PROPELLER PERFORMANCE CURVES 



103 



v. 



The first thing to do is to fill up the V and P T columns by 

 copying from the previous table. 



The altitude to which V, P T ', and P R ' refer must now be 

 noted. Probably the altitude will be one at which it is desired 

 to find the top speed of the machine in order to see whether the 

 design meets a particular specification, or perhaps the designer 

 wishes to investigate the performance at a series of altitudes in 

 which case additional sets of two columns with headings suitably 

 distinguished from one another will be required. However that 

 may be, the altitude is now considered as known. 



The altitude being known, a is found by reference to the 

 curve on page 104. 



o-j is a quantity defined by the equation 



<r - p 

 en = 



where/ = -262 and q = 738 for rotary engines, while/ = -161 

 and q = '839 for stationary engines. 



The last two columns of our table can now be filled up by 

 using the formulae 



V = VjaandP T '- 



The last two columns contain the data for plotting the pro- 

 peller performance curve for full throttle at an altitude, but again 

 it is preferable to delay the actual plotting until the machine 

 performance curve at the altitude is ready. 



It is to be noted, by the way, that the indicated torque at the 

 altitude is cr times that for standard density air. 



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

 horizontal lines of figures : 



