102 AEROPLANE PERFORMANCE CALCULATIONS 



Propeller Performance Curves in Standard Density Air. 



Reference must now be made to the curves on pages 100 

 and 101 : these are founded on Bolas' curves for the output of 

 well-designed propellers : they give rj r and rj R plotted on a base 



of J for a series of values of , these values being marked on 



* o 

 the curves. 



The next thing to do is to draw up a table on the following 

 lines : 



V has been decided on, d has been found and n Q is known, 

 therefore J can be found from the formula 



J = V 

 V" 



The second and third columns in the table can now be filled 

 in by reading rj T and rj R from the appropriate curves at the value 

 of J determined. 



V and H being known, the last three columns can be filled 

 up,* remembering that 



P T = H77 T and P R = H^. 



The last three columns contain the necessary data for plotting 

 P T and P R on a base of V, i.e. the propeller performance curves 

 in standard density air. It is advisable not to plot these curves, 

 however, at the present stage, but to plot them later on over the 

 machine performance curve in standard density air. 



Propeller Performance Curves at an Altitude. First, 

 draw up a table in the following form, allowing for six horizontal 

 lines of figures : 



* It will always occur at rr- = i'o that TJT = T?R and P T = PR. 



