64 



KANSAS UNIVERSITY QUARTERLY. 



Three forms of fans were used: one plane, x Fig. 2, and two 

 curved, y and z, Fig. 2. 



The pull P was found for each speed for four fans; then one fan 

 was taken off and P found for the two highest speeds; then a sec- 

 ond fan was taken off and P found for the four speeds; a third fan 

 Avas then taken off and P found for the two highest speeds; finally 

 all the fans were taken off and P found for friction. 



After thus finding the pull required to drive the fans with con- 

 cave surface forward, that required to run them with the convex 

 surface forward was found in the same way. 



Column one, table I, gives the speed in revolutions per minute 

 of the fans; column two the velocities of center of fans in feet per 

 second. In the other columns are given the net pull in pounds, 

 after slight adjustments. The subscripts x, y, z refer to the curva- 

 ture as shown in Fig. 2; the subscript f measures fan moving with 

 concave surface forward and b convex surface forward. 



TABLE I. 



Fig. 3 shows diagrammatically the relation between the velocity 

 and Px for four fans. The points i, 2, 3 and 4 are very nearly on 

 a parabola whose equation is V-==6. iP^ . 



The following facts are easily deduced from the table: 



(i ) The resistance is Very small for low speeds and nearly inde- 

 pendent of the curvature of fans. 



(2) The resistance to plane surfaces is greater than that to 

 curved ones, the difference increasing with the speed. 



.(3) The difference decreases as the radius of curvature de- 

 creases. 



(4) The resistance to a convex surface is somewhat less than 

 that to a concave one. 



(5) The resistance to the y form of fans, for a fan center veloc- 

 ity of 13.5 feet per second, is 22 per cent, less than that to x form, 

 and the resistance to the z form 34 per cent less. 



(6) The relation between P^ and the number of fans for a given 



