The signals were then digitized and analyzed by using a Model 70 
Interdata Digital Computer, and then stored in digital form on a nine- 
track magnetic tape. The on-line analysis of the data is discussed in the 
section on data acquisition and analysis. 
CALIBRATION 
Prior to the experiment, each flexure was statically calibrated in 
air to establish flexure sensitivities, interactions, and linearity over 
the loading range of interest. These calibrations were conducted with the 
flexures mounted in a calibration stand, with the flexure electrical ca- 
bles connected through the flywheel and drive assembly as in the experi- 
ment. Each flexure was subjected to independently controlled forces in 
the axial, transverse, and radial directions (i.e., Flo ee and Fo re- 
spectively) and to independently controlled moments about the axial, 
transverse, and radial directions (i.e., M, Bye and M,> respectively); 
see Figure l. 
The static calibration showed that all flexures had a linear re- 
sponse over the load range of interest. Table 2 shows the interaction 
matrix. These calibrations indicated that all flexures had good sensi- 
tivity except Be whose sensitivity was slightly lower than desirable. 
The interactions were small except for the effect of M, on ae The infe- 
rior characteristics of the ER flexure is not considered a serious short- 
coming since Ek arises primarily from centrifugal loading and can be 
analytically calculated. In addition, no significant variation of ES 
with blade angular position was anticipated. Flexure 3, which measured 
F. and M,> was further evaluated by correlation of air-spin experiments 
with analytically calculated results, as discussed later. The interac-— 
tions were taken into consideration during data analysis. 
The flexures used in this experiment had been dynamically cali- 
brated by easy” to determine the frequency range over which unsteady 
forces and moments could be reliably measured. In this procedure, an 
electromagnetic shaker in air was used to apply a relatively constant, 
maximum amplitude, variable-frequency force or moment-excitation in all 
six-component directions to all six flexure elements. The force or mo- 
ment amplitude imposed by the shaker was monitored through an extremely 
12, 
