AIR PERFORMANCE 59 



tan A - tan B 



tan (A - B) = - r -^ 



i + tan A tan B 



if tan A - tan B 1 



A - B = ta " (I + tan A tan B}' 



Now let A = tan- 1 ^ . (A) 



and B = tan " 1 (l) ' ' ' ' (B) 



and 



/. from 



where the angle is in radians of course. 

 , tan' 1 



where the angle is in degrees. 



Again, from (i) V - V 'y- . (V) 



Hence, substituting in (2), we have 



And from (3) and (V) we have 



We now have, after the burning of fuel has reduced the total 

 weight of the machine from W to W, the revolutions and rate of 

 consumption given by equations (N') and (5). 



