Generally, with the reduction of blade area ratio, the efficiency will be improved due to the frictional resistance being reduced in accordance with the reduction of the blade area. On the other hand, however, it will be necessary for the blade thickness to be increased in order to compensate the reduced blade width, as the result of which the blade section will necessarily be made fat. With such a blade section shape, the pressure recovery on the trailing edge will be made rapid inevitably; whereby the water streams could not follow the blade movement and will be separated from the blade surface, the separation phenomenon. Photograph 5 shows an example of the water streams over the model propeller's blade made visible by means of oil film method. Conventional propeller blade is on the left hand, while PAI propeller's blade developed by us is on the right hand. You can see the separation phenomenon at the conventional blade on the trailing edge for a wider range. With the water streams over the blade surface being separated, the pressure distribution will be changed, and various adverse influences will be given on, for example, the propeller pitch in a sense of hydrodynamics, and others. It is the PAI propeller that was developed for solving such a problem.
Phot.5 water streams over the model propeller's blade made visible by means of oil film method
