12 AEROPLANE PERFORMANCE CALCULATIONS 



The procedure is therefore as follows : 



First, note the resistances of the various items in the total 

 body resistance,* and then the vertical distance of the line of 

 action of each item from some convenient datum (such as the top 

 longeron of the fuselage), using positive signs for items which 

 are above and negative signs for items which are below the 

 datum. 



Then multiply each item of resistance by its appropriate 

 vertical distance and form the algebraic sum of the resulting 

 quantities. 



Finally, divide this sum by the sum of the items of resistance 

 (i.e. by R) and the result is the vertical distance of the required 

 line of action above the chosen datum. 



* For this calculation there is no need to deal with R t and R. 2 separately : it is 

 near enough to treat all the items on the same basis. 



