10 Trans. Acad. Sci. of St. Louis. 
The general formula for the pitch of the propeller of an air- 
ship is 
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); 7 is the radius of the propeller; and 7 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. 3 
It is hardly necessary to add that if there are two or more 
propellers, the pitch of the blades should in every case be- 
in which the values of 7 and v may 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 Marcu 14, 1908. 
