HART II Blade Motion Measured by Stereo Pattern Recognition (SPR)

The wind tunnel test of HART II (Higher Harmonic Control Aeroacoustic Rotor Test), performed in October 2001 in the Large Low-Speed Facility (LLF) of the German-Dutch Wind-tunnel (DNW), is part of an international cooperative program by the German DLR, French ONERA, DNW, NASA Langley and the US Army Aeroflightdynamics Directorate (AFDD). The main objective of the program is the investigation of rotor wake and its influence on rotor blade-vortex interaction (BVI) noise with and without higher harmonic pitch control (HHC). For blade position and deflection measurements the Stereo Pattern Recognition (SPR) technique was used for the first time. This technique is based on a 3-dimensional reconstruction of visible marker locations by using stereo camera images. An evaluation of these images leads to the spatial position of markers which are attached to each of the four blades and to the bottom of the fuselage and thus to the blade motion parameters in flap, lead-lag and torsion. In this paper the different analysis methods and post-processing of SPR data are presented and the advantages, drawbacks and the potential of this technology are shown.