefficients can be derived through flight tests.The proposed method depends on a comparison of supersonic acceleration flights between the clean and the externally installed configurations. The test aircraft is flown successively in that different configurations.For each acceleration, flying altitude, starting speed of 0.9 Mach and initial aircraft weight are kept equal. Also the maximum engine power setting of after-burner is kept same all through the accelerations. Each acceleration range from 0.9 to 2.0 Mach is divided commonly into a number of small speed class. At each class, flight Mach number, time and fuel quantity representing aircraft weight or mass are recorded by the pilot.For each class, based on equation of motion of the aircraft, the drag of the stores is calculated from the difference of the products between the two configurations, the product being the aircraft mass multiplied by the acceleration rate. Then the drag coefficient is derived as usual and plotted for the supersonic range.As an example, drag coefficient for a wing pylon was derived from flight tests as 0.04 to 0.02 for the supersonic range regarding to its side area, and compared with the coefficient from wave and friction drag theory. Due to unfavorable flight conditions and lack of experience, the dispersions of the derived coefficients from the theory were not small.By improving measuring technique and choosing flight condition carefully, this method may bring more accurate drag data and may be suitable when the flight test is feasible with other missions.