Development of a Pneumatic High-Angle-of-Attack Flush Airdata Sensing System

Abstract

<div class="htmlview paragraph">A nonintrusive high-angle-of-attack flush airdata sensing system was installed and flight tested on the F-18 High Alpha Research Vehicle at the NASA Dryden Flight Research Facility. This system consists of a matrix of 25 pressure orifices arranged in concentric circles on the nose of the vehicle to determine angles of attack and sideslip, Mach number, and pressure altitude. During the course of the flight tests, it was determined that satisfactory results could be achieved using a subset of just nine ports.</div> <div class="htmlview paragraph">The high-angle-of-attack flush airdata sensing system was calibrated and demonstrated using reference airdata generated by way of minimum variance estimation techniques which blended airdata measurements from two wingtip airdata booms with inertial velocities, aircraft angular rates and attitudes, precision radar tracking, and meteorological analyses. Calibration results are presented.</div> <div class="htmlview paragraph">Although analyses were not performed on-board in real-time, the High Alpha Research Vehicle high-angle-of-attack flush airdata sensing system and resulting airdata algorithms were validated as being real-time capable using flight data in ground based simulations. Algorithm implementation, failure detection modes using a <i>x</i><sup>2</sup> “goodness-of-fit” test, and fault tolerance techniques using weighted least squares are described.</div> <div class="htmlview paragraph">Flight-test results are presented. Under moderate maneuvering conditions the high-angle-of-attack flush airdata sensing system was shown to give excellent results. Empirical verification was performed over a large portion of the High Alpha Research Vehicle flight envelope with a Mach number range from 0.15 to 1.20 and an angle-of-attack range from -8.0 to 55.0°. Angle-of-sideslip excursions covered the range from -15.0 to 15.0°.</div>