Rotor blade shape reconstruction from strain measurements

Traditional helicopter blades are subject to significant deformations, which influence control forces and moments, as well as the helicopter aeroelastic and aeroacoustic behavior. Thus, the knowledge of rotor elastic states could help improving flight control efficiency, and reducing vibration level and acoustic emissions of next-generation helicopters. This paper presents an original and computationally efficient modal approach aimed at dynamic shape sensing of helicopter rotor blades. It is based on strain measurements in a limited number of points over the blade surface. Although the algorithm is based on the cascaded solution of linear algebraic equations, much like other modal-based algorithms, it is able to reconstruct nonlinear, moderate lag, flap and torsional deflections, which are typical in helicopter structural dynamics. The algorithm is tested on non-rotating and rotating hingeless blades through numerical simulations based upon a multibody dynamics solver for general nonlinear comprehensive aeroelastic analysis. Its capabilities are assessed against those of classical modal approaches. Numerical investigations show that the proposed algorithm is reliable, accurate and robust to measurement noise.