The use of theodolite intersections to calibrate a wind tunnel probe

The 30x60 feet wind tunnel at the NASA Langley Research Center is a major facility capable of testing full size aircraft. Air pressure measurements recorded during aerodynamic tests of aircraft or models are made using a probe attached to a three axis carriage. Positioning of the carriage during tests is made using manual observations of survey tapes and an electronic counter. Observations with three theodolites were used to calibrate the location of the carriage relative to an orthogonal coordinate system with a vertical axis. Calibrations were carried out with both the air flow off and the air flow on to assess the influence of induced vibrations on the measurements and the displacement of the carriage under wind load. A variety of coordinate transformations were used to analyse the data, demonstrate the subjectivity of the manual observations and provide a mathematical correction for the observed data.