Analysis of helicopter cabin vibrations due to rotor asymmetry and gust encounter

The availability of a numerical tool capable to predict the vibration level inside the cabin due to main rotor-fuselage interaction is of great importance in helicopter design. Indeed, it would be a source of information concerning the fatigue-life of the structure, that in turn would allow a rough estimate of consequent maintenance costs. Furthermore, such a tool would be helpful also in the process of identifying design solutions aimed to the interior noise reduction, that is a crucial aspect for the widely-requested passenger comfort enhancement. In this paper, the simulation tool is obtained as a finite element structural dynamic model of the helicopter fuselage forced by vibratory hub loads, that are predicted through the aeroelastic analysis of the main rotor treated as isolated. In particular, the emphasis is on the evaluation of the incremental vibration level induced by rotor asymmetry and gust encounter, that could give raise to interior acoustic patterns annoying for passengers and to vibration peaks dangerous in terms of structural fatigue. All the results are obtained for two different flight conditions

Aeroelastic identification of a flying uavs by output only data with applications on vibration passive control

This paper shows the capabilities of a system identification approach, based on the experimental measurements of Output-Only, O-O, data, to monitor the aeroelastic characteristics of fixed-wing Unmanned Aerial Vehicles, UAVs, during their actual operative conditions. Traditional Input/Output identification techniques are not easily carried out for aeroelastic systems in operative flight conditions because of the intrinsic difficulty on measuring actual input loads. Therefore, only the response output level should be desirably used for the identification of aeroelastic systems. Then, how the use of the O-O approach allowed to passively reduce the operative aeroelastic vibrations, via piezoelectric-patch devices (PZTs,) mounted aboard the UAV is presented. In order to validate the proposed approach, a preliminary flight test campaign has been carried out. Data recorded aboard the Unmanned Aerial vehicle demonstrated the effectiveness of the PZT patches whose design has been based on the O-O system identification performed in the first part of the present work. © 2010 by the American Institute of Aeronautics and Astronautics, Inc

Aerothermoelastic Response of a Functionally-Graded Aircraft Wing to Heat oads

In this paper, a coupled aerothermoelastic dynamic stability analysis of a functionally-graded composite wing featuring non-classical effects, and immersed in an incompressible gas flow is developed. Specifically, the study concerns the aerothermoelastic stability of aircraft swept wing made of advanced functionally-graded composite materials and exposed to a heat flow generated by a laser beam impacting its deformed surface. The structural model is specialized in the computations to the case of a rectangular, single-layered, swept wing made of functionally graded material (FGM) with a ceramic-metallic-ceramic phase gradient. In particular, aluminun and alumina have been chosen as metallic and ceramic phases respectively. The evaluation of the temperature field on the deformed (actual) configuration of the wing permits to address the problems of the aerothermoelastic response and stability in a coupled framework. As a result, the exact analytical expression of the aerothermoelastic response of the heated wing is obtained in the Laplace space domain and, following this, the static and dynamic aeroelastic instabilities of the wing model are determined. The obtained results indicate that the aeroelastic stability is substantially affected by the thermo-elastic coupling and that the presence of FGM can also significantly influence the aerothermoelastic behavior. Copyright © 2008 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved