which data were presented during the periodic pitching runs was generally 

 within 0.02 degree of the target ij;. For runs in waves without hull 

 pitching, the selection of a propeller revolution at a specified instan- 

 taneous water level within the wave necessitated a tolerance of 5 mm 

 (0.20 in.) of the target water level. 



Considering all sources of error including deviations during a run 

 and inaccuracies in setting conditions, the model scale forces and 

 moments presented in this paper are generally considered to be accurate 

 to within (plus or minus) the following variations: 



"max ^ %AX 



N (lb) N (lb) N-m (in- lb) N-m (in-lb) 



Calm water without 0.4 (0.1) 0.9 (0.2) 0.02 (0.2) 0.05 (3.4) 

 hull pitching 



Pitching and/or 0.9 (0.2) 1.8 (0.4) 0.05 (0.4) 0.09 (0.8) 

 waves 



The values are somewhat more accurate for the runs in calm water 

 without pitching than for runs with pitching and/or waves, because the 

 experimental conditions could be controlled more precisely for runs in 

 calm water without waves and the measured forces and moments were aver- 

 aged over many more revolutions of the propeller. The time-average 

 values per revolution (based on 90 samples per revolution) are slightly 

 more accurate than the maximum values (based on one sample per revolu- 

 tion) which took into account the variation with blade angular position. 

 Further, the peak values may have been slightly influenced by the dyna- 

 mic response of the flexures. 



III. DISCUSSION OF EXPERIMENTAL RESULTS 



A. Loading Components 



The basic loading components are shown in Figure 2. For a right- 

 hand propeller, as used in this case, the sign convention follows the 

 conventional right-hand rule with right-hand Cartesian coordinate 

 system. 



Each component of loading is represented as a variation of the in- 

 stantaneous values with blade angular position, 9, and as a Fourier 

 series in blade angular position in the following form: 



N 

 E 

 n=l 



F,M(0) = (F,M) + E (F.M)^ cosCnG - ((j.^ ^^)^} (1) 



