Blade Deformation Measurements with IPCT on an EC 135 Helicopter Rotor

Abstract

For the design of a helicopter rotor blade, it is crucial to predict the dynamic behavior and occurring forces and moments. For the validation of prediction tools, reliable flight test data is required. Furthermore, flight test measurements are necessary for the calculation of fatigue loads. Today, strain gauges are applied to a helicopter rotor blade to perform measurements in flight test. Locally, they allow a precise strain measurement for the complete rotor revolution. This instrumentation implies a high effort. Furthermore, wiring can imply difficulties due to its weight and its modification of the aerodynamic shape. An optical measurement technique may overcome some of the limitations of strain gauges. A precise measurement of the deformation of the complete surface of the rotor blade allows to locate high strains and to identify oscillatory modes. The exact blade position can be identified optically. One of these advanced optical measurement techniques is the Image Pattern Correlation Technique (IPCT). Today, IPCT is a state of the art measurement technique for static and dynamic deformations. In AIM, DLR and Eurocopter explore the feasibility of Quantitative Video Technique (QVT) together with the Image Pattern Correlation Technique (IPCT) on the rotating main rotor blades of a flying helicopter. Ground tests of the measurement system on a whirl tower and a tied down helicopter are performed to verify the feasibility and performance of the measurement system previous to flight testing.