The paper addresses the application of a parametric design process for a flying wing configuration. The multi-disciplinary configuration (MULDICON) is a generic unmanned combat air vehicle (UCAV) developed for research purposes, a further development of the DLR-F19 configuration, which was used for research activities in the scope of the DLR project Mephisto and its predecessors FaUSST and UCAV2010. For the MULDICON, the DLR parametric design process MONA is applied. Special emphasis is placed on the structural modeling with composite material where each layer is modeled and analyzed. Various failure criteria are compared to define suitable constraints for the optimization of the load carrying structure. In contrast to optimize the thickness of composites with global allowable strains, such strategy allows for a detailed analysis of every layer. The number of constraints due to the set-up of every ply is substantially increased compared to the strain allowables but the structural optimization is still applicable. The detailed structural and mass models represent the global stiffness and structural dynamic characteristics of the aircraft. For the loads analysis part of the design process, 9 different mass configurations with a total of 306 maneuvering load cases as well as 336 1-cos gust load cases are taken into account. Furthermore, a new simplified landing impact simulation is introduced to consider 12 landing load cases. All load cases are defined according to regulations like CS-25. Such number of load cases is necessary to cover a sufficient number of flight conditions. For the selection of the design loads for the structural optimization, the essential loads are analyzed for a subset of locations. Together with a parametrized optimization model, the structural optimization is conducted. The result is a weight-optimized structural model for the MULDICON. This entire model allows for the investigation of physics-based effects already at an early stage of the design process.

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Stiffness directions of wing structures are already part of the optimisation in aircraft design. Aircraft like the A350 XWB and the Boeing 787 mainly consist of such composite material, whose stiffness directions can be optimised. To proceed with this stiffness optimisation, the aim of this work is to modify and optimise also the linear stress-strain relation. On that account, the Hooke’s law is exchanged by a multi-linear formulation to analyse any nonlinear elastic structural technology on wing structures. The wing structures, which are used to investigate the nonlinear behaviour, are deduced from a mid-range and a long-range aircraft configuration. These wings are analysed with an extended beam method and coupled with a VLM solution to calculate the aeroelastical loading. The proposed beam method is capable of analysing any multi-linear wing structure technology. A degressive structural behaviour shows up a good potential to reduce the bending moment which is one of the main drivers of the structural weight.

In recent years, load alleviation technologies have been more widely used in transport aircraft. For aircraft already in service, load alleviation can contribute in extending the fatigue life, or enable small configurational changes. If load alleviation is considered in the aircraft design process, the structural mass of the aircraft can be reduced. This paper investigates various maneuver and gust load alleviation algorithms as well as potential future technologies regarding flight operation, turbulence forecast and material science, and it evaluates the mass reduction that can be achieved. In doing so, a long-range transport aircraft was taken as the reference, and the considered load case conditions were 1-cos gusts, maneuvers and quasi-steady landing. Based upon the loads, the composite structure of the lifting surfaces was optimized, while the secondary masses as well as the wing planform were kept unchanged. With all technologies implemented, a reduction of the wing box mass by 26.5% or 4.4% of the operating empty mass could be achieved.

Gust load alleviation (GLA) can reduce the maximum loads encountered by airplanes, allowing the structure to be designed lighter, thus saving fuel. Active GLA therefore represents an important subarea in the research of energy-efficient passenger airplanes. However, from a flight dynamics perspective, there are no publicly available simulation environments that allow for an efficient and modular investigation of different technologies like novel GLA controllers or novel flow actuators. Therefore, this paper presents such a simulation environment. The presented aeroelastic flight dynamics model is based on indicial functions combined with a dynamic stall model to predict the unsteady aerodynamics similar to a strip theory approach, while the downwash is considered using a nonlinear steady lifting line method. The structural dynamics are based on the mode displacement method and coupled with the aerodynamics model using constant transformation matrices as well as nonlinear transformations for the inflow. A comparison of the presented model with unsteady Reynolds-Averaged Navier-Stokes simulations shows good agreement for a selected gust case. The presented simulation model is parameterized as an energy-efficient passenger airplane with a light-weight wing sizing by reducing the limit loads from 2.5 g to 2.0 g for equivalent pull-up maneuvers. Open-loop gust load envelopes are presented and discussed for the energy-efficient airplane with different model settings, e.g. with and without dynamic stall model. The source code of the simulation modules is available at: https://github.com/iff-gsc/se2a_aviation_2023.