This study describes an experimental study on dynamic characteristics improvement of a helicopter hingeless rotor system in the viewpoint of aeroelastic stability improvement and low vibration. To do this work, a baseline hingeless hub system and blade were developed. For the study of aeroelastic stability improvement, a baseline hingeless hub system was developed and composite materials have been applied to improve the aeroelastic stability and to reduce the weight of the rotor hub system. For the study of a low-vibration blade, a baseline rotor blade was developed and composite materials have been applied to a well-tailored design focused on optimization of the blade sectional property distribution. In this experimental study, some parts of a baseline hub system were replaced with composite parts to improve the aeroelastic stability. In addition to this aeroelastic improvement of the rotor system, a weight reduction effect was also achieved of about 56%. To verify this aeroelastic stability improvement, hover and windtunnel tests were performed. An improvement of the aeroelastic stability was achieved at about 30%. In addition, a low-vibration small-scale blade was developed by the applying a composite material tailoring method to adjust the mass distribution along the blade. A small-scale blade was designed and tested to verify the low-vibratory characteristics comparison with an existing baseline blade. The improvement of vibration reduction was noted to be about 10-20%.
Finite element analysis for thick composite structures is rather complicated. Two-dimensional modeling, which is relatively easy to make, can cause inaccurate result since the plane stress condition cannot be applied, while three-dimensional modeling is hard to make. In the three- dimensional modeling, it is difficult to model all the layers with different material properties and ply orientation in the structure. In this paper, an equivalent modeling is proposed and numerically tested for analysis of thick composite structures. The method has been verified for the modeling of
composite plate and circular composite tube in order to find their bending deflection and natural frequency. MSC/NASTRAN and PATRAN are used for the calculation. It has been confirmed that three-dimensional analysis must be conducted for thick structures and the equivalent modeling is proven to be accurate when layers with same characteristics are properly grouped.
The proposed modeling technique has been applied to analyze hingeless composite rotor hub system designed by Korea Aerospace Research Institute (KARI). Detailed three-dimensional modeling for this structure is almost impossible to make due to its complex geometry of thick composite structures. Using the proposed equivalent modeling technique, failure analysis was performed based on stress/strain criterion and the safety of each part was checked. Deflection of the
hub system was validated comparing with the result from the simple analytical beam model, and the numerical result will be used for the next design cycle of the composite hub system.
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