10 Trans. Acad. Sci. of St. Louis. 



The general formula for the pitch of the propeller of an air- 

 ship is 



16 22F 



s=U^i:^lL [XV] 



in which V is the speed of the ship (in still air) in miles per hour; 

 P is the resistance to the ship's motion (or the thrust of the pro- 

 peller); r is the radius of the propeller; and T is the number of 

 revolutions of the propeller per second. 



All helicoidal surfaces should be as accurate and as smooth as 

 possible on both sides of the blades. 



It seems reasonable that the number and axial depth of the 

 blades should be such that no air would pass the propeller with- 

 out being directly acted upon by the propeller, in other words 

 the projection of all the blades on a plane normal to the axis 

 should make a complete circle. That is however a matter to be 

 experimented upon. 



It is hardly necessary to add that if there are two or more 



V ~\~ v' 

 propellers, the pitch of the blades should in every case be — „— 



in which the values of T and v ma}^ not be the same for all pro- 

 pellers. 



While the ideally perfect propeller should be suited to a given 

 set of conditions, it is reasonable to adopt as the given conditions 

 those which obtain when the motor is making its regular working 

 maximum effort. 



Issued March 14, 1908. 



