Analysis of a Radome Air-Motion System on a Twin-Jet Aircraft for Boundary-Layer Research

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  • 1 Department of Meteorology, Uppsala University, Uppsala, Sweden
  • 2 Department of Mechanical Engineering, University of California, Irvine. California
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Abstract

A “radome gust probe” system was installed on a twin-jet aircraft for the purpose of boundary-layer research. This system provided a useful relatively low-cost method for air motion and turbulence measurements on an aircraft already equipped with an inertial navigation system (INS) and a data acquisition system. An error analysis was made for the wind measurements and gave the limitations for the present system with an unmodified airliner-type INS, The major factors that limit the precision of the horizontal wind are the resolutions and accuracy of the aircraft ground speed components and the true heading. A simple method was devised to improve the heading resolution. From in-flight maneuvers, it was determined that the mean horizontal airspeed vector was accurate to <0.5 m s−1—limited by the long-term drift and oscillation errors from the INS-and that pitch and yaw contamination of the wind was less than 5%. The in-flight data indicate that there probably are unknown time lags within the INS, which degrade the wind vector measurement for anything but straight and level flight. Some intercomparisons were obtained from fly-by(s) past an instrumented 140-m tower. These showed general agreement between mean, variance and high-frequency spectral measurements of the velocity components and temperature. Flux or covariance comparisons were not as good, probably due both to the short flight tracks and a complex boundary layer structure at the tower.

Abstract

A “radome gust probe” system was installed on a twin-jet aircraft for the purpose of boundary-layer research. This system provided a useful relatively low-cost method for air motion and turbulence measurements on an aircraft already equipped with an inertial navigation system (INS) and a data acquisition system. An error analysis was made for the wind measurements and gave the limitations for the present system with an unmodified airliner-type INS, The major factors that limit the precision of the horizontal wind are the resolutions and accuracy of the aircraft ground speed components and the true heading. A simple method was devised to improve the heading resolution. From in-flight maneuvers, it was determined that the mean horizontal airspeed vector was accurate to <0.5 m s−1—limited by the long-term drift and oscillation errors from the INS-and that pitch and yaw contamination of the wind was less than 5%. The in-flight data indicate that there probably are unknown time lags within the INS, which degrade the wind vector measurement for anything but straight and level flight. Some intercomparisons were obtained from fly-by(s) past an instrumented 140-m tower. These showed general agreement between mean, variance and high-frequency spectral measurements of the velocity components and temperature. Flux or covariance comparisons were not as good, probably due both to the short flight tracks and a complex boundary layer structure at the tower.

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