| 摘要 |
The invention relates to a boomerang that can automatically change both elevation angle α of blades and curve radius r of blades upon the change of rotary speed of blades (12), wherein blades (12) are made of elastically plastic film preferably selected from a group of polyvinyl chloride, polypropylene, polyethylene terephthalate, polystyrene and high impact polystyrene, the material has a specific weight of from about 0.9 g/cm3 to about 1.60 g/cm3 and as thicknesses of from about 0.1 mm to about 1 mm; the ratio between rear groove deep and blade width is of from about 1/7 to about 6/7; the ratio between front groove deep and blade width is of from about 0 to about 3/7; the elevation angle α0 is of from about 10° to about 45°; the initial curve radius r0 of the blades is longer or equal to ⅕ of the radius R of said ring (13); the ratio between the total area of said blades and the area of a circle defined by said ring (13) is of from about 12.5% to about 38%.
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