Concept, Development and Testing of an Experimental Device for Whirl Flutter Research

This work presents the design, development and testing of a small-scale unpowered experimental facility constituted by a multi-bladed propeller, an inertial simulating shaft and a tuning stiffness mechanism. The purpose of this laboratory device is to investigate the test facility modal characteristics concerning the pitch and yaw mode shapes in the case of a fixed propeller and verify the onset of the whirl motion when considering propeller rotation. The data are collected through Experimental and Operational Modal Analyses by distinguishing the backward and forward whirl modes. Through Finite Element analysis employing a onedimensional elements model of the demonstrator, a good numerical-experimental correlation is achieved. Based on the experimentally and numerically data stored for different types of propellers, the influence of the propeller, the shaft inertia and stiffness parameters on the phenomenon is defined, matching current airworthiness rules for propeller-driven aircraft. The discussion concludes with the definition of an experimental stability boundary diagram, identifying for which speed conditions the shaft-propeller system is free from flutter by varying the stiffness of the device