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Modal Investigation of an Active Twist Helicopter Rotor Blade

Opitz, Steffen and Riemenschneider, Johannes and Monner, Hans Peter (2009) Modal Investigation of an Active Twist Helicopter Rotor Blade. In: CD mit den Proceedings. 20th International Conference on Adaptive Structures and Technologies (ICAST) 2009, 20.-22. Okt. 2009, Hong Kong, China. ISBN 962-85534-5-1

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Abstract

The capability of hovering makes the helicopter one of the most fascinating aircrafts and allows covering a wide range of operational scenarios. The principle of the rotating wings which enables to lift without forward motion is also responsible for the very complex aerodynamic environment of the main rotor. Consequently the main rotor is one of the major sources for helicopter noise and vibra-tion which are diminishing the ride quality and the public acceptance. Being boon and bane at the same time the main rotor is subject to continuous investigations aiming on the improvement of noi-se and vibration characteristics. But due to the combination of strong centrifugal forces and the complex aerodynamics the rotor of a helicopter also presents a very challenging environment for the application of adaptive systems. One opportunity to influence the flow field favorably is the acti-ve rotor control. The idea behind this concept is to superimpose a small blade motion to the prima-ry rotor control. This motion can change the trajectories of the tip vortices to reduce noise or gene-rate additional aerodynamic forces to cancel vibrations of the rotor hub. During the last decades the mechanisms used for active rotor control evolved up to the twist deformation of the rotor blades called Active Twist. The Active Twist rotor blades built at the German Aerospace Center (DLR) incorporate Macro Fiber Composite (MFC) actuators to twist the blade. These piezo ceramic actua-tors are arranged in span-wise segments that can be activated separately. The morphing of the rotor blades is performed with frequencies up to six times the rotational frequency of the rotor. Sin-ce this range already comprises several eigenfrequencies of the blade, the dynamics of the system has to be regarded in order to achieve the intended tip twist. Within this paper the dynamic behavi-or of an Active Twist Rotor Blade will be investigated. Results of an experimental modal analysis in the non-rotating system will be presented. The experimental determination of bending stiffness, torsional stiffness and elastic axis will be shown. The measured blade characteristics will be used to build up a numerical model of the blade. The effects of the centrifugal forces to the eigenmodes and natural frequencies of the system will be elucidated using results from numerical investigations as well as experimental data. Finally the segmented actuation will be used to determine a generali-zed excitation for the first two eigenmodes in torsion. The results of this modal investigation will establish the basis for a modal control of the active twist rotor blade which is planed for the future and will not be presented in this paper.

Item URL in elib:https://elib.dlr.de/60547/
Document Type:Conference or Workshop Item (Speech)
Title:Modal Investigation of an Active Twist Helicopter Rotor Blade
Authors:
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Opitz, SteffenUNSPECIFIEDUNSPECIFIED
Riemenschneider, JohannesUNSPECIFIEDUNSPECIFIED
Monner, Hans PeterUNSPECIFIEDUNSPECIFIED
Date:October 2009
Journal or Publication Title:CD mit den Proceedings
Open Access:No
Gold Open Access:No
In SCOPUS:No
In ISI Web of Science:No
ISBN:962-85534-5-1
Keywords:active twist, modal analysis, dynamics, rotor blade, fan plot
Event Title:20th International Conference on Adaptive Structures and Technologies (ICAST) 2009
Event Location:Hong Kong, China
Event Type:international Conference
Event Dates:20.-22. Okt. 2009
HGF - Research field:Aeronautics, Space and Transport (old)
HGF - Program:Aeronautics
HGF - Program Themes:Rotorcraft (old)
DLR - Research area:Aeronautics
DLR - Program:L RR - Rotorcraft Research
DLR - Research theme (Project):L - The Smart Rotorcraft (old)
Location: Braunschweig
Institutes and Institutions:Institute of Composite Structures and Adaptive Systems > Adaptronics
Deposited By: Ries, Doris
Deposited On:02 Nov 2009 13:08
Last Modified:01 Feb 2011 12:23

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