The scaling laws in the geometry, velocity, and power for flapping flyers, for example, birds, and fixed-wing aircraft are discussed from a comparative point of view, and the aerodynamic implications of the scaling, particularly on the lift-to-drag ratio, flapping span efficiency, induced drag, parasite drag, and propulsive efficiency are explored. The results shed insights into flapping flight and provide a useful guideline for the preliminary design of a flapping-flight vehicle. The wing aspect ratios for birds and aircraft are 7.83 and 8.15, respectively. Nevertheless, the body length of birds is only about 35% of that of scaled-down aircraft. The ratios between the total wet area and wing area for birds and aircraft are 2.66 and 4.35, respectively. The body fineness ratios for birds and aircraft are 2.97 and 8.52, respectively. From a scaling point of view, the wing loading and cruise velocity of birds are only 58% of those of scaled-down aircraft. As a result, the bird weight is significantly larger than the weight of scaled-down aircraft at the same Reynolds number, indicating that a typical bird has to generate larger lift for cruising flight. The cruise power of birds is about 74% of that of scaled-down aircraft. The estimated maximum lift-to-drag ratios for birds and aircraft are 9.1 and 11.9, respectively. The scaling laws for the power available are given, providing interesting results such as the upper weight limit for bird flight when it is combined with the scaling laws for the required power. Furthermore, the scaling law for the muscle weight of birds is intriguingly close to that for the aeroengine weight. The aerodynamic consequences of the scaling laws are explored based on simple theoretical models. The flapping span efficiency estimated for bird flight is 0.5, which is lower than the Oswald span efficiency (0.6-0.9) of typical aircraft, and therefore it indicates larger induced drag. The estimated induced-drag coefficient based on the wing area for birds is 0.0386 +/- 0.0208, which is much larger than that of propeller/turboprop aircraft. Nonetheless, the estimated mean parasite drag coefficient based on the wing area for birds is 0.0344, which is comparable to that of propeller/turboprop aircraft. Hence, the mean total drag coefficient of birds is 0.073, which is contributed roughly equally by the induced drag and parasite drag, and is much larger than that of typical aircraft. The propulsive efficiency for bird cruise flight is 0.85 +/- 0.51, where the large error margins represent the statistical variation in regression for a heterogeneous group of birds. In summary, birds and aircraft enjoy similarity in some important geometrical quantities. Compared with a scaled-down aircraft, a typical bird cruises at a lower speed with a reasonable propulsive efficiency and manages to overcome larger drag and generate larger lift to support its heavier weight.


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    Titel :

    Comparative scaling of flapping- and fixed-wing flyers


    Weitere Titelangaben:

    Vergleich der Maßstabsgesetze von Schlag- und Festflügelflugzeugen


    Beteiligte:
    Liu, Tianshu (Autor:in)

    Erschienen in:

    AIAA Journal (online) ; 44 , 1 ; 24-33


    Erscheinungsdatum :

    2006


    Format / Umfang :

    10 Seiten, 14 Bilder, 1 Tabelle, 40 Quellen




    Medientyp :

    Aufsatz (Zeitschrift)


    Format :

    Print


    Sprache :

    Englisch