Advanced optical rotor blade deformation measurements on a flying helicopter

Kurzfassung

The performance of a helicopter mainly depends on the design of the main rotor. Thus, the main rotor blades should have an optimised lift distribution for the most likely (favourable) flight conditions. They have to endure strong centrifugal and lift forces and should be able to transmit these loads to the rotor hub and therefore to the airframe. To design light weight rotor blades which could fulfil these requirements, the loads occurring under flight conditions and the resultant behaviour of the rotor blades (bend, twist) have to be known. The in-flight investigation of the deformation of the fast spinning rotor is a demanding task. It is evident, that conventional methods such as strain gauges and accelerometers are difficult to use because of problems with their installation, wiring, the data transmission, and the balancing of the propeller. Additionally, such sensors provide data only at the location where they have been installed. Consequently, a non-intrusive and planar measurement of the rotor blade deformation in flight is of high interest. This need for advanced, non-intrusive e.g. optical measurement techniques has been defined and goal-oriented scheduled as a task of the EC-funded specific targeted research project “AIM – Advanced In-flight Measurement Techniques”. DLR and Eurocopter Deutschland GmbH are applying the Quantitative Video Technique (QVT) together with the Image Pattern Correlation Technique (IPCT) to obtain the in-flight deformation of the main rotor blades of an EC-135. These advanced measurement techniques deliver 3D shape and deformation results by using stereoscopic camera pictures of the investigated objects, in this case, the EC-135 main rotor blades.