Str0m-Tejsen and Chislett 



Fig. 10 - Electromagnetic phase-angle cou- 

 pling and synchronous switch arrangement 



Dynamometry and Recording Instrumentation 



Two modular force-gauges are attached to each end of the centre beam 

 (Fig. 11). The physical proportions of the gauges are such that they are flexible 

 in only one direction and they are orientated to pick up either the side force Y 

 or the longitudinal force X. Gimbals, also seen in Fig. 11, bolted to wooden 

 bulkheads ensure that the model behaves as a "simply supported" beam. The 

 model hull, force gauges, and centre beam form a closed loop, eliminating any 

 errors due to friction. Total x and Y forces and N moment acting on the model 

 are obtained from the gauge forces as follows: 



X = Xp + x^ 



Y . Yp + Y^ 



N -- (Yp-Y,H 



(15) 



where the subscripts F and A denote forces measured at forward and aft gauges, 

 and I is the distance from the origin to the gimbal axis (1150 mm). 



The electrical signals from the two X gauges pass through Disa control 

 units, are electrically summed, and then are recorded on a 10-inch-span Philips 

 pen-recorder. The control units are used to adjust sensitivity and zero position 

 and also contain accurate reference (span-check) signals, which can conveniently 

 be regarded as equivalent to known forces at the gauges. When calibrated to- 

 gether with the gauges, these reference signals enable widely differing sensitivi- 

 ties to be used. 



The signals from the Y gauges are processed in one of two alternative ways 

 dependent on the nature of the test. If the planar -motion mechanism is being 



332 



