Study of the propeller with small blades on the blade tips.

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The performance tests of bladelet propellers were experimented about three parameters (bending angle, installaion angle, sweepback angle). As a result, under J=0.4[0.6, which conditions are concerned with real working point in big merchant ships, the efficiency arised 1[3.5% in the advanced constant base, or 3[4% in the <K_t> / <J^2> base, compared with MAU original propeller. The best arrangements of the bladelets are bending angle ( Leading side:45゜, Trailing side:45゜ ), installation angle ( L:-4゜[0゜, T:4゜[6゜ ),and sweepback angle ( L:0゜[20゜, T:15゜ ). Concerning with the distribution of pitch, the more similar that of the bladelet is as that of main blade, the better the efficiency is.From the result of flow visualization of the oil film method concerning the surface of propeller, it is expected that the configuration of aerofoil should be stronger in laminar separation, and the bending angle should be 45゜.By means of the tuft grid method of the wake, the size of tip vortex by the good efficiency bladelet propeller was less than that by the original one, which tells the reduction of induced drag and that of revolving energy.More over the configuration of the wake could be got by Laser Doppler Velocimeter, and the fluctuating pressure showed the less strength of tip vortex by the good bladelet propeller than by the original one. These propellers were calculated by vortex lattice method. But the exact expectaion of these propeller performance could not be got.