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Aviation History
1932
1932 - 1298.PDF
maximum speed. The top speed of the de Havilland Dragon " is about 130 m.p.h. (official figures are not available, but flying the " Dragon " against a " Puss Moth," the former was the faster), and the " High-speed Figure " works out at 21.6, which must be regarded as very good for a twin-engined machine, and points to a low minimum drag coefficient. At 85 per cent, of top speed the cruising speed is 111 m.p.h., so that the machine is not by any means a, slow one. Thus both in structural and in aerodynamic efficiency the " Dragon " can be said to be well above the average. These two " figures of merit " are chiefly of interest to the technician, and may not convey very much to the potential operator, although the fact that the machine carries as disposable load such a large percentage of its own tare weight does tell him that his pay load is likely to be a very useful one. What the operator really wants to know is how much the machine will cost him, either per passenger seat or per lb. of pay load, and what the run ning and operating costs are likely to be. These figures are not quite as readily assessed as are the two technical " figures of merit " referred to above. But a very fair idea can be formed without going into a lot of perplexing figures. Some, years ago, at the lecture by Herr Martin Wronsky to the Royal Aeronautical Society, we believe, Mr. C. C. Walker, chief engineer of the de Havilland Aircraft Com pany, expressed the view that a transport aeroplane may be considered efficient if its first cost is less than £500 per passenger seat installed, and if, also, it carries a passenger 100 miles in one hour at the expenditure of about 2 gallons of petrol. Let us see how the new de Havilland " Dragon " fares when measured with Mr. Walker's yard stick. Normally the " Dragon " will have seating accommoda tion for six passengers. This number can be increased if a shorter range is sufficient. With six passengers (each assumed at 160 lb. weight, and allowing 45 lb. of luggage for each passenger), the cruising range is in the neighbour hood of 460 miles. The " Dragon " will be marketed at £2,795, so that the first cost per passenger seat amounts, on this basis, to £465.8. So far the machine is well below that laid down by Mr. Walker some years ago. When the machine is used on short routes, so that the number of passenger seats can be increased to eight, the cost per seat reduces to £349.4, an even more economical figure. Another way of looking at it is to examine the first cost per lb. of pay load. This, obviously, must be related to 1214
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