AIR PERFORMANCE 



171 



value, we observe that it occurs where (P p - P) is a maximum. 

 A measurement of the vertical distance between the P p and P 

 curves shows at once that the maximum is at V = 71. 



' Cmax = 33,000 



248 - 117 

 5700 



758 feet per minute. 



Also this maximum rate of climb occurs at a speed of 71 

 miles per hour. 



Example (7). Rate of Climb {Second Approximation). 

 Taking the same data as in example (6), and taking points at 

 values of V of 55, 60, 70, 80, and 90 : 



The plotting of C on V (which there is no need to reproduce 

 here) gives 



C max = 744 feet per minute. 



Also this maximum rate of climb occurs at a speed of 74 

 miles per hour. 



In using this method it must be remembered that even a 

 twenty inch slide rule hardly gives the necessary accuracy. 

 Therefore if the x column comes out with too few significant 

 figures the work should be done with a table of logarithms. 



