**5. Conclusion**

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 aircrafts and to make them faster, smoother and quieter.

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 mechanical power.

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 develop tomorrow's aircrafts.
