Technologietransfer von der Luftfahrt in die Verkehrstechnik: Adaptive Blattverwindung für Hubschrauberrotorblätter - Experimentelle Ergebnisse und Ausblicke.

Abstract

Applying adaptronics to helicopters has a high potential to significantly suppress noise, reduce vibration and increase the overall aerodynamic efficiency. This paper presents recent investiga-tions on a very promising specific concept named Adaptive Blade Twist (ABT). This concept allows to directly control the twist of the helicopter blades by smart adaptive elements and thus to posi-tively influence the main rotor area which is the primary source for helicopter noise and vibration. Since the interaction of non-stationary helicopter aerodynamics and elastomechanical structural characteristics of the helicopter blades causes flight envelope limitations, vibration and noise, a good comprehension of the aerodynamics is essential for the development of structural solutions to effectively influence the local airflow conditions and finally develop the structural concept. Therefore the ABT concept will be presented with respect to these considerations. This concept is based upon the actively controlled tension-torsion-coupling of the structure. For this, an actuator is integrated within a helicopter blade that is made of anisotropic fibre composites material. Driving the actuator results in a local twist of the blade tip, in such a way that the blade can be considered as a torsional actuator. Influencing the blade twist distribution finally results in a higher aerodynamic efficiency. The paper starts with giving a review on conventional concepts and potential adaptive solutions for shape control. Hereafter, some calculations of the adaptive twist control concept are presented. These are based on a representative model in which the active part of the rotor blade is simplified with a thin-walled rectangular beam, that is structurally equivalent to a model rotor blade of the Bo105 with a scaling factor 2.54. The calculations are performed using an expanded Wlassow Theory. The results are valid for static and dynamic conditions. For the dynamic condition exces-sive deformations near the blade resonance frequency shall be utilised. Therefore, the actuated blade section has to be properly designed for this preconditions. This has been demonstrated and verified in experiments which will not be discussed in this paper. For experimental investigations on the ABT concept the skin of the outer part of the model rotor blade was manufactured of fibre composite material using the above mentioned tension-torsion-coupling effect with an additional uncoupling layer between skin and spar. In order to assess the influence of the aerodynamic effects, small scale wind tunnel tests at the RWTH Aachen were made. The experimental results have shown that near to the resonance frequency dynamic forces generate a torsional deformation of ± 1,9 degrees at the blade tip