FUTURE OF FLYING WIMPERIS 491 



without any increase of engine power, was first clearly pointed out, 

 little more than 10 years ago, by Prof. B. M. Jones, of Cambridge. 

 This required that all excrescences should be removed, and of these 

 some of the worst were the interplane struts and wires. When that had 

 been achieved, it was realized that much of the equipment hitherto 

 carried externally, especially in military types, must be put inside, and 

 with that attained, after a severe struggle, there arrived the modem 

 streamline airplane with its undercarriage, and even its tail wheel, 

 retractable into the body of the structure. What yet remained was 

 attention to those external surfaces scrubbed by the passing air stream. 

 Here guidance was given, curiously enough, by the experience of sail- 

 plane pilots, who had long found that a much better gliding angle was 

 attainable when the surfaces were not merely made smooth, but were 

 carefully polished, and even dusted before flight ! At the time these 

 minutiae of housemaid's care seemed fantastic, but experience, both 

 within wind tunnels and without, showed that the sailplane pilots 

 were right and that protuberances on a wing no more than a thou- 

 sandth part of an inch high produced a measurable drag. 



FLYING TODAY 



The consequence of these and other changes in design from the 

 original Wright machine brought a steady growth in speed, which 

 during the last score of years has increased by an average of well over 

 10 miles an hour in each year. 



This over-all increase in airplane performance is indeed impressive : 

 in speed from the 31 miles per hour of the Wrights to the 469 claimed 

 today ! Behind the change in external characteristics there have been 

 internal changes of an equally important character, such as the in- 

 crease from the Wrights' wing loading of ly^ pounds per square foot 

 to the figures of today when 20 to 30 and 40, and even more, are com- 

 mon. There has also been an equally impressive change from the 

 modest engine power of the Wrights to the four-figure powers of 

 modern practice. 



As far as growth in altitude and range of flight are concerned, 

 further progress must depend chiefly on improvements in the present- 

 day materials of construction, or in the discovery of entirely new 

 ones. At the moment dural is found best, not because it has any 

 higher ratio of strength to density than alternative materials, for in 

 that respect it differs little from steel, or even from cotton or rein- 

 forced plastic ; but because in comparison with steel its lower density 

 (little more than a third) enables thicker and therefore stiffer and 

 more fool-proof sections to be used. But, as in the case of steel con- 

 struction, the sections have to be fastened together with innumerable 

 rivets (more than a million in one "Golden Hind"), and this time- 



