Piezo Active Rotor Blade: Challenges and Solutions

Individual Blade Control (IBC) is a promising technology that addresses the challenges of vibration and noise reduction, while simultaneously providing green benefits through reduced power consumption. To achieve these ends, on-blade actuation mechanisms based on active materials are used. Eurocopter has been working for several years on various IBC concepts, such as discrete trailing edge flaps, the direct twist concept and the integrated active trailing edge concept. The principle behind the IBC approach is to minimize vibration by actively changing the blade pitch during the operation. IBC offers several advantages in weight, power consumption and bandwidth compared to hydraulic control systems. In this paper, the basic structural design and analysis principles of the piezo active rotor blade with discrete flaps are presented. Particular emphasis is placed on an overview of the theoretical investigations as well as the structural tests performed during the development of the piezo active rotor blade. Major challenges and corresponding solutions are discussed consecutively. The preliminary dimensioning of the flap module, including the actuator unit has been performed by the use of the parametric model. Influences brought upon by the stiffness of the individual parts and possible performance losses due to friction have been investigated utilizing this model. The most important design targets for the flap module are the high structural stiffness, low friction of the bearings, no mechanical play and finally the low mass of the flap and thus the entire unit. As a continuation of the parametric investigations, finite element analyses have been performed to examine the three-dimensional stress state caused by operating loads (i.e. centrifugal force, lead lag, flapping and torsional moments). As an explanatory example, the analysis performed primarily for the ADASYS blade is used to describe the main challenges and how to overcome these challenges.