MACHINE PERFORMANCE CURVE 25 



The above equations having been solved tabularly, we have 

 values of V and P for values of X from 'I to I'O : these values of 

 V and P are the data required for plotting the performance curve 

 for standard density air under the assumptions of the Second 

 Method. 



Third Method. Assumptions. Line of flight horizontal. 

 Propeller thrust horizontal at all speeds of flight and passing 

 through the centre of head resistance. 



Definitions. These are the same as in the Second Method, 

 but in addition 



R! and R 2 have the definitions given in Chapter I. 



S, as before, is the total wing area in square feet. 



S' is the area of wing affected by the slip stream. 



d is the propeller diameter in inches. 



(i + &)V is the total slip stream velocity in miles per hour. 



Seeing that after all the slip stream effect is only a correction, 

 it follows that corrections on it will not have much influence on 

 the main problem. It is therefore sufficiently accurate to take 

 the parts of the machine which fall inside the propeller circle in 

 front view as being subject to slip stream action, and the rest as 

 being clear of it. This applies also to the wings : the total 

 length of top and bottom leading edge falling within the propeller 

 disc in front view is first measured, and then S' is estimated as S 

 multiplied by this length and divided by the total length of top 

 and bottom leading edges for the whole machine. 



We now have, somewhat as before 



VT 



T = [(i + *)% + R 2 ] + . . ( 2 ) 



L = -00237^13 - S' + (i + ) 2 S'](i-467V) 2 . ( 3) 



W/ = L<7 - ck c ~) . . (4) 



,. = X/W . (5) 



Equation (6) is taken from equation (8), Chapter VI. of " The 

 Design of Screw Propellers for Aircraft," by H. C. Watts.* 

 From equation (4) we obtain, as in the Second Method 



* Published by Messrs. Longmans, Green & Co. 



