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Aviation History
1926
1926 - 0382.PDF
JUNE 10, 1926 of forced landings become greater, thus failing to give the full advantage which the three-engined arrange- ment should theoretically offer. Lest we should be misunderstood, and be accused of " damning the three-engined aeroplane with faint praise," we would emphasise the point that at the moment we share the hopes of those who believe that this type of machine will be found to add greatly to the safety of flying. At the same time, it is no use shutting one's eyes to the fact that so far the type must be regarded as being in the experimental stage, and that it is likely it will require considerable development before giving full value. It would be futile to assume that a machine, just because it is a three-engined machine, is necessarily the three-engined machine. One might as well claim that a tractor aeroplane, because it is a tractor, is the last word in tractor aeroplanes. Doubtless in years to come we shall see a variety of three-engined aeroplanes, unless the experience gained with the early ones should prove so disappointing that the type is abandoned, a contingency not, we think, at all likely to come to pass. The great thing, for the moment, is that a real start should be made, and the possibilities of the three-engined aeroplane be thoroughly explored. It is for this reason that we look forward with more than ordinary interest to the completion and flying tests of the new de Havilland machine now under con- struction, and an illustrated description of which appears in this week's issue of FLIGHT. The de Havilland Aircraft Company has had more experience of commercial aircraft design and construction than any other British firm, and, although in the case of the D.H.66 the firm has not had altogether a free hand, having had to a considerable extent to comply with the requirements of Imperial Airways, Ltd., the new machine incorporates a good deal that is purely " de Havilland." In this connection it is of interest to compare the D.H.66 with the Handley Page W.9, " Hampstead." The total loaded weight of the former is 14,700 lbs. and of the latter 14,500 lbs., so that the two machines are sufficiently nearly identical as regards weight. The wing areas are also approximately identical, so that the wing loadings are about the same. The D.H.66 is to be fitted with Bristol " Jupiters," while the " Hampstead " has three Armstrong-Siddeley " Jaguars." At the moment we are not quite clear which type of " Jupiter " is to be employed in the de Havilland machine, but it would seem likely that the D.H.66 will have rather greater power than the " Hampstead," and consequently a somewhat smaller power loading. At any rate, the two machines promise to be nearly enough similar to allow of a direct comparison, and it will be interesting to see how two famous designing firms solve the same problem. One important difference is to be noted, however, whereas in the " Hampstead " the weight of petrol carried is but 1,700 lbs., in the D.H.66 provision has had to be made for carrying no less than 300 galls., or roughly 2,100 lbs., the machine being required for covering longer stages. A result of this is that the paying load is decreased correspondingly, the figures for the two machines being 2,260 lbs. and 3,220 lbs. respectively. It will be seen that this difference is not entirely accounted for by the difference in the amount of fuel carried, but is made up also by a difference of approximately 500 lbs, in the empty weights, the " Hampstead " being the lighter of the two. Whether or not this difference is due to the steel structure of the D.H.66 fuselage is difficult to say without knowing the item weights of the two machines, information which we do not possess, but it would appear probable that to some extent at any rate this may be the explanation. It should be realised that with the steel tube structure it is necessary to make separate " boxes " for cabin, luggage compartment, etc., which must add a certain amount of extra weight. Incidentally, we believe that the De Havilland firm would have preferred to use, in the D.H.66, their usual plywood-covered fuselage, but that the steel tube structure was more or less demanded. At any rate the two types of machines are so nearly alike that direct comparisons in the future should prove interesting. There is yet another three-engined machine coming along, designed and built by Sir W. G. Armstrong Whitworth Aircraft, Ltd., which, like the D.H.66 and the " Hampstead," is a biplane of very similar general arrangement. It will thus be seen that in the near future there should be no lack of practical experience of three-engined aircraft, and if the present policy is vigorously pursued, Great Britain should be able to take a leading position in the production of this type. It is, perhaps, a somewhat significant fact that all three machines should be of the biplane type, since the monoplane seems to be more favoured abroad, famous examples being the Fokker monoplane on which Commander Byrd flew to the North Pole and back, and the Junkers, which is used extensively on the German air lines. Both of these are cantilever monoplanes, the Fokker being of the " high-wing " type and the Junkers of the " low-wing " type. From the point of view of wing weight there is probably little to choose between the two, although superficially at any rate it would seem that the " low-wing " type would lend itself rather better to " burying " the engines in the wing, and thus save a certain amount of resistance. The next few years will probably see quite a fight between the biplane and the monoplane in this class, and we should hesitate to express an opinion as to which type is likely to survive. While on the subject of three-engined aeroplanes we should like to refer to a matter raised at one of the Royal Aero Club House Dinners by Major F. A. de V. Robertson. He suggested that for use in the Dominions, especially in Australia, British designers might be well advised to study the possibilities of the small three-engined aeroplane. He even suggested a machine with three Bristol " Cherubs," a remark which caused some little amusement. Actually the suggestion is by no means as ridiculous as might appear, since a machine with a total of 100 h.p. could presumably carry some 250 to 300 lbs. of paying load, which would represent quite a respectable mail bag in certain districts of Australia. In any case, the small three-engined aeroplane should not be overlooked, even if one does not care to go as low as 100 h.p. A machine with a total of some 350 h.p. would probably be viewed favourably in Australia, and for this reason we are sorry that the machine with three Bristol " Lucifers," which was once said to be coming along, has not yet materialised. 328
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