Wind Measurements on a Maneuvering Twin-Engine Turboprop Aircraft Accounting for Flow Distortion

Traditional techniques for the calibration of the aircraft-relative wind vector from flight maneuvers are discussed with special regard to the effects of perturbations in the flow patterns around the aircraft body during periods of significant accelerations and angular rates (rapidly varying motion). A procedure is developed that allows both unbiased determination of steady-flight calibration parameters and explicit determination and characterization of errors in measured flow quantities that result from flow perturbations induced during the rapidly varying motion. This technique is applied to the case of air vector measurements from a five-hole pressure probe mounted under the wing of a Convair 580 research aircraft operated by the Canadian National Research Council. Results indicate that during pitching, yawing, and rolling maneuvers air data measurements at the pressure probe contain substantial errors that are associated with adjustments of the oncoming airflow to the sudden wing translations and rotations, as well as associated with variations in the strength and pattern of the along-wing sidewash circulation. In addition, the fuselage-measured static pressure position error is strongly affected by pressure pattern changes during strong longitudinal accelerations and, to a lesser extent, by lateral and normal accelerations during pitching and yawing motions. Empirical corrections to the pressure probe and static pressure measurements are derived to account for these effects, using multiple regression techniques. Under steady flight conditions, these corrections are small, but during rapid maneuvers they reduce the peak-to-trough errors in the derived earth-relative winds from ±1.5 m s−1 (uncorrected) to around ±0.6 m s−1 in the case of the horizontal wind components, and ±0.4 m s−1 in the case of vertical wind components.