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Aviation History
1932
1932 - 1296.PDF
FLIGHT, DECEMBER 22, 1932 The De Havilland. " Dragon ;; 2 " Gipsy^Major " Engines UPERFICIALLY there is little to tell one that the new de Havilland D.H.84, or " Dragon " as the class has been named, is a very remarkable aircraft. In external appearance it is just a plain, well- proportioned twin-engined aeroplane with wings of un usually high aspect ratio (if one may still employ this old- fashioned term) and a simple well streamlined under carriage. For several years it has been our custom to use two '' figures of merit '' in describing aircraft: The ratio of gross weight to tare weight, and the Everling " High speed Figure '' ~—, which is the minimum drag coefficient divided into the propeller efficiency. The reason for using 2kD instead of kD is that the value thus obtained is then directly comparable with that of machines the character istics of which are expressed in metric units. The ratio of gross weight to tare weight is an index of the struc tural efficiency of the aircraft, and the Everling " High speed Figure " is a measure of the aerodynamic efficiency in that for the same propeller efficiencies machines witl the same " High-speed Figure " will have the same mini mum drag coefficients. In the case of the de Havilland " Dragon," both thes< " figures of merit " have an unusually high value. Fo- example, the tare weight of the machine, equipped t( carry six passengers, is 2,300 lb. (1 045 kg.) and the per missible gross weight is 4,200 lb. (1 910 kg.), so that th< ratio of gross to tare weight is no less than 1.825. Th machine, in other words, carries as normal disposable load and not as in any way an overload, 82.5 per cent, of it own weight! This is a quite remarkable achievement, an£ has only been equalled, to the best of our knowledge, bj the de Havilland " Fox Moth," in which the value ex ceeds 90 per cent. The structural efficiency should, to b< really convincing, be related to the speed of the aircraft since a very slow machine can more easily be given t large ratio of gross to tare weight than a fast machine This is where, to some extent, the " High-speed Figure comes in useful, in that its calculation is based upor THE DE HAVILLAND " DRAGON " : This photograph, and the view at the top of the page, gives a good idea of the appearance of the new machine. The identification number E.9 is a trade registration, and indicates that the machine is still experimental. Since these photographs were taken the " Dragon " has been undergoing official tests at Martlesham. (FLIGHT Photos.) 1212
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