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Aviation History
1913
1913 - 0503.PDF
MAY IO, 1913. [/ycHf] Edited by V The Recent Discussion on Hydro-Aeroplanes. Continued from p. 498.) MR. G. P. BRAGG-SMITH (continuing the discussion) said: I agree pretty much with what Mr. Johnson has said, but I do not agree with him in connection with his remarks about the necessary tendency to dive on alighting, provided one have the front float set well forward so as to have a tendency to throw the front of the machine up and allow it to alight on its main rear float. Again, it is desirable to have the front float set well forward for other reasons, viz., to counteract the tendency of the rear floats to plunge in preference to having too great an angle on the front ot the rear floats, it being undesirable to have an inverted camber on the top of the float owing to its depressing effect whilst in actual flight. This tendency to dive is, of course, owing to the high propeller thrust, and the further out your front float the greater the leverage to overcome it. The setting of this float at a somewhat high angle of incidence also assists you, but may cause a lifting effect tending to upset the machine ; for this reason I should suggest a cigar-shaped front float. With regard to dimensional relations, I strongly advocate a long float having an aspect ratio of even 12 or 15, which offers less resistance both in the water and in the air, and which also attains its flying speed quicker, due consideration being given to the simultaneous lifting action of the wings, the ease with which such a float can be driven through the water allowing such action to come into play and more than compensate for the hydroplaning effect of a float with a lower aspect ratio, such a system doing away with a large distribution of lateral resistance, which is always bad. I also advocate a step which should be situated under the centre of gravity, and a sweep down or dip at the rear end of the float, which I have found from actual experiment greatly assists the final leaving of the water, and the avoidance of any suction or drag effect. With respect to what I consider to be the most efficient type, it is one with a long central float, in which neither pilot, passenger, nor engine should be placed, owing to the lesser moment of inertia attained by such a system, it being of the greatest E. JOHNSON, M.A. TWO LEADING FLOATS _ L.NE OF THUWT Diagram A. importance, so far as stability is concerned, that the centres of gravity, of pressure, and of head resistance should be coincident, and the propulsive action of the propellers pass through the same point. There is also the question of the controls to be considered, to take, for instance, the Ridley and other machines, in which they are situated in the floats ; in the case of damage to the floats these might be straightaway put out of action. In the case of full-sized machines, all floats should be turtle backed so as not to ship any water. . Mr. F. Mayer criticised the last speaker's views with respect to very long floats, and pointed to the failure of early experimenters to quit the water with such. Possibly, if provided with a fin at the rear, which could be operated by the pilot, such could be jerked of! tne surface of the water—the great trouble being the travel of the centre of water-pressure, as more and more of the float came out of the water. Mr. Mayer also asked if anyone had tried the effect of using a small marine propeller (in addition to the aerial one) for launching purposes, in order to overcome the high centre of thrust, and, also, if anyone experimenting with power-driven plants had tried the effect of using the exhaust steam or gases on the under neath side of the float with a view to reducing the friction from water to air-air or rather to gas-gas. Mr. L. H. Slatter, speaking on the subject of flotational stability, said : From the commencement of my experiments on hydro aeroplanes I have endeavoured to obtain flotational stability by having a fairly large float track without introducing additional balancers under the plane tips. Then, owing to the faei thai my front floats—two in number—are the last to quit the water, i.e., my back one being totally out, the res-ult is that when the machine is struck by a side gust, instead of being blown over, the model is slewed round so as to face the wind and rises ; of course the very large base—19 ins. on a span of 3 ft. 3 ins.—prevents the model blowing over in a case like this. I also suggest as a remedy for l*ing blown over when stationary on the water, the fitting of thin aluminium keels. This would abo prevent damaging the floats in case of alighting on rough or stony ground. Further to obtain flotational stability, the machine should be low built, and that is one reason why I prefer a monoplane. Mr. A. F. Houlberg took exception to a remark of the writer with regard to the larger end of the float being towards the rear, and said : I am of the opinion that the greatest buoyancy should in- forward of the centre of the float, and also that you should have two floats in front and one behind in order to have a base to alight on. I also believe a streamline body fitted with vanes to be 1 In most efficient form ; it lifts better, and offers less resistance, if of true streamline form, and metal vanes, if properly constructed, can be made to partake of the nature of a perfect aerofoil. Mr. F. Whitworth said he thought that the position of the centre of gravity of the whole machine had more to do with alighting than the shape of the floats. Mr. A. F. Houlberg agreed that if 'the centre of gravity was sufficiently far back, the model would on alighting fall back on to its rear float. He also considered (in the case of floats having a larger rear end) that the machine would be pulled up suddenly, which would necessitate a very strong chassis to lie fitted, also very strung pNE LF^rsq FLQ£ST. Diagram B. floats. Again, with this type, in the case of a steep nose dive the reaction of floats with the greatest centre of buoyancy at the rear would tend to increase the dive instead of damping it. Mr. F. Whitworth has since the discussion sent us the following communication, which we insert herewith, together with diagrams A and B :— "There is one point about hydro-aeroplanes which strikes me, and that is, that the last part of the float to leave the water must be in front of the centre of gravity, or else the model must be supported on three floats as per diagrams. I think that this also works out in practice. In models with two leading floats, the tail float usually rises first, and the machine's run is made on the two front ones; in the other type, with one float in front and two behind, I think that the model's final run is on all three floats. My idea is that the last reaction is at the e.g. of the model. On one of mine (the only one which I measured in this way) the model had two leading floats, and I found that with the best disposition of 525
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