In all rotorcraft, the main rotor is the primary source of helicopter vibration, transmitting aerodynamic and inertial loads to the fuselage at a frequency proportional to the rotor speed. However, simulation of progressive immersion into an idealised sharp-edged gust induces a split around this frequency proportional to the relative velocity between gust and aircraft. To test for this effect in more complicated gust patterns, a realistic operational flowfield was generated using a computational fluid dynamics package. Numerical experiments suggest that a realistic atmospheric environment can be found which induces this split about the fundamental forcing frequency. A simple mathematical expression is derived which also predicts changes in frequency as a function of flight condition. The sensitivity of a class of optimal frequency-tuned active vibration control algorithms (higher harmonic control), to this type of disturbance is found to be poor. Enhancements to the algorithm through the inclusion of a Kalman state estimator and multi-harmonic inputs fail to yield any performance improvement. A novel modification to the algorithm allowing for direct feed forward of a Fourier estimate of the gust is shown to significantly improve controller performance. However accurately estimating the disturbance vector significantly complicates implementation of the technique.


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    Title :

    Helicopter vibration induced by highly structured turbulence


    Additional title:

    Anregung mechanischer Schwingungen eines Helikopters durch hochgradig strukturierte Turbulenz


    Contributors:

    Published in:

    Publication date :

    2003


    Size :

    9 Seiten, 12 Bilder, 1 Tabelle, 22 Quellen



    Type of media :

    Article (Journal)


    Type of material :

    Print


    Language :

    English





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