EVENING DISCOUKSES. 



385 



the usual inaxiuuun, but OiJ luis been exceeded by ^lessrs. Haudley Page and by 

 the Blackburn Company. 



The stalling speed, the miiiinuim speed at which tlie machine can flv, i.s 

 inversely proportional to the square root of the maximum lift coefficient,' and 

 since W = k^p-^i''-. W/s^h^pv-, this quotient expressing the 'loading,' i.e.. 

 the weight carried per unit wing area ; the loading varies between 5 lb. and 

 10 lb. per eq. ft. The drag or i-esistance to the motion of the wing is equal to 

 k„psv", the drag coefficient k„ also depending upon the shape of the wing 

 section and the angle of attack. As that angle increases, L\, decreases at first, 

 then increases more and more as the angle grows steeper. ' But kz is always 

 smaller than ki, and the force D required to move the wing is given by 

 D = W k^/k^. The resistance of the rest of the machine is about the same in 

 amount "as that of the wing. The resistance is entirely due to the friction 



Fici.2. POSSIBLE LOADING OF WINGS £ BOOT 

 ^ OFHIGH SPEED AEROPLANE IN FUGMT. 



ssecs. 



tr.103 a-io>, j^.j, 



LoaudLurvTaiL- TJbe^nft. 



Anale cf Incidence of Winas-O'. ForwatrcLSpeedUWrniles/hT: 



B.E.2 MACHINe WITH ISO HJ^ ENGINE. 

 Weight -ISSOVk 



BxnsOmceuvrwrmal flying ajtiliule-340lie at 100 fs. 

 Mcut speed, forhartzontoLfUglit -SSmj.p.iv. 

 rt> j^ CotUtoI leverages as- uvB.B. 2c. 



ise afiffrlhi^ 



3*5 



Seconds. 



Ipv r loffp. 



between the moving body and the air, and to the viscosity of the air, the 

 friction itself is due rather to the eddies, which owe their origin to the viscosity, 

 than to the direct motion of the machine through the air. 



As regards the engines, the weight per horse-power is smaller for radial 

 air-cooled engines than for water-cooled motors ; 3 lb. per horse-power is perhaps 

 a reasonable figure. According to Bairstow, a light aeroplane capable of 

 travelling at 125 miles p.h. would be able to carry a useful load of 270 lb. out 

 of a total weight (machine, engine, and pilot) of 2,100 lb. The modern Bristol 

 Pullman triplane for fourteen passengers, capable of a best speed of 130 m.p.h., 

 weighs empty 11,000 lb., and fully loaded 18,000 lb., 4,375 lb. of that total 

 being available for cargo or passengers. The engines are not yet reliable in the 

 sense that marine engines are reliable. The useful load can be increased by 

 making the structure light. A light ma'hine can be fiown at a lower angle of 

 attack, but tlie structure must remain sufficiently strong, and the calculation of 

 the stresses is not an easy matter, except when the machine is moving horizon- 

 tally. In steep diving, at twice normal speed, the stresses might rise to sixteen 

 times their magnitude for normal flight, if the pilot were able to change his con- 

 trols instantaneously, and although that is impossible, the controls can be changed 

 within one-fifth of a second. Foi' these calculations the ' load factor ' is 

 1920 c o 



