Miller 



>- 0.28 



0.4 0.5 0.6 0.7 0.8 

 Nondimensional Radius, ''/R 



Fig. 18 - Harmonic analysis of 

 four-cycle wake 



These simple wakes were used in all the water-tunnel tests because the ob- 

 jective was to obtain a better understanding of the influence of the parameters 

 affecting unsteady forces rather than to model full-scale conditions and deter- 

 mine unsteady full-scale vibratory forces as is usually done in the unsteady 

 tests conducted with models in the towing basin. 



Two series of tests have been completed in the water tunnel. The first was 

 an investigation of the effects of blade width and skew on the unsteady forces and 

 moments of three-bladed propellers when operating in three- and four-cycle 

 wakes. Some of these results have been used in Refs. (11) and (12) for compar- 

 ison with theoretical methods. The propellers (Fig. 19) had expanded area ra- 

 tios of 0.30, 0.60, and 1.20 with no skew and 0.60 with skew equal to the blade 

 spacing. All were designed for the same operating conditions. The second se- 

 ries of tests used the tandem set of two three-bladed propellers shown in Fig. 20. 

 Each propeller of the set had an expanded area ratio of 0.30 and the set was 

 tested in the three-cycle wake with the blades set at a series of different angles 

 relative to each other. All propellers were 12 inches in diameter. Unsteady 

 forces and moments and their phase angles were determined over a range of 

 loading extending from zero thrust to about twice design thrust. 



272 



