AIR PERFORMANCE 49 



and we see from Chapter IV., page 34, that the two points are 

 related by the equations 



and P' = _L. P . . . . (2) 



*J<i 



Now we may consider the point P', V as being on the con- 

 stant torque propeller performance curve at the altitude : for this 

 purpose we will call it P T ', V T ' : corresponding to it in standard 

 density air there is a point P T , V T , related to it by the equations 



V' = 



and 



as we see from Chapter III., page 19. 

 Also, as we have indicated above 



V T ' = V ..... (5) 

 and P T ' = P' . (6) 



= P'-^L from (6) 

 W<7i 



P Jo- 

 ~ from (2) 



Again, V T = V T '^i from (3) 



= V-j= from (5) 

 = 7= -S= from CO 



/r \ / V \ 

 Comparing equations \-jjfj and {yj we see that 



