Loads Analysis and Structural Optimization of a Long-Range Transport Configuration with Hybrid Laminar Flow Control

Abstract

This work elaborates the investigation of a long-range transport configuration with hybrid laminar flow control (HLFC) using an iterative pre-design process featuring loads analysis and structural optimization. The HLFC wing was designed with a 3D transonic inverse method. From the loads perspective, the main changes compared to the turbulent counterpart comprise different profile geometries, additional system masses and a backward shift of the front spar to accommodate those additional systems. In the loads analysis, a total of 216 quasi-steady maneuver, 756 dynamic gust cases and one quasi-steady landing case are considered. For the maneuver simulations, a simple maneuver load alleviation (MLA) is implemented. After the post-processing of the loads to extract the sizing relevant ones, a structural optimization is carried out. The constraints in the optimization are maximum strains, 1D buckling and minimum thicknesses. The objective function is the minimization of mass. The cycle comprising loads analysis and structural optimization is conducted iteratively, until the change structural mass - in this case the wing box mass - between two cycles fulfills a defined convergence criterion. Compared to the turbulent counterpart, the HLFC wing box is 0.82% lighter. However, due the additional system masses, the HLFC variant has 0.37% higher operating empty mass, or 0.20% higher maximum take-off mass. Otherwise, the wing load envelopes of HLFC variant are almost identical to those of the turbulent counterpart in general (1.4% more maximum wing root bending moment, 1.1% less maximum root torsion). In the middle wing part, the HLFC aircraft has slightly more nose-down torsion due to the different wing profiles (ca. 6% more minimum torsion and 3% less maximum torsion at 50% span). As a conclusion, the conducted investigation provides an insight into the potential changes in the loads and masses of the HLFC aircraft. On the overall aircraft design level, further studies regarding the changes in the block fuel for a given flight mission or potential changes in the fuel tank layout due to the different wing box geometry can be carried out.