46 AEROPLANE PERFORMANCE CALCULATIONS 



we have that the added lift Z, due to introducing the full power 

 slip stream, is given by 



L = -oo5i r S'.,V 2 -5 



io 5 T 



d ' 



Hence L is known for the assumed value of X. 



This additional lift is equivalent to an equal reduction of W 

 and therefore, assuming as we do the value of X to be unaltered, 

 the machine, instead of flying at X V at this value of X will rea"lly 

 fly at a speed 2 V given by the equation 



v . w /W - L 



2 " "" 1 



W 



Again, the total resistance under slip stream conditions is 



R, + R 



(compare, for instance, page 26), whereas under conditions of 

 no slip stream it is 



Therefore, the added resistance R due to introducing the full 

 power slip stream is given by 



R = ^ y2 + JL 



lo* L/D 



10 TR, L 

 = 1-39' ^ L/D 



^ 

 L/D 



But this is on the assumption that the speed L V is maintained, 

 whereas, as we have seen, this speed is actually reduced to 2 V. 

 Therefore the horse-power required by the machine is really 

 altered to 



R i^ ; 



