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Aviation History
1925
1925 - 0594.PDF
will also, it is hoped, be usedjby Capt. Wilkins in his projected expedition to the Antarctic, as related elsewhere intEts "issue ol FLIGHT. Tn "France also Seveidi mauhims have been built with this engine arrangement, notably the C.A.M.S. and Latham flying boats, both of which types have proved very successful. Wind tunnel experiments carried out in this country on tandem arrangements also seem to indicate that fundamentally there is no reason to expect it to give trouble, provided the rear airscrew is designed with slightly larger pitch than that of the tractor, so as to allow for the fact that it is working in the slipstream of the front propeller. One advantage of the tandem arrangement is that, the centres of thrust of the two engines being concentric, no turning moment is set up by the fact of one engine stopping, as is the case when the engines are arranged on the wings. It is gener- ally thought that when the front en- gine stops and the rear airscrew is no longer working in the slipstream of the front screw, the pitch of the pusher, having been made purposely greater to allow of its normal working in the slip stream of the front screw, is too great, and that thus a certain amount of loss of efficiency is incurred. Practical tests have not, how- ever, so far as we are aware, proved this to be a serious objection, and we believe that in the Bolton and Paul " Bodmin," for in- stance (which has its engines centrally placed in the fuse- lage with transmis- sion drive to air- screws on the wings), it was found that with the front engine and its pro- pellers stopped, there was no appre- ciable loss of efficiency when the rear engine with its two "over-pitched" pusher screws was running by itself. It would thus seem that possibly this arrangement of er- gines is deserving oi more attention than it has hitherto received in this country. From a practical point of view, there is certainly consider- ably greater opportunity of effecting repairs or adjustments to an engine centrally placed than to one placed out on the wing, and the performances of the Caproni and other machines in which the tandem arrangement is employed seem to show that, from the point of view of efficiency also the tandem arrangement may have its advantages. Certain problems may crop up in connection with the presence and absence of slipstream on the tail planes, but in this respect the twin engine arrangement should if anything be preferable to the use of a single engine on a flying boat in which, when the engine stops, the whole of the slipstream disappears, whereas with the tandem arrangement there should be, if anything less difference in trim between " engine off " and " engine on " conditions, as only the slipstream of one engine would disappear in the case of accidental stopping of one engine. In the main, the photographs of the Caproni 80 are self- explanatory. The central hull or fuselage is, as already THE CAPRONI 80 '' Jupiter '' engines. SEPTEMBER 17, 1925 mentioned, a boat-built structure, and the only unusual feature of the machine is the use of a short top plane. The front view of the machine gives an excellent idea of the angle at which the interplane struts slope inwards. Presumably this arrangement has been chosen in order to reduce the end loads on the top spars. We have no infor- mation relating to the wing section used, but the photographs show it to be a fairly thick section, which fact, doubtless, accounts for the use of single-bay bracing. The two-wheeled undercarriage is attached underneath the inner interplane struts giving a wide wheel-track, and the whole arrangement seems to indicate the possibility of turning the machine, by suitable shaping of the hull, into a twin- engined amphibian flying boat. This, however, is not, we believe, the inten- tion, but the par- ticular arrangement chosen is due chiefly to the tandem en- gines and to a desire to provide an un- restricted field of fire for the two gunners. It is stated, how- ever, that should the machine be forced to descend on the water, the boat -built hull would keep it afloat for an indefinite period, while special air bags mounted under the lower plane, woi.ld give the necessary lateral stability on the water. The two Bristol "Jupiter" engines are mounted on a structure indepen- dent of the wing structure, in the forii of two sets of struts forming the letter " M " as seen in side elevation. The accessibility of the two engine units is well brought out in the photo- graphs, and it may be added that the petrol tanks, which are placed between the engines, are separated from them by fire-proof bulkheads. Per- haps, according to British ideas, a preferable arrange- ment would have been to place the tanks in or on the top plane, giving direct gravity feed to the engines, but doubtless Signor Caproni was induced to place them between the engines by his desire to concentrate all heavy weights as far as possible so as to maintain good manoeuvrability. The pilot's cockpit is placed in line with the leading edge of the lower plane, below and slightly aft of the front engine. In view of the proximity of the tips of the front propeller, the substantial wind-screen fitted does not appear to be an unnecessary precaution. Of the two cockpits for the gunners, one is arranged in the extreme nose, where the field of fire forward, and, in fact, throughout the whole hemisphere, is particularly unrestricted, while the rear gunner is situated just aft of the wing, where he commands a view and a more or less unrestricted field of fire in all directions, except forward, downward, and to some extent aft, where his field of fire is to some extent blanketed by the biplane tail. Altogether the machine seems well designed for self-protection against attackers. Its main : View showing mounting of the two Bristol The petrol tanks are placed between the engines. 594
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