Assessment of Active Load Control Approaches for Transport Aircraft – Simulation and Wind Tunnel Test

ifasd2024 Tracking Number 141

Active flight load alleviation is an important contribution towards lighter wing structures and wings of higher aspect ratios, both important measures to increase the efficiency of transport aircraft. In the DLR project oLAF (optimal load adaptive aircraft), strategies for active and passive load alleviation are developed and validated. In the project, different lines of investi-gation are followed in parallel – first, a reference configuration of a long-range aircraft is de-signed on a preliminary design basis, and both aerodynamics and structure of the wing are further optimized using coupled CFD- and finite-element-based design methods. Second, various aspects of load control technologies (aeroelastic properties of wings and control devic-es, structural wing design, design of load control algorithms with and without LIDAR) are studied independently, and the results are applied using the design process of the reference aircraft. Third, a closer look it taken at the aerodynamics of spoilers and control surfaces. While spoilers are regularly used as secondary control surfaces, the numerical analysis of de-ployed spoilers and of the efficiency of control surfaces downstream of the spoilers is still challenging. To assess the applicability of spoilers directly for load control as well as the influ-ence of spoilers on the control surfaces, both numerical and experimental investigations are performed. Outputs of the aforementioned activities form the basis for the definition of a wind tunnel experiment for the validation of active load alleviation approaches in the DNW-NWB low speed wind tunnel. The planform of the wind tunnel wing is derived from the overall aircraft design. Aeroelastic tailoring approaches are used for the design of the wing structure, but whereas for a full aircraft, the objective function is optimal performance, i.e. a combination of minimum structural mass and minimum drag, the wind tunnel wing is optimized for maximum deflection and minimum natural frequency to enable real-time testing of active load control approaches. Another important objective of the wind tunnel test is the application of the nu-merical descriptions of spoilers and control surfaces to be used in control design. The active control laws applied in the experiment are derived from the control design approaches devel-oped for the complete aircraft. The results of the wind tunnel experiment are used for the val-idation of the numerical approaches developed in the project. This paper focusses on the specifications of the wind tunnel experiment resulting from the overall project investigations and the contributions of the experiment to the project goals. Fur-ther papers will provide detailed descriptions of the wing design and the wind tunnel experi-ment.