Evaluation of a Compliant Droop-Nose Morphing Wing Tip via Experimental Tests

A morphing droop-nose wing tip with span of 1.3 m and target 2 deg droop was designed, manufactured, and tested as part of the European project Novel Air Vehicle Configurations: From Fluttering Wings to Morphing Flight. The morphing droop-nose device featured a fiberglass composite skin with optimized three-dimensional thickness distribution, which was supported by topology-optimized superelastic nickel titanium and aluminum internal compliant mechanisms. The tests included ground and low-speed wind-tunnel tests (55  m/s) with the aim of assessing the structural performance and the design chain through measurements of shape, strains, surface pressures, and total forces/moments on the model. Comparisons with the experimental results were used for validation of the computational models and optimization tools. The morphing device was able to change shape while resisting the external loads, and it was identified that the distribution of strain and shape accuracy may be improved through the use of a concurrent as opposed to sequential design chain and other developments to the optimization tools. The use of a superelastic material facilitated the high-strain displacement, exceeding 2% strain in the design case and measured up to 4.54%, making it highly suitable for compliant mechanism applications. This paper explains the insights made from the experimental tests and recommendations for the future design of morphing structures.