PERFORMANCE CHARACTERISTICS OF FLUSH ANGLE-OF-ATTACK MEASUREMENT SYSTEM INTEGRATED ON A PITOT TUBE

In this paper the performance characteristics of a pressure based flush angle-of-attack measurement system, integrated on a Pitot-Static tube, is presented. The non-dimensional pressure difference between two static pressure ports located on the upper and lower surface of the conical interface, with half-cone-angle of 20 degrees, of the Pitot tube shows linear behavior (desirable) with angle-of-attack in the subsonic regime while in the supersonic regime it has non-linear behavior (undesirable). This non-linear behavior is attributed to shockwave induced flow separation just upstream of the conical interface. The undesirable non-linear trend can be eliminated by reducing the half-cone-angle of the conical interface from 20 to 12 degrees. The reduction in half-cone-angle eliminates the upstream shockwave induced flow separation in the supersonic regime thereby restoring the linear behavior between non-dimensional pressure difference and angle-of-attack. However, reducing the conical interface half-cone-angle also reduces the sensitivity of the angle-of-attack measurement system in the subsonic regime by 18%. Computational Fluid Dynamics tools have been used in the analysis and refinement of flush angle-of-attack measurement system. The complete Mach number regime (Mach<2) has been computationally analyzed for the two conical interfaces. The results presented in this study have been validated by subsequent wind tunnel tests.