Development of a Flush Airdata Sensing System on a Sharp-Nosed Vehicle for Flight at Mach 3 to 8

NASA Dryden Flight Research Center has developed a flush airdata sensing (FADS) system on a sharp-nosed, wedge-shaped vehicle. This paper details the design and calibration of a real-time angle-ofattack estimation scheme developed to meet the onboard airdata measurement requirements for a research vehicle equipped with a supersonic-combustion ramjet engine. The FADS system has been designed to perform in flights at speeds between Mach 3 and Mach 8 and at angles of attack between –6° and 12°. The description of the FADS architecture includes port layout, pneumatic design, and hardware integration. Predictive models of static and dynamic performance are compared with wind-tunnel results across the Mach and angle-of-attack range. Results indicate that static angle-of-attack accuracy and pneumatic lag can be adequately characterized and incorporated into a real-time algorithm. NOMENCLATURE Acronyms FADS flush airdata sensing INS inertial navigation system L pneumatic line designation PPT precision pressure transducer SCRamjet supersonic-combustion ramjet Symbols transducer calibration as a function of Mach number D diameter of lines from port to transducer, in. forward angle-of-attack estimate, deg rear angle-of-attack estimate, deg pseudodifferential angle-of-attack estimate, deg g acceleration caused by gravity, ft/sec2 i arbitrary integer k lag constant L pneumatic line length, ft PPPT measured pressure at transducer, lbf/ft 2 Pport measured pressure at port, lbf/ft 2 dynamic pressure, lbf/ft2 q1 weighting function s Laplace frequency variable CPPT α1 α2 α3