Dynamic Stall Flight Data, Effects of Pitch Rate, Surface Roughness and Ground Effect

Abstract

Internally-funded NRC dynamic stalling flight research has been conducted, using the NRC CT-133 research jet. Initial data analysis and results are presented for the parameter matrix of varying surface roughness, stall-entry pitch rates and the presence of ground effect. For the first set of such flight manoeuvres, inertial data, air data and video data of surface flow visualization, using low-density wing tufts, were recorded. The inertial and air data were used for the derivation of incidence angle, α, and integrated force coefficients, notably CL . The video records have been used to define the spanwise / chordwise position and nature of the onset of wing upper surface flow separation lines. Stall onset has been defined as the onset of a pitching moment break, as observed in the occurrence of an uncommanded pitch rate change. Considering surface roughness in the form of the application of sandpaper to the upper and lower wing surfaces, extending +8% c from the leading edge, the data for the unroughened wing showed that stall onset angle, αSO, increased with stall-entry pitch rate, qSE. However, for the roughened wing, αSO and αCLmzx generally reduced with increasing qSE, such that the combined effect of roughness and pitch rate resulted in reductions in αSO which were in exceedance of the Brumby curve prediction by up to 130% at intermediate roughness (#120 and-#80 grit). Ground effect (GE) on the #40 grit roughened wing, at low qSE, resulted in a further decrement in αSO of approximately 2°.