Experimental Investigation of Model Deformation on a High Aspect Ratio Aircraft at Transonic Speeds in ETW

In wind tunnel testing, especially under high aerodynamic loads, model deformation is a very important parameter which can have huge impact on the aerodynamic results. Thus it is essential to consider model deformations in wind tunnel tests. In this paper, Wing deformations of a high aspect ratio aircraft semi-span model were measured by the Stereo Pattern Tracking (SPT) system in the European Transonic Windtunnel (ETW). The principle of the system is to simultaneously track a total of 40 markers attached on the wing lower surface of the model from two directions by calibrated cameras that were mounted in the inner test section sidewall. Based on wind-off reference measurements over the entire incidence range of the model, the system can identify the displacement between loaded and unloaded conditions, which then can be finally transformed into wing bending and twist information. For the illumination of the SPT markers LED lights were installed at several positions in the test section. The estimated measurements accuracy is better than 0.1mm for wing bending and 0.1deg for wing twist. Aeroelastic bending and twist on the wing were measured for different test configurations. These data are reported that wing bending and twist deformations are raising rapidly as the lift increases when pitching the model up. Wing deformations also change significantly by the dynamic pressure variation, while they have little change with the increase of pure Reynolds number under constant dynamic pressure. The effects on model aerodynamic coefficient of tested configuration from wing bending and twist deformations are also discussed.