Wu 



Fig. D3 - The well-propeller 

 in the optimum behind condi- 

 tion (Rj, the flow interaction 

 resistance, equals the resist- 

 ance caused by those fluid 

 particles which will be used 

 for propelling afterward) 



REPLY TO DISCUSSION 



T. Y. Wu 



I wish to thank Professor van Manen and Dr. Schwanecke for their interest- 

 ing comments. Dr. Schwanecke pointed out several promising propulsive de- 

 vices that have been innovated with ingeneous applications of the underlying 

 fluid dynamical principles. In this respect, I may also mention the theoretical 

 studies of A. A. Fejer, of H. R. Kelley, and some full-scale experiments of 

 Glen Bowles. Their studies are concerned with the swimming motion of three 

 hinged plates in two-dimensional oscillations, for which the optimum six de- 

 grees of freedom can be evaluated. In this kind of inventive attempts, I think 

 one can be duly rewarded if the efforts are directed towards extraction of the 

 basic physical principles underlying the phenomenon, rather than imitating na- 

 ture to the very last detail. From bird flying came the innovation of airplanes, 

 which has evolved through decades to supersonic flights, a regime already 

 highly transcending the original level. An effective application of the swimming 



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