2 Modal Model Validation Using 3D SLDV, Geometry Scanning and FEM of a Multi-Purpose Drone Propeller Blade 17 resulted in an impact force of 10 N in this case. The waiting time in-between impacts is set at 2 s, which is more than enough time to let the propeller freely vibrate until its motion completely fades out, and a higher value than the measurement time block. A positive slope pre-trigger of 1% of the input power threshold and starting at 5% of the measurement time are set on the input signal. Three averages were demonstrated enough to achieve satisfactory results with the SAM with an acceptable degree of coherence. FFT data has been analyzed with the program PSV after the measurements data and a generally damped SDOF curvefitting was performed on the obtained Frequency Response Functions (FRFs) in order to extract the modal parameters with vModal (Maul-Theet GmbH, Berlin, Germany). 2.3 Materials and Methods: Geometry Scanning, Reverse Engineering and FE Simulation The analytical part of this correlation cycle consisted on several different operations, carried out by combining different software packages. The first step was scanning the entire propeller surface, up to the pinhole, with an ATOS Triple Scan II (GOM mbh; Braunschweig, Germany) 3D geometry scanner. The propeller was constrained with the same clamp shown in Fig. 2.3 and fixed to a turntable. The working principle of this kind of geometry scanner is not described here for brevity, but can be consulted in [11] among other works. The software ATOS Professional, by the same manufacturer, was used to collect 39 geometry scans from different angles and process them together to generate a triangulated point cloud (Fig. 2.5). Further operations were carried out by the program to repair small holes and seams in the triangulated grid, typical of scans in complex geometries with hard edges. Fig. 2.5 Idealized display of the 39 geometry scans used for the generation of the triangulated points cloud. The blade was clamped to a turntable, which allowed the rotation of the propeller blade for its scan
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