238 TAKING OFF OF AKROI'I.AXFS. 



II. — Lex(;tji of Run on (jrvOrNi) liKi'oKK Takinc; Off. 



Perliups the most striking- change which a pih)t used 

 to European conditions will notice in flying- here is the 

 g-reater run required to take oft'. Especially is Ihis the casei 

 when the machine is heavily loaded and the air is hot. 

 Lieut. -Colonel 8ir H. A. van Kyneveld refers repeatedly in 

 his technical report* to the ditticulty of taking oft' his 

 heavily-loaded machine : — 



" . . . . had to cut down more trees, Shirati, to 

 take off." 



" Abercorn. — Only possible and safe take oft' here is 

 before sunrise, down slope, whatever wind." 



" Unexpected difficulties taking' oft', due altitude and 

 comparatively high temperatuie and moist atmos- 

 phere." (At Living-stone.) 



" Every take oft' Northern Rhodesia was touch and go 

 for the first few minutes, tail skid scraping- trees." 



And so on. 



The following- theoretical considerations Avill enable us 

 to estimate the effect of altitude and temperature {i.e., lowness 

 of density) on the leng'th of run to take off'. The least 

 favourable case of no wind is taken. 



AVe can divide the run to take off' into two portions: — 



(1) A run with tail down until some speed— say 20 miles 

 per hour — is obtained. This distance, ^vliich is quite vshort. 

 will be unaffected by the density of the air. The speed is 

 too slow for the air resistance to play an imi^ortant part. 



(2) A run with tail up, in Avhich the speed rises from 

 20 miles per hour to the flying' speed. This is by far the 

 more important and greater jjortion of the run. We Avill 

 assume that the jiilot takes oft' at the minimum flying- speed, 

 and that we may negdect the frictional forces connected Avith 

 the contact with the ground. In this Avay we shall g-et an 

 underestimate of the leng-th of the run lequired, for he will 

 probably not lift the machine from the ground until he lia.-^ 

 some slight reserve of speed over the minimum flying- speed. 



J^ot .s- =the distance of the run from the place where the 

 speed is 20 miles per hour. 



7^ = the horse poAver of the engine. 

 1] = propeller efficiency, 

 r = speed in feet per second. 

 ?n = mass of the machine in pounds. 

 c/ =32-2 feet per second per second. 

 Then, thiiist — resistance = mass x acceleration. 



* " The Aeroplane," a'oI. xviii, 13, p. 670. 



