Hadler and He eke r 

 RECOMMENDATIONS 



The results of the experiments presented in this paper are only the begin- 

 ning of a long chain of research which must be accomplished before this type of 

 propeller can be applied to high-speed high-performance vehicles. Some of the 

 most important of these are listed below. 



1. Scaling of the point of transition from base to fully vented flows must be 

 examined and a method for prediction developed. 



2. High-speed photographs should be taken of the flow at the suction side of 

 the leading edge of the blade as it enters the water in both base-vented and fully 

 vented operating conditions to help guide the development of the theory. 



3. Develop theory for the force and moments on a propeller blade as it en- 

 ters and emerges from the air-water interface. 



4. Measure the time history of lift, drag, and moment on an individual 

 blade, so that we can better understand the forces experienced by the blade and 

 the results can be used to check theory. 



5. Develop a rational hydrodynamic theory for designing this type of pro- 

 peller comparable to that for propellers operating fully submerged. 



6. Examine the vibratory forces produced by a propeller which is experi- 

 encing both cyclic loading and unloading and impact force upon water entry. 



7. Blade strength and fatigue must be investigated for their effect upon 

 performance. 



8. Details of blade section shape should be investigated to obtain sections 

 of adequate strength which will have minimum drag under base -vented condition, 

 reduced magnitude of drop in lift coefficient when fully vented, and will produce 

 minimum impact force when entering the water. 



9. The explanation for the large radial shift in center of loading towards 

 the root when the propeller changes from base-vented to fully vented should be 

 ascertained. 



10. It is necessary to be able to predict the pressure field ahead of the pro- 

 peller in both of its two operating modes so that interaction forces with the 

 vehicle can be estimated. 



ACKNOW LEDGMENTS 



The authors wish to record their appreciation for the valuable assistance 

 rendered by F. W, Puryear, C. E. Shields, and D. E. Crown for their participa- 

 tion in the experimental work and to D, E. Crown and J. G. Peck for their as- 

 sistance in preparing the graphs and curves. We also wish to express our 

 appreciation to the Technical Directorate, particularly. Dr. W. E. Cummins, 

 Head of the Hydromechanics Laboratory, for its support. Grateful thanks are 

 due to Mrs. L. Greenbaum for the careful preparation of the manuscript. 



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