Str^m-Tejsen and Chislett 



tan = 



(6) 



where yp is the angular displacement from the tank centre line. Thus the gen- 

 eration of an angular motion and linear motion relative to the carriage results 

 in a pure angular motion of the model relative to the ivater. 



A practical realization of this requirement as adopted in the HyA planar- 

 motion mechanism is diagrammatic ally illustrated in Fig. 6. The arrangement 

 consists of two scotch-yokes connected by a rigid shaft. Rotation of the shaft 

 results in periodic movement perpendicular to the carriage centre line of two 

 points F and A fixed in the model. By variation of the phase angle /. between the 

 forward and aft scotch-yokes, various combinations of angular velocity and 

 movement perpendicular to the carriage centre line are obtained. The phase 

 angle, resulting in the fulfilment of the conditions for pure angular motion of the 

 model relative to the water, is found as follows. Let 



^F'^A ~ lateral displacements relative to the carriage centre line of points 

 F and A fixed in the model, 



d = distance of points F and A from origin of the body-axis system 

 fixed in the model, 



a = amplitude of the scotch-yokes and of the lateral displacement of 

 points F and A, 



Fig. 6 - Motions generated by a 

 planar-motion mechanism 



326 



