AIR PERFORMANCE 53 



the engine is developing/^// revolutions and full indicated torque 

 for the altitude (which we already know from Chapter III., 

 page 19, to be a times the full indicated torque in standard 

 density air). 



Now further, let P T ', V T ' and P R ', V R ' be so related to P', V 

 that 



N ' V ' 



fli. = JLx (i) 



N' V ^ } 



Then it follows from propeller theory that 

 T ' /V V 



-f-(f') 



T ' /V '\ 2 



and ~Y = vvv ' (4) 



Also, of course, L = - J" 7 . (5) 



and -F = ^, y ^ . - (6) 



From (3) and (5) we have 



-($)' - 



and from (4) and (6) we have 



. 



V'/ 



That is to say, that the three points we are considering are 

 connected by the fact that a " Throttling Curve " passes through 

 them. 



In other words we could first choose P', V as any point on 

 the P' curve through which a curve of the family passes, and then 

 read off the values of V T X and V R r by noting the intersections of 

 this same curve of the family with the P T ' and P R X curves. 



Now N R ' = N by definition . . (8) 



N' N' V 

 ' . A^ = N ' = V~' from ( 2 ) 



N' = A-, ..... (N') 



