Calibration of the two component load dynamometer revealed strong 

 but linear and predictable interactions between the horizontal and 

 vertical force measuring components. So, to obtain forces from tha 

 measured voltages, the following matrix equation was used: 



/ d > 



yx 



*y 



yy 



(18) 



where 



V and V are the measured horizontal and vertical voltages, 

 x y 3 



respectively, in millivolts. From the calibrations, the interaction 

 coefficients were determined to be 



a = 0.1854 pounds/millivolt 



a =-0.0616 pounds/millivolt 

 xy v 



a - 0.1876 pounds/millivolt 



yy 



a =-0.0632 pounds/millivolt 

 yx r 



Dynariic calibrations with mo model attached to the dynamometer revealed 

 significant tare loads above 1.5 hertz. The tare loads due to inertia 

 in the dynamometer increased with frequency but remained 180 degrees 

 out-of -phase with the displacement. 



Under oscillating conditions with the models attached, the measured 

 horizontal and vertical voltages remained in phase with each other, 

 although their phase relationships to the displacement varied with dif- 

 ferent conditions. As a result, the following equations were used to 

 remove the tare voltages from the measured voltages to obtain corrected 

 dynamic voltage amplitudes. 



V dx = Km 2 s1 " 2 + < V xm cos ° * V 2 J 



1/2 



(19) 



26 



