28 



AEROPLANE PERFORMANCE CALCULATIONS 



Fourth Method. Assumptions. Line of flight horizontal. 

 Propeller thrust horizontal at all speeds of flight. 



Definitions. These are the same as in the Third Method, but 

 in addition 



h^ is the height in feet of the centre line of the propeller shaft 

 above the line of action of the body resistance. 



h^ is the height in feet of the centre line of the propeller shaft 

 above a point half way between the top and bottom leading 

 edges : this point can be taken as being on the line of action of 

 the wing resistance. 



w 



w is the air download on the tail plane in pounds. 

 D L is the body resistance in pounds. 

 D 2 is the wing resistance in pounds. 



We now have somewhat as before 



r.YI 



375 



= [(, + ^ Rl + R 2 ]Q ! 



L = -00237^ [S - S' + (i + ) 2 S'](i'467V) 2 



(0 



(2) 



(3) 



Now take moments about the point on the line of action of 

 the propeller thrust which is vertically above the centre of gravity 

 (see figure) and we get 



