204 AEROPLANE PERFORMANCE CALCULATIONS 



On plotting c - against V we get at standard, 2000, 



4000, 6000, 8000, and 10,000 feet minima of '0093, '0092, 

 00905, '0091, "00895, an d '0088. On plotting these minima 

 against altitude we do not get a minimum, as the value is still 

 getting smaller even at 10,000 feet. 



We have carried the investigation far enough, however, to 

 show that with a head wind of even 20 miles per hour it pays to 

 fly high. 



In the course of the above plottings we find that the best 

 cruising speeds at the respective altitudes are about 82, 86, 88, 

 90, 91, and 94 miles per hour respectively. The curves are not 

 reproduced as they are of no special interest. 



Cruising Range against a Twenty Mile Head Wind at 

 6000 Feet. We see from the above that it will pay us 'to use 

 V ' = 90 : then by interpolating on the 6000 foot table above 

 we get V T ' = 10 1 and V R ' = 997. 



Also W = 6000, W = 3600, / = -i 6 1 and we can take 

 A = 193, while at 6000 feet <r = -843. 



... = '93 * -682 x 9 o* _ 

 6000 x 997 x i oi 2 



5385 



and 



= 26-65. 



Therefore the cruising range in miles is 



x - v't = 2110 - 20 x 26-65 = J 577 miles. 



This figure, together with the other performance particulars 

 already plotted on page 193, are all that are required in an 

 ordinary case. Any other figures that may happen to be wanted 

 can be got as explained in the earlier chapters. 



