light-weight, strain-gaged single flexure element. The measured lowest. 
natural frequencies of the three flexures in air were as follows: 
Frequency (hertz) Mode 
Flexure 1 550 M, 
Flexure 2 450 MO 
Flexure 3 282 M, 
The measured amplification factor (ratio of output amplitude to in- 
put amplitude) and phase shift for all three flexures was as follows: 
Frequency Range (hertz) 0 to 60 60 to 120 
Phase Shift (degrees) 0 to 0.05 0.05 to 0.15 
Amplification Factor 1.00 1.00 to 1.05 
In the previous eeperimentd the natural frequency of the flexures 
was found to be reduced by 55 percent when submerged with blades attached. 
As a result, it was concluded that the flexures had a "true" dynamic re- 
sponse up to at least the third harmonic and no greater than a five per- 
cent amplification up to the sixth harmonic. Because the blades used on 
the present experiment were lighter and smaller than those used on the 
previous experiment, it was assumed that the natural frequency of the 
flexures would be reduced to a lesser extent when submerged with blades, 
so that the dynamic amplification would be less. This assumption was 
supported by the increase in frequency of the extraneous signals appearing 
in the unfiltered experimental data as discussed in the experimental re- 
sults section. 
The propeller shaft drive and soft-mount support system were dynam- 
namically loaded in the vertical, longitudinal, and transverse directions 
to obtain the lowest natural frequencies of the system. The natural fre- 
quencies of the system in air were found to be: 
Mode Natural Frequency (hertz) 
Vertical bending W252 
Horizontal bending 6.0 
Axial 4.6 
The support system had a low resonant range; however, the soft- 
mount system was specifically designed to prevent towing-carriage 
13 
