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Aviation History
1913
1913 - 0098.PDF
IA IGHT JANUARY 25, 1913. HYDRO-AEROPLANES-II. By V. E. JOHNSON, M.A. The Floats. NATURALLY in designing their floats, some took as their model the hull of a fast racing motor boat, evidently because here they saw a partial solution of the problem. The design taken was that of the hydroplane or gliding boat. In these boats the faster the speed the less the extent of boat surface in contact with the water— thereby reducing the extent of wetted surface to a minimum and so lessening the resistance. In Fig. 6 we have a cigar-shaped body i.e., a hull to which are fitted on either side a number of inclined surfaces like a Venetian blind. When a boat of this character is driven through the water by a propeller not in the water but in the air, the tendency is for the weight, which is first of all supported by the boat-like hull, to become gradually supported by the inclined planes or slats. The boat thereby tends to rise out of the water. The greater the speed obviously the less the number of inclined surfaces required, and the number of immersed planes will thus become less and less—the resistance thereby diminishing proportionately—until finally we have the machine skimming over the surface of the water supported, it may be, solely on the four lowest inclined planes. It should also be noted that the slats as well as being very efficient hydroplanes are also very efficient aeroplane surfaces, as was first shown by Philips. The machine is thus supported partly by water and partly by air. In a machine of this description, the propeller must either be an aerial one or one fitted on an inclined shaft, or else when the hull rose out of the water, the propeller would rise with it and thereby lose all its efficiency owing to the great differences in the two types. |This design was the original one tried by Fabre, but given up by him on account of the planes picking up weeds and other floating debris. The same idea has quite recently been revived by Messrs. Short Bros. (Patent 22407), see Fig. 7. It will be seen that there is a set of twin circular section floats of streamline form as floats, and a series of horizontal cambered slats or vanes (termed hvdrovanes) which are used for hydroplaning purposes. Each set of hydroplanes is so attached to the chassis as to be capable of being drawn up out of the way when alighting on land. The tail of the machine is also fitted with a series of hydrovanes, 1). They are attached to a tube controlled by the pilot—this tube jerking up the nose of the machine, would be to cause it finally to probably pancake badly, with serious damage to the floats and possibly the whole machine. A great deal would undoubtedly depend on the smartness of the pilot. It scarcely seems possible that the water-catching tube would act quickly enough unless it were of some size, and in that case it would appear that the water resistance to the pipe, J, through the water, might more than compensate for the extra weight deposited in B. Owing to the drawbacks to the hydrovane type of float already stated, Fabre invented the well-known type of float which now bears his name, i.e., a flat-bottomed float with a curved upper surface (see Fig. 8 (i)) set at rather a large angle of incidence. Their plan form is usually approximately square—or with a length slightly in excess of their breadth. They permit, when the flotation is ample or the machine well surfaced, i.e., lightly loaded, a rapid get off, and they also act in the air as lifting surfaces—their some what large angle of incidence, however, must give rise to considerable drift and therefore proportionate resistance. In theory they have been considered to show no tendency to dive—this is only correct, however, so long as the leading edge does not dip under the water, should it do so, a dive must be the inevitable result. Being a short flat-bottomed float (fore and aft), they are more or less subject to violent shocks when alighting, which has to be minimised by more »c Flgr. 6.—(a) Forlaninl-Del-Fabro's hydroplane, (b) Craccoand Rlcaldoni's hydroplane. Fig. 7.—Messrs. Short Bros.' system—combined hydrovanes and floats. communicates with a tank, B. A float, C, is arranged to support the machine when on the water. It will be noticed the principal hydrovanes are carried well forward—but in all machines of the tractor type in which the weight is well forward—there is a tendency more or less when alighting—especially if the water ba rough and the prow of the float strikes a wave, for the whole machine to turn a somersault—a sudden application of the brake on the front wheel of a bicycle has exactly the same effect. The hydrovanes, D, are set in such 5. manner that as soon as the machine touches the water (tail horizontal) these vanes begin to exert a depressing effect—but as this depression is increased, their negative angle of incidence is so altered until it either becomes zero—or even positive and so causes the tail once again to lift. This effect can, if necessary, be still further augmented by depressing the front part of the tube A, so that water is forced up into the tank B and so as-ists in weighing down the tail. The support of the vanes, A, it will be noticed is also tubular, and can be used for the same purpose. The depressing of the tail in this manner and consequent checking of the speed of the machine, as well as the tendency it would undoubtedly have under certain conditions of or less flexible connections. This type of float is placed one in front and two behind (Voisin Canard), or two in front and one behind (original Caudron). Reference has already been made to floats of the catamaran type ; these are generally arranged in pairs, are usually rectangular in shape with curved bows and sterns, generally their bows are more or less turned up and pointed, but some are merely rounded off. The former is undoubtedly the better plan, especially when for use on rough water owing to their cutting through the waves the more easily. In flight the head resistance of this type of float is small and they also get off the water under favourable conditions fairly quickly. Being in apteroid (end on) aspect they are not so efficient as the Fabre type, either as hydroplanes or aeroplane surfaces. The speed at which " skimming" over the surface of the water commences, increases with the length of the float, but before skimming can commence, it is necessary that the machine travels over the surface of the water at a certain high velocity, and it is easier to drive through the water a vessel, or hull, end on, than broadside. As a matter of fact with the same relative power of say i-h.p. to 20 kilogs., a vessel 12 metres long is more rapid 98
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