70 AEROPLANE PERFORMANCE CALCULATIONS 



Now combine these two components graphically on the side- 

 view drawing mentioned above, so as to get the direction of the 

 slip stream. Draw a line in this direction through the centre of 

 the propeller boss to cut the line joining the leading edges of the 

 machine in the side-view drawing at a point A. 



Now turn to the front-view drawing of the machine and 

 mark in the point A. 



With A as centre describe a circle of d inches diameter and 

 use this circle instead of the propeller circle to compute 5'. 



Turn again to the side-view drawing and note the angle of 

 incidence of the wings relative to the resultant slip stream direc- 

 tion. Then look up the corresponding lift coefficient k^ for this 

 angle of attack from the model tests. 



Now W = 'QQ2V[k imax ($ ~ S') + L '(i + 



-V; 



.*. V 



V, of course, is in miles per hour. Therefore the value of v, 

 in feet per second is given by the equation 



