Bindel 



We have also planned to carry out tests with oscillating blades, but in a 

 tanker model. The arrangement consists in providing the rotating blades with 

 pins which slide on a groove inside a cylinder fixed astern. Although this de- 

 vice introduces undue friction, I hoped that the improvement of the efficiency 

 would balance this loss, since not only the change of angle of attack but also the 

 lengthening of the hub will provide (as shown by Dr. Castagneto some years ago) 

 such an improvement. 



Even if the system is not used, this type of test may load to a better under- 

 standing. In this case, it may be interesting, for instance, to see whether an 

 improvement of the propulsive coefficient is attained as a result of lowering the 

 load in front of the stern post. 



REPLY TO DISCUSSION 



S. Bindel 



In reply to the question of Dr. Cox, I should say that the test program indi- 

 cated in the paper is a general outline of some possibilities among which it would 

 be necessary to choose. It seems to me, at this time, that the best option would 

 be to consider one or several "desperate" cases, for which the other methods re- 

 vealed themselves ineffective (cf., for example, Ref. 2 of my paper), and to see 

 if oscillating the blades may lead to an acceptable solution. If so, it would be de- 

 sirable to cover all aspects of the investigation; if not, the system ought to be 

 rejected, at least for inclined propellers. 



I did not give the description of the mechanism used because the paper was 

 primarily concerned with the hydrodynamic aspect of the problem; but the way 

 to build the mechanism is important, of course, as underlined by Mr. Van 

 Gunsteren. On the model, two opposite blades were actuated by a lever con- 

 nected with a piece turning around a fixed cylinder, the axis of which was cross- 

 ing the axis of the propeller. This system was simple; however, I do not think 

 that its complete description would give valuable information on the efforts re- 

 quired for a full scale propeller, due to the fact that the real system would 

 probably be different. 



I agree with Mr. Van Gunsteren that from a hydrodynamic point of view it 

 would be better to place the shaft in the direction of the flow, but in this case 

 the coupling would have to transmit all the propulsive torque, whereas the torque 

 necessary to oscillate the blades is much smaller and the mechanism may be 

 located inside the hub. 



I agree with the suggestion of Mr. Van Gunsteren and Prof. Mazarredo, that 

 the oscillating-bladed propellers would perhaps be best utilized in the case of 

 single screws working in nonuniform flow. I also thought of this application, but 

 so far I have had no time to make any investigation in this direction. 



Finally, I thank very much the contributors for their supplementary infor- 

 mation, their remarks, and their questions. 



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