EXPERIMENTAL AND ANALYTICAL 

 STUDIES OF PROPELLER-INDUCED 

 APPENDAGE FORCES 



August F. Lehman and Paul Kaplan 

 Oceanics, Inc. 

 Plainview, New York ; ^ ; r--^ ; 



ABSTRACT 



During the past several years experiments involving unsteady forces 

 induced on an appendage by a propeller have been carried out at 

 Oceanics, Inc. Most of these experiments concerned a propeller 

 downstream of an appendage, although certain measurements were 

 made with the propeller upstream (rudder case). An associated theo- 

 retical analysis to predict the influence of various physical parameters 

 on the magnitude of the induced forces was also developed, based upon 

 two-dimensional flow considerations. Two-, three-, and four-bladed 

 propellers were studied, with blades of two thicknesses. The effects of 

 spacing distance between the appendage and the propeller, appendage 

 asymmetry, and the appendage attack angle on the induced forces were 

 of primary interest. This paper presents the more pertinent results of 

 these investigations and discusses a technique of using a single -bladed 

 propeller to predict multibladed propeller induced forces. Limited 

 comparisons between the developed theory and the experimental data 

 are also presented. 



INTRODUCTION 



In evaluating the vibratory characteristics of naval vessels, knowledge of the 

 appendage forces induced by a propeller is important. By the early 1960's theo- 

 retical work (1-5) had for the most part preceded any experimental evaluation of 

 this problem, primarily because of the difficulties of satisfactory unsteady meas- 

 urements. In 1960 Lewis (6) reported on the first successful experimental measure- 

 ments of the transverse or side forces induced on an appendage upstream of a 

 propeller. This initial work was amplified by further published data in 1963 (7). 



In 1964 Oceanics, Inc., was supported by the Naval Ship Research and De- 

 velopment Center on the first of a series of model studies to obtain certain 

 propeller- appendage test data. This first study involved a measurement of both 

 the axial and transverse induced forces; and a series of investigations covering 

 various aspects of this problem followed. The present paper summarizes the 

 pertinent results of those investigations. 



The basic measurements were unsteady axial and transverse fluctuating 

 forces induced on an upstream appendage by a propeller at blade- rate frequency 



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