Design, Manufacturing and Identification of an Actively Controlled Flexible Wing for Subsonic Wind Tunnel Testing

Abstract

To minimize the climate impact of commercial flight, aircraft emissions have to be significantly reduced. Important contributions towards this goal are the reduction both of aircraft drag and of structural mass. An increase of wing aspect ratio is a well-known design measure to reduce induced drag, however, a higher wing span usually leads to higher wing mass because of increased structural loads. Thus, load alleviation is essential for the realization of high aspect ratio wings, active gust load alleviation being a promising step to further decrease sizing loads. The paper presents the design, manufacturing and testing of an actively controlled wing in the German Aerospace Center (DLR) project oLAF (optimized load adaptive wing). A wing of 1.75m semi-span is designed and built, equipped with five trailing edge devices (flaperons/ailerons) and two spoilers. The sensors built into in the wing include 12 accelerometers, 10 pressure sensors and a fiber-optical sensor for strain measurements. Furthermore, the forces and moments of a piezo-balance in the wind tunnel mounting are available for feedback, and a marker-based optical measurement system is used for the high-speed tracking of wing and control surface deflections. The wind tunnel campaign takes place at the DNW-NWB subsonic wind tunnel in Braunschweig, a tunnel belonging to the German and Dutch Wind Tunnel organization. The wind tunnel has a cross section of 3.25m x 2.8m and is operating at a maximum flow speed of 90m/s. For the experiment, a gust generator is specifically designed, based on four stationary airfoil vanes, each followed by a downstream rotating, slotted cylinder (RSC) mounted vertically. Load control is implemented on a real-time environment based on control laws being developed in MATLAB/Simulink. The design of the wing, as well as that of the gust generator, is supported by comprehensive numerical studies. The wind tunnel model structure is designed, manufactured and equipped using our in-house aeroelastic model design process. The transfer functions of the actuators, required for the control design, are identified in a specific set-up on the model. The dynamic properties of the model structure are identified both wind-off in a standard ground vibration test (GVT), and wind-on at specific test points for identification. The paper focuses on the design and construction of the wing. Separate papers will give a specific view on design and analysis of the gust generator, as well as on the design of the control laws, and an overview of the test matrix, the data acquisition systems and control hardware, and finally of the experimental results.