42 Mr. W. H. Dines. [June 4, 



III. " On the Pressure of Wind on Curved Vanes." By W. H. 

 DINES, B.A. Communicated by the Meteorological Council. 

 Keceived May 14, 1891. 



La June, 1890, a paper* was presented to the Royal Society showing 

 the results of some experiments upon wind pressure upon an inclined 

 surface, and I now give an account of some supplementary work 

 upon the same subject which has been done during the past winter. 



The apparatus was the same as that previously described, with the 

 exception of the actual pressure plate, and precisely the same method 

 of observation has been adopted. 



Instead of a flat wooden plate, a piece of sheet metal 1 foot square 

 has been used, the metal being bent so as to form a portion of a 

 cylinder, the curvature of which was easily varied by drawing the 

 opposite edges more or less together by means of two fine wires. 

 The plate was attached to the lever of the apparatus by about 

 13 in. of 1-in. brass tube, the tube passing a little more than 

 half way across the back of the plate. It is evident that the tube 

 must interfere with the free passage of the air over the back of the 

 plate, but some kind of support behind cannot be avoided. 



In certain positions, experiments could not be made on account of 

 the unsteadiness of the motion, and the consequent fluttering of the 

 sheet metal. There was no trouble in getting the value of the pressure 

 in these positions, but the vibratory motion was often so violent 

 that it tore the metal, almost as though it were paper, and soon 

 rendered the plate useless. These positions are all marked * in the 

 tables ; and the corresponding values are more or less uncertain, 

 because, as soon as the vibrations were apparent, the engine was 

 stopped as quickly as possible to avoid the trouble of having to obtain 

 a new plate. 



As in the preceding paper, 100 has been taken to represent the 

 moment of the pressure upon one sq. ft. exposed normally at 1 ft. from 

 the axis, and all other moments are expressed relatively to this. 



The results obtained are given in the following tables, the diagram 

 at the head of each table showing the form of surface to which it 

 applies. No attempt has been made to eliminate the effect of the 

 eddy from the frame of the apparatus, a full discussion of which will 

 be found in tne paper referred to. The values given also include the 

 pressure upon the supporting arm. This is counterbalanced in the 

 normal position, but must have an increasing effect as the angle of 

 incidence increases, and for this reason it has been considered useless 

 to carry the experiments much beyond an angle of 60 or 70. 



* ' Eov. Soc. Proc.,' vol. 48, p. 233. 



