A method is described that estimates the error in the static pressuremeasurement on an aircraft from differential pressure measurements on thehemispherical surface of a Rosemount model 858AJ air velocity probe mountedon a boom ahead of the aircraft. The theoretical predictions for how thepressure should vary over the surface of the hemisphere, involving an unknownsensitivity parameter, leads to a set of equations that can be solved for theunknowns – angle of attack, angle of sideslip, dynamic pressure and theerror in static pressure – if the sensitivity factor can be determined. Thesensitivity factor was determined on the University of Wyoming King Airresearch aircraft by comparisons with the error measured with a carefullydesigned sonde towed on connecting tubing behind the aircraft – a trailingcone – and the result was shown to have a precision of about ±10 Pa over awide range of conditions, including various altitudes, power settings, andgear and flap extensions. Under accelerated flight conditions, geometricaltitude data from a combined Global Navigation Satellite System (GNSS) andinertial measurement unit (IMU) system are used to estimate accelerationeffects on the error, and the algorithm is shown to predict corrections to aprecision of better than ±20 Pa underthose conditions. Some limiting factors affecting the precision of staticpressure measurement on a research aircraft are discussed.
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