Cup Anemometer 



IS 



APPENDIX 



Experimental Procedure 



The wind tunnel tests were conducted in a routine manner in the 5 ft. wind tunnel at Massa- 

 chusetts Institute of Technology. The true wind velocity was measured by means of a calibrated 

 side plate while the rotational speed of the anemometer was given by a counter on the anemometer 

 shaft in conjunction with a stop watch. These tests could be made at wind velocities up to about 

 40 m/sec. while the slowest velocity available in the tunnel was in the neighbourhood of 4.5 m./sec. 



Due to the importance of the frictional term V§ an attempt was made to determine V§ ex- 

 perimentally in order to check the values given by the formula on page 6. For this purpose a 

 whirling arm was not considered satisfactory and instead a carriage was arranged with a 30 meter 

 run. It was propelled by an endless rope driven by an electric motor such that the speed of the 

 carriage could be varied from zero to 3 m./sec. A considerable number of determinations of V a 

 were made by the use of this simple device. These, however, showed considerable irregularity 

 but served to indicate that the values obtained by the formula 



V, = 



16T 



?iC„pird 2 D 



were good mean values. 



The dynamic frictional torque T of the bearing and counter used with all the anemometers 

 was found by a dynamometer method to be about .08 gram-meters, and this value has been used 

 throughout for computing V . 



With F known in the formula 



,v /W 



= *. 



the simultaneous equations for the determination of h and k by the Method of Least Squares 



vhere 



zlpnqn = h llqn + c zLq* 

 S^n — h^q n = c-n 



V 



Pn = — {V ~ V,) 



V 



q « = {v - r 9 ) 



c = kJ\. 



The complete results are appended here. 



