128 AEROPLANE PERFORMANCE CALCULATIONS 



of curves from the data of the tables of pages 130 and 131 

 (plotting y upwards and x to the left] on any scale he likes, and 

 then trace them on to celluloid as described above. Such a large 

 sheet can be used on small-plotted performance curves too, of 

 course. 



The points in the tables which are printed in heavy type fall 

 outside the general area of plotting, but will be useful in fixing 

 the last part of the curves to which they refer. 



Consumption and Revolutions when Throttled. At any 

 altitude desired take the plotting of P', P T ', and P R ' on V and lay 

 the celluloid throttling curves over it with speed axis on speed 

 axis and horse-power axis on horse-power axis. 



Between the minimum speed and the top speed a certain 

 number of the throttling curves will cut the P' curve : note the 

 values of the speeds where the intersections take place and. call 

 them V/, V 2 ', V 3 ', etc. Note also V T1 ', V T2 ', etc., and V R1 ', V R2 ', 

 etc., the speeds at the points where the same throttling curves 

 cut the P T ' curve and the P R ' curve. 



Then construct a table in the following form, allowing for as 

 many horizontal lines of figures as there are intersections on the 

 P' curve : 



V. 



"X^r') 2 ' i 



Next fill up the first three columns with the values V/, V 2 ', 

 etc., V T1 ', V^', etc., and V R1 ', V R ./, etc., just determined. 



Then work out the other columns. 



cr can be found for the altitude in question from the curve on 

 page 104. 



/= -1 6 1 for stationary and '262 for rotary engines. 



Then a is the ratio of the consumption per hour to the full 

 consumption in standard density air and ft is the ratio of the 

 revolutions to the standard full revolutions. 



The same method can, of course, be used for standard density 

 air. 



