Calibration of a Radome-Differential GPS System on a Twin Otter Research Aircraft for Turbulence Measurements
Abstract
A five-hole radome pressure probe at the nose of a small two-engine newly instrumented research aircraft
was combined with global positioning system (GPS) receivers in differential mode to obtain high frequency
measurements of the wind vector in the atmospheric boundary layer with possible accuracy (root-mean-square
error) of about 0.1 m s21. This low cost and simple system can provide wind velocity measurements of sufficient
accuracy to estimate turbulent fluctuations. Special aircraft maneuvers above the atmospheric boundary layer
were used to calibrate the radome probe. The analysis of these data showed that the static pressure defect has
a significant dependence on flow angles and is affected by the propellers when significant thrust is applied.
Using a simple method, the authors found that the pressure distribution on the radome deviated from the one
expected for airflow incident on a sphere by more than 5%, the authors also detected a problem in the attack
angle differential pressure sensor. The calibration of the local attack and sideslip flow angles due to flow distortion
by the aircraft was obtained using two different methods. The first method was a least wind variance one
assuming a linear form for the calibration of flow angles. This method is easy to use and can be applied in the
presence of turbulence, but does not reveal any possible nonlinear dependence or problems in the data. The
second method was a direct one that assumes near–zero mean vertical wind velocity above the boundary layer,
while an average horizontal wind was estimated using the airstream speed with respect to the aircraft and the
aircraft velocity from the differential GPS data. These methods gave similar results and, thus, increased the
reliability of the calibration. The performance of the calibration procedure of the whole system was tested by
examining the sensitivity of estimated wind components to the aircraft motion (about 5%) and the quality of
mean profiles and turbulence statistics in the boundary layer.
Description
The article of record as published may be found at http://dx.doi.org/10.1175/1520-0426(2002)019<0159:COARDG>2.0.CO;2
Rights
This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.Collections
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