A method is described of calibrating airspeed installations on airplanes at transonic and supersonic speeds by use of instrumentation in the airplane only. The method consists in first making a survey of temperature, static pressure, and total pressure over the desired range of altitudes at speeds for which the airspeed calibration is known. The airplane is then flown at speeds for which the calibration is desired through the range of altitude surveyed, and the measurements of temperature, static pressure, and total pressure are repeated. The values of total pressure and indicated temperature at a given instant in the calibration run, together with the temperature recovery factor of the thermometer, define the relation between ambient temperature and static pressure' at that instant. Comparison of this relation with that determined from the survey gives the value of free-stream static pressure at that instant. The static-pressure error is then obtained by subtracting the free-stream static pressure from the indicated static pressure. This method requires precise measurements of temperature. An accuracy in the calibration of 1.0 percent of Mach number near a Mach number of 1.0 corresponds to an accuracy in the measurement of temperature of1/2 F below and 2° F above the tropopause.
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