120 AEROPLANE PERFORMANCE CALCULATIONS 



Next fill up the first three columns by copying from the 

 immediately previous work. Then work out the columns in 

 succession. 



The table should, of course, be extended beyond the limits 

 here shown, by adding three additional columns for each of the 

 values VK z> 3 , etc., of v. 



Now plot tan <f> lt tan < 2 , etc., all on V as a base, and note 

 the minimum value of each curve : these minimum values are the 

 tangents of the best gliding angles relative to the ground in 

 standard density air against head winds of strength v lt z; 2f etc. 

 Let these values be called tan 4^, tan 3> 2 , etc. Also note the 

 values of V at which they occur, and call them V 1} V 2 , etc. 



Now draw up another table in the following form, allowing 

 for as many horizontal rows of figures as there are values of v 

 included in v lt z/ 2 , etc. : 



v. 



tan *. 



Next fill up the v column with the values v it z/ 2 , etc., the 

 tan <3> column with the values tan <J> lf tan 4> 2 , etc., just deter- 

 mined, and the V column with the values Vi, V 2 , etc., just de- 

 termined. 



Now from the altitude at which the values of v are required, 

 find a from the curve of page 104, and then fill in the v 

 column, using the relation 



> n 



V = 



The table can be extended to the right to include any number 

 of altitudes desired. 



Thus we have, at any altitude desired, a column of v against 

 which the V and tan <& columns can be plotted, giving the Air 

 Speed Indicator Reading for best gliding angle relative to the 

 ground, and the tangent of the best gliding angle relative to the 

 ground, all plotted against the velocity of the head wind. 



These curves, of course, include such information as is given 

 by the immediately preceding piece of work, but in a slightly 

 less approximate form. 



