ADHESIVELY BONDED JOINTS OF THE PRIMARY STRUCTURE WITHIN THE HAP PROJECT

<p>In the HAP (High Altitude Platform) project, the German Aerospace Center (DLR) is developing a solar-powered long-range aircraft, various payloads for Earth observation missions, the ground control station and operating concept. The mission conditions and<br> objectives pose major challenges to the aircraft structure, especially with respect to lightweight design. This presentation intrudces the design process of bonded joints for the primary structure on the example of the wing spar, as the most critical component. The wing, with an overall span of 27m, is divided in three wing sections, with the tubular wing spar being assembled from several segments for manufacturing reasons. Considering the demanding lightweight design expectations, adhesively bonded scarfed tubular joints are selected. A manufacturing concept is developed to minimize effort for joint preparation. The dimensioning is based on global (GFEM) and detailed finite element models (DFEM) to fine-tune the design (stiffness discontinuities, surface toughness) to increase the load<br> carrying capacity. This is flanked by physical tests for model validation and material characterization, such as adhesive characterization, to increase DFEM accuracy.</p>