A Complete experimental investigation of gust load: From generation to active control

In order to make substantial progress in reducing the environmental impact of aircraft, one of the key technologies investigated in the framework of the platform SFWA-ITD is the reduction of aircraft weight. This challenge requires the development and the assessment of new technologies and methodologies for both structural design and load control. To achieve the investigation of the specific case of gust load, ONERA had defined a dedicated experimental research program based on three Wind Tunnel Test (WTT) campaigns. To reach these objectives, a new experimental set-up was designed and manufactured through an Aviation Design - ONERA collaboration and is composed of two main components implemented within the ONERA S3Ch transonic Wind Tunnel Facility. The first component, called gust generator, consists of two oscillating airfoils installed upstream of the wind tunnel test section and allows to produce air flow deflections. The second component, the test model, is a 2D supercritical airfoil equipped with a control surface and is based on the well-known 2 degrees-of-freedom (DOF) aeroelastic model (pitch and plunge motions). A first WTT campaign has been carried out to qualify the unsteady flow induced by the gust generator and the ability to generate cylindrical gust field with significant and reproducible amplitudes in subsonic and transonic ranges. The second WTT was devoted to analyse gust effects on the test model behaviour for different structural and aerodynamic conditions. The aeroelastic model behaviour has been therefore characterized in terms of unsteady pressure and structural acceleration fields for both gust perturbations and control surface commands. These results provided the input data for the final WTT aiming at demonstrating the active gust load alleviation thanks to closed-loop control approaches. Real time feedback controls were tested during this WTT up to transonic conditions and have demonstrated significant reductions of the model structural responses to gust.