Hadler and He eke r 

 Similarly, the horizontal force and moment coefficients are 



- M^x = [(a + b) Mj^^ - b Mgyl/a. 



If the moments are divided by the thrust, the x and y distances to the point 

 of application are obtained. These distances are nondimensionalized with re- 

 spect to the propeller diameter, thus 



^h = Mzx/T.D. , 



% = Mzy/TD. 



CALIBRATION PROCEDURE 



From the foregoing description it is seen that the force and moment in 

 either the vertical or horizontal plane can be computed if the moments in 

 Planes A and B are known. Hence, the calibration procedure must relate these 

 moments to the output of the strain-gage bridge circuits. The calibrations in- 

 volve two steps, first, the exact axial location of each strain gage must be es- 

 tablished, and, second, the slope of the calibration curve is established. 



Establishing the center of the strain- gage grids was done by mounting a 

 calibrating arm on the shaft with the short leg in the plane of the propeller and 

 the long leg extending back past Planes A and B (see Fig. A4). 



With the calibrating arm in place, but no additional weight, the two gages in 

 the same transverse plane (either horizontal or vertical) are zeroed. A nominal 

 force, or weight (5 lb.) is then imposed on the long leg of the calibrating arm. 

 The weight is then moved toward Plane A until the output of the A gage is zero. 

 This location is then marked as the center of the gage grid at Plane A. The out- 

 put of gage B is also recorded. 



Plane B is then established by moving the weight until the output of gage B 

 is zero. The location of Plane B is then marked, and the output of gage A is 

 recorded. 



Note 1. If the outputs of gages A and B are not identical, the gage sensitivity 

 is adjusted until the outputs are the same. This may require going through the 

 above procedure two or three times. 



Note 2. The same procedure is then followed for the horizontal gages but 

 the weight is hung from a "frictionless" pulley. 



The described procedure has established the dimension as indicated in Fig. 

 A2. For this dynamometer, a = 2.19 in. Dimension b is then measured from 

 Plane A to the point of application of the transverse force. For the calibration 

 this was 2.62 in. 



1488 



