Bindel 



reversed and have a greater amplitude than without oscillation of the blades, 

 thus leading to increased drawbacks. Finally, the choice of the amplitude y 

 is a compromise resulting from the estimation of the various dangers encoun- 

 tered by the propeller. 



Third, as stated above, if the length of the sections is not negligible (which 

 is generally the case for the propellers concerned), the sections are sensitive 

 not only to the mean incidence of the flow but also to its camber, i.e., to the in- 

 cidence of the flow along all the sections. In particular, it is not evident that 

 the oscillation of the blade ought to be in phase with the variation of the flow 

 incidence at the mean station of the section. 



Regarding the application, the oscillating-bladed propellers raise some 

 problems which it is not our purpose to deal with in this paper. However, we 

 shall notice that the hub diameter ratio is necessarily larger than in the case 

 of fixed-bladed propellers, due to the necessity of housing the oscillation 

 mechanism system. Likewise, the shape of the blade root will resemble that 

 of the controllable pitch. 



CONDITIONS OF THE EXPERIMENTS 



Initially, it was planned to test several propellers of different types, but, 

 due to a lack of time, it was unfortunately not possible to test more than one 

 propeller. 



This propeller, number 2133, a photograph of which is given in Fig. 3, is 

 the propeller of an escort vessel. It was chosen because it was originally a 

 controllable -pitch propeller, although its nominal pitch was not high. Its char- 

 acteristics are the following: 



- Number of blades: 4 



- Hub diameter ratio: 0.345 



- Blade area ratio: 0.628 



- Effective pitch in nominal conditions: 0.89 



- Diameter of the model: 0.200. 



It was tested in the cavitation tunnel of Bassin d'Essais des Carenes under 

 the following conditions: 



- Inclination 6 of the shaft: 10° and 15° 



- Amplitude of oscillation y of the blades: and ±3° 



- Phase of the oscillation relative to the incidence variation at the mean 

 line of the blade: and +30° (oscillation in advance) 



- Speed of the flow in the tunnel: 3 m/sec 



- Air-content ratio of the water at atmospheric pressure: 0.3. 



For each condition of inclination of the shaft, and of amplitude and phase of 

 the oscillation, visual observations were made first in order to determine the 

 curves (cr versus J, where o- is the cavitation parameter based on the velocity 

 V) of inception of the different types of cavitation encountered, and secondly, 



1504 



