The phenomenon of brownout is characterized by the rapid evolution of a dense dust cloud around a rotorcraft when it takes off or lands on terrain covered with loose sediment. In an effort to better understand brownout-related problems, the effects of various operational and design factors such as the weight of the rotorcraft, main rotor disk loading, blade loading coefficient, tip speed, rotational frequency, number of blades, and number of rotors were considered to determine possible correlations to dust cloud intensity and/or to the rapidity at which such dust clouds develop. A large collection of public domain photographs and videography of helicopters and tiltrotors encountering brownout were used to assess levels of brownout severity. While the study was subjective and certainly not fully encompassing, factors that appear to correlate to the development of brownout clouds are the average downwash velocities in the rotor wake, the blade tip vortex strengths (i.e., their circulation and vorticity distributions), the total strength of the vortical wake (i.e., the net circulation), and the effective frequency at which the rotor wake vorticity impinges on the ground. While downwash and wake strength inevitably have interdependent effects on the flow field, both factors generally seem to correlate to the intensity of brownout as well as to the radial and vertical extent of the developing dust clouds. The rotational speed of the rotor and the number of blades combine to produce an effective frequency of wake convection, this parameter appearing to correlate to the rapidity at which such dust clouds develop.


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    Titel :

    Assessment of rotorcraft brownout severity in terms of rotor design parameters


    Weitere Titelangaben:

    Bewertung der Intensität der Staubwolkenbildung bei Drehflüglern in Form von Rotorentwurfsparametern


    Beteiligte:

    Erschienen in:

    Erscheinungsdatum :

    2010


    Format / Umfang :

    9 Seiten, 12 Bilder, 17 Quellen




    Medientyp :

    Aufsatz (Zeitschrift)


    Format :

    Print


    Sprache :

    Englisch





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