**Author details**

Paternoster A.

18 Will-be-set-by-IN-TECH

The relevance of piezoelectric actuators for active blade systems comes from the large specific work they can output [41] while being small and easily integrable. Moreover their reliability

Many actuation systems for the active trailing-egde rotorblade are actuated using amplified stack actuators [33, 44, 56]. Other designs use piezoelectric patch actuators bonded onto a beam [28] or piezoelectric shear actuators built as a torsional actuator as shown in Figure 15

Some studies on the design of airfoils with controllable camber involve stack actuators inside a structure that convert and amplify the motion into a change of curvature of the airfoil [19, 20]. For the deployment of the Gurney flap at the trailing edge, bimorph piezoelectric actuation mechanisms are being studied [59], as well as more complex structures to amplify the displacement of piezoelectric patch actuators and MFCs [42]. AFC and MFC actuators have also been tested successfully for the active-twist application [65]. They provide distributed strain over all the rotorblade surface to successfully twist the blade under operating conditions

Research on flow control systems has considered piezoelectric diaphragms to deliver enough

Today's helicopters are the results of some tremendous work and collaborations in mechanical engineering and aeronautics. The first successes came from inventors that could understand the complexity of a rotating lift surface while designing advanced mechanical mechanisms. To further improve today's helicopters, research is focussing on active blade systems to adapt the aerodynamic properties of the blade to the local aerodynamic conditions. Two aspects are especially studied: enhancing the lift on the retreating side and alleviating the large vibrations in the rotor. Both these aspects will provide improvements on the helicopter performances. Besides the efficiency of the rotor system, the objective is to push the flight envelope of these

Many active concepts are being studied but they all face a large number of challenges to be successfully integrated within a helicopter blade. The rotation speed generates critical loads on the blade and any system within it. With the helicopter blade being the component providing both lift and control in a helicopter, any mechanism influencing its behaviour is required to be durable, reliable and safe. Actuation of the active system is the most critical aspect of a smart adaptive blade. Piezoelectric actuators have the potential to provide compelling actuation for these systems. They are actively tested for many of these concepts. Their toughness, size and reliability make them especial candidates for delivering the required

The key aspect of helicopter progress remains in the collaboration between partners from various domains, combinig different skills and expertise, to answer these challenges and

airflow speed for synthetic jets and achieve proper flow control [31, 67].

aircrafts and to make them faster, smoother and quieter.

makes them suitable for safely powering mechanisms in smart blade concepts.

**4.7. Applications**

[12].

[46, 50].

**5. Conclusion**

mechanical power.

develop tomorrow's aircrafts.

*Chair of Applied Mechanics, Faculty of Engineering Technology, University of Twente, Enschede, The Netherlands*

*Chair of Production Technology, Faculty of Engineering Technology, University of Twente, Enschede, The Netherlands*

Loendersloot R. and de Boer A.

*Chair of Applied Mechanics, Faculty of Engineering Technology, University of Twente, Enschede, The Netherlands*

#### Akkerman R.

*Chair of Production Technology, Faculty of Engineering Technology, University of Twente, Enschede, The Netherlands*
