496 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1940 



may well become unpopular where the highest aerodynamic efficiency 

 is sought), 6 such pairs may be the practicable limit. This would 

 give us 12 engines, which, at 3,000 horsepower apiece, makes the 

 total power 36,000. At 15 pounds carried per horsepower available 

 this would give a total flying weight of 540,000 pounds or some 250 

 tons. Such a craft would naturally be a large boat, taking 200 

 passengers or more; and that is the largest flying craft that can be 

 said to be now in sight, although I ought perhaps to mention that 

 in a lecture to the students of the Royal Aeronautical Society, who 

 alone perhaps might be expected to live to see it. Dr. Roxbee-Cox was 

 bold enough to include an American forecast for a boat of 3,120 

 tons. But difficult as it may be to foretell accurately the future 

 of the large flying boat, there can be little doubt that we shall soon 

 see such craft in active competition with their older rivals — which 

 use the surface of the sea — for all rapid passenger transport on the 

 important Atlantic routes. 



The future of wing loading is hard to forecast. As has been 

 mentioned, the early Wright airplane was loaded to 1^^ pounds per 

 square foot. By the time of the Great War this had risen to the 

 neighborhood of 10 pounds, but even Hallam ("Pyx"), writing 

 a few years later of his vision of a 200-ton flying boat, did not put 

 it above 8 ! In the succeeding years, however, the figure has grown 

 gradually until it is now in the neighborhood of 30; and while 

 loadings of 40 to 50 are talked about for future craft. Sir Allen 

 Cobham has suggested that, provided the bulk of the fuel is added 

 by refueling in the air from a tanker, loadings as high as 60 or even 

 70 should not be unattainable. The real limiting factor here is the 

 take-off and the landing. With landplanes, the disadvantage of 

 high loadings is that they lead to great increase in the size and 

 cost of airdromes, unless this can be avoided by the use of an auxiliary 

 like the Mayo Scheme or by some form of catapulting, or by the 

 use of the "tricycle" undercarriage, now so rapidly coming into 

 use. This consequence of high loadings does not apply in the same 

 degree to the flying boat, but even there it has the disadvantage of 

 requiring the use of natural harbors of large size with not too much 

 local water traffic. 



Can one, however, relate these speed ranges of 500 to 600 for 

 military craft, and 200 to 300 for civil, with wing loading, with 

 or without refueling in the air? We have the relationship that the 

 minimum air speed of flight is measured by the square root of the 

 wing loading. If we assume the use of such aids as wing flaps, 

 we can calculate for sea-level conditions just what the stalling speed 

 for any given wing loading must be. 



