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 PAT propeller that was developed for solving such a problem.
Conventional propeller
PAI propeller
Photo.5 Water streams over the model propeller's blade made visible
by means of oil film method
Figure 4 shows the pressure distributions over the blade surface obtained by calculations for the PAI propeller in a full line and for conventional propeller in a broken line. The difference is seen in the slopes of the pressure distribution on the trailing edge. With PAT propeller there is a wider area of positive pressure over the pressure side, besides with non-existence of the negative pressure peak on the leading edge which is usually seen with conventional propeller.
It could accordingly be said that PAI propeller has solved the problem of separation of water streams which has been an inevitable unfavourable phenomenon characteristic of smaller blade
