## 1 Introduction
The publication provides detailed description of the coupling procedure and the validity of this new aeroelastic tool is checked through a comparison of blade loads at specific spanwise positions, power generation, and blade tip deflection against the respective results of rigid blades. The benchmark comparisons are confined to simple axial flow cases of the NREL 5 MW reference wind turbine [23]. In [24], a standard AL implementation on an incompressible RANS solver is two-way coupled with a finite differences discretization of the 1 st order Euler-Bernouli beam model. Root flapwise moment and tip deflection on axial flow cases of the NREL 5 MW are compared against standard BEM results obtained using FAST [25]. Furthermore, fatigue analysis is performed for two-staggered rotors that operate inside the atmospheric boundary layer. In [26], an OpenFOAM implementation of AL is coupled with a simplified 1 st order representation of the rotating beam dynamic equations. Performance analysis results and blade tip displacements on axial flow cases of NREL 5 MW are compared against NREL reference data (extracted using FAST) and results by other researchers. Recently, in [27], a larger scale WT rotor (DTU 10 MW reference wind turbine [28]) was used as a test model of a loose coupling between EllipSys3D and Flex5. Steady-state performance and damage equivalent loads of the elastic AL model are compared against those obtained by an Actuator Disk (AD) model and the standard BEM model. As far as helicopter rotors are concerned, the AL developments found in the literature focus on pure aerodynamic analysis. At least to the author's knowledge, no publications have dealt with aeroelastic simulations of helicopter rotors by applying AL as the aerodynamic tool. In the present work, an AL aerodynamic model is integrated within a multi body structural dynamics environment for the unified treatment of rotorcraft applications exceeding the context of wind energy applications. Most of the previous aeroelastic developments using AL aerodynamic options, are based on simplified structural dynamic models or linear modal representations. The herein proposed model employs high level of fidelity also in the modeling of the structural dynamics. The multibody model used considers flexible components as non-linearly inter-connected beams (application of nonlinear constraint equations) which are numerically treated in the context of FEM analysis. The above model accounts for non-linear geometric and inertial effects due to large deflections while they can incorporate in the analysis the full structure of the simulated configuration (e.g., wind turbine tower or rotor pylon and other flexible elements of the hub and control chain). The objective of this paper is to assess the accuracy of the AL aerodynamic model in strong coupling with the above described structural dynamics module, by comparing its results with lower fidelity aerodynamic models or experimental data. Two different rotorcraft application examples are considered: (a) WT rotor and (b) Helicopter MR. In order to assess the effect of various numerical parameters on loads prediction, any engineering correction model that needs case specific tuning (e.g., tip correction models) is neglected and the numerical parameters that affect the produced results in a more generic way are investigated in detail. A new way to define the projection width of the calculated aerodynamic forces is proposed, which leads to a straightforward grid independent solution. The test cases considered in the WT analyses extend from simple axial to asymmetric, yaw misaligned flow conditions. Existing literature on AL aeroelastic analyses solely deals with axial flow conditions while yaw misaligned flows are neglected. Recent developments in wind farm control propose wake deflection strategies [29] as an effective approach for increasing power performance and reducing loads.