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Aviation History
1932
1932 - 0709.PDF
o^r a \ c FLIGHT, JULY 15, 1932 L>' The A.W. XV Monoplane (Continued from p. 623.) AST week considerations of space prevented us from referring to the structural features of the A.W. XV monoplanes designed and built by Sir W. G. Armstrong-Whitworth Aircraft, Ltd., for Imperial Airways, Ltd., for the African sections of the London-Cape Town air route. The main features of what may be termed the aerodynamic design were dealt with, but as certain data relating to the machine have now become available, an examination of these may be of interest before we take up the structural side. The table of data shows that the certificate of airworthi ness covers a gross weight up to 20,000 lb. As the tare weight, i.e., weight of the machine completely equipped, with cabin furnishings, etc., but without load, crew, fuel or oil, is 13,940 lb-, we obtain a ratio of gross weight to tare weight of 1.435. Put in a different way, the machine carries as disposable load 43.5 per cent, of its own Weight. Comparisons of machines on this basis are always apt to be a little doubtful, since the definition of tare weight is somewhat vague. In this case, however, the tare weight includes everything ; in other words, the weight of the machine in full flying trim, but without any of its disposable load. The ratio of 1.435 may appear slightly low, but it should be remembered that, for one thing, the machine is a cantilever monoplane, and also that it is designed to have a rather large power reserve, which ir» merely another way of saying that it carries a consider able surplus of engine weight as well as engine power. Taking these considerations into account, and remember ing also that the machine is quite a large one, the ratio of gross to tare weight is by no means bad, the more so as clean aerodynamic design rather than very low structure weight has been the aim of the designers. When petrol for a range of 400 miles is carried, the pay load is 4,350 lb., which corresponds to 3.2 lb./h.p., ARMSTRONG-WHITWORTH A.W. X\ ..-. MONOPLANE 4 " Double Mongoose Dimensions Length o.a. Wing span Overall height A reas Main plane (total) Ailerons Tail plane Elevator Rudder "C,3^^ • t«M Weights Tare". ty«* Petrol and oil Pay load Max. permissible gross wt. Range " Engines ft. in. . 71 6 . 90 0 . 14 0 sq. ft. . 1,285 131-7 154 58 22-2 60 lb. 13,940 1,600 4,350 • 2P.000 m. 21,80 27,45 4,26 m.2 119,5 12,2 14,3 5,4 2,1 5,6 kg-6 340 729 1 978 9 100 THE " ATALANTA " IN FLIGHT : This view from above gives a good idea of the plan form, and also shows the neat merging of the engine housings into the wing surface. (FLIGHT Photo.) 661 400 miles (640 km.). If pay load is reduced to 3,500 lb. (1 590 kg.) the range can be increased to 600 miles (965 km.) Performance At present no performance figures are available, as the first machine has been but recently finished based on normal power. Again, one should remember that a large power reserve has been a fundamental design feature, so that the pay load per horse-power actually used at cruising speed is probably very much greater. At full gross weight, the wing loading is 15.5 lb./sq. ft., and the power loading 14.7 lb./h.p. We gather that in the form in which the A.W. XV is to be used in Africa it will not be loaded up to the full gross weight permitted by the C. of A., but will gener ally weigh some 18,000 lb. laden. This will bring the wing loading down to 14 lb./sq. ft., and the power loading (normal) to 13.25 lb./h.p. The minimum speed will probably be in the neighbour hood of 60 m.p.h. Actual performance figures are not yet available, but it is thought that the cruising speed will be 120 m.p.h. or a little more. A rough estimate which we have made indicates that the maximum speed (which is not, of course, a criterion of a machine's usefulness as a commercial pro position) should, for such a clean design be rather more than 140 m.p.h. The actual figure will be available when the first machine has passed its tests at Martlesham. Structural Design Interesting as is the A.W. XV from an aerodynamic point of view, it is no less so when one has the opportunity, as we had recently, of examining the in ternal structure. Apart from the general system of construction adopted, one is particularly im pressed by the amount of thought which has obviously been given to the subject during the planning stages. Too frequently one sees an aircraft in which one feels that the general primary structure was decided upon without a great deal
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