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Aviation History
1951
1951 - 0638.PDF
396 FLIGHT Models of (above) the Saunders-Roe Princess, with four Coupled Bristol Proteus and two single Proteus, and the Duchess (four de Havilland Ghosts). The Duchess is designed for a gross weight of 130,000 Ib and should cruise economically at about 470 m.p.h. ON FLYING-BOATS . . . flew much less surely than did the contemporary aircraft because of the increased air resistance and weight of the floats as compared with the skids or wheels they replaced. This defect showed up either as a reduction in carrying power or in perform- ance. Despite this it was not very many years before the world's speed record was captured by a seaplane. It will be suggested that this was because of the money, and therefore the research, put into the winning of the international Schneider Trophy Race and that, had a similar prize been offered for the fastest landplane*, the landplane would have held pride of place. I think this is unsound logic unless the prize had been enormous for, in addition to the cost of producing the landplane and engine and all the other bits, it would have been necessary to provide the aerodrome from which it could operate. It would have been essential to make the landing chassis retractable; not a very easy problem with a thin-wing biplane, which for a long time held supremacy over the mono- plane. Fuselage space, into which the wheels conceivably might have been retracted, was limited. Indeed, the floats of the sea- plane were found to be most useful for the storage of fuel and as cooling surfaces. We were not dealing with self-cooling jets then, and disposing of the heat generated by those powerful racing engines was one of the bigger problems. The flying-boat, despite the handicap of facing less competition than its landplane rival, because it was produced by fewer firms and in smaller numbers, held its performance superiority until the coming of the cantilever monoplane with variable-pitch airscrews and retractable chassis and—perhaps the most important aid of all —the provision of hard runways of sufficient length to enable advantage to be taken of higher landing and take-off speeds. So flying-boats have been slower, then faster, and now not so fast as their rivals. Who is to say that history will not repeat itself? Finer Points Without regard to the question concluding the last paragraph, the flying-boat can be a thing of beauty and a useful piece of apparatus, and I would like to say something about its finer and lesser-known points. The reader may have gathered already that it is my contention that the flying-boat of 15 or 20 years ago was more advanced than the landplane. It was much more nearly analagous to the modern aircraft with retracting tricycle undercarriage. The air resistance of the hull with faired steps was considerably less than a fuselage-cum-fixed-landing-chassis. It floated at rest with the hull roughly level, a feature not perhaps fully appreciated at the time, but it was a great asset to the maintenance engineer and a great comfort to the crew and passengers. The risk of blowing over at moorings was almost entirely eliminated. It had stable directional qualities, of which more anon. For the benefit of those who have not had boat experience I will describe, very briefly, a typical take-off. As speed is gained on the take-off run, the hull attitude, and;, of course, wing incidence, becomes increasingly greater, and there- fore much of the load is, early in the run, transferred to the wings. In this way a quicker take-off is achieved, for no hull within my experience has a better lift/drag ratio than about 5:1, whereas wings may realize easily a figure of more than double this. By the term, "hull lift/drag ratio", I mean the weight supported by the • In the original article the term "land aeroplane" is used here, and, subsequently, "aeroplane". We have taken the liberty of changing this to "landplane" when it appears that the author is using it in contradistinction to "seaplane" or "flying-boat", otherwise misunderstanding might be caused. Possibily Mr. Lankester Parker dislikes the word "landplane ; so do vie— but nobody has offered an acceptable alternative in 40-odd years.—ED. hull bottom (or, if you prefer, gross weight less wing lift) against water resistance. As speed (we are still on the take-off run) further increases, the hull attitude tends to get rather less, again so that the final "unstick" is made not at the stall, but at a speed about 1.2 times greater. The foregoing is a description of what might be expected to take place as the result of natural running, though, in fact, the pilot has a considerable degree of control over attitude at all times. He would, of course, also have to maintain course and possibly keep laterally level as well. The good boat of the period I have in mind was directionally stable on the water, a quality surely not possessed by any non- tricycle aircraft chassis. Perhaps I make too big a point of this, and I do agree that a directionally unstable hull or chassis does not necessarily make the aircraft, or flying-boat, unacceptable. Such a chassis or hull fitted to an otherwise good aircraft, suitably finned and ruddered, braked and throttled, and so on, can be made to do most anything, including take-offs and landings out of wind; but that does not imply that the hull or chassis is itself stable or, may I say, a good one. To avoid any misconception I define directional stability, whether in a hull or a chassis, as that quality which causes the said hull or chassis to tend to turn down-wind when proceeding across-wind—in opposition to the weathercock tendency of the aircraft as a whole. For the same geometrical reasons it tends to oppose any swing or change of direction forced on it. There is still one other great difference between a normal flying-boat and an aircraft on which I have not yet touched. As I have tried to show, the flying-boat has many qualities in common with the tricycle-chassis landplane but, I want to carry the analogy to its limit, to a one-wheel "tricycle," if I may be forgiven the term. This arrangement has some virtues as well as disadvantages. The virtues are mostly from a structural point of view; surely it is better fundamentally to have only one point of major force application, as when supporting the weight of a necessarily ungainly device such as a large aeroplane out of its natural element, on the ground. One has only to look at a swan or a sea lion on dry land to see what I mean. Especially is this so if, as with a flying-boat, the forces are distributed evenly and gently over a large area rather than con- centrated at certain fixed points. Large racking strains, inherent in twin hulls or two wheels, are avoided. There are, of course, snags. One of the greatest difficulties confronting the flying-boat designer is to achieve lateral stability on the water, both when at rest and when taxying. The nature of the beast renders it impossible to get shiplike stability; the metacentric height is much too high. There have been three major lines of research into lateral stability : (1) the double-hull or twin-float seaplane; (2) the single hull with sponsons or water-wings; and (3) auxiliary floats along the wing, usually called wing floats. With the twin-hull arrangement most of the structural advan- tages inherent in the flying-boat disappear. Seaworthiness is, in my own experience, very greatly lessened. I suspect air drag may be high. Sponsons have undoubtedly some great advantages over either of the other methods and were much favoured in Germany, but they also have some very serious disadvantages, of which I will list a few (not in order of importance), namely, greater air resistance, greater weight, and being more prone to damage by rough seas when taking-off or alighting. I believe they are good on rough seas once the boat has come to rest. But the major defect of the sponson method is that it fails to provide lateral stability under certain conditions, such as when taxying at that particular speed when the sponson itself is neither planing properly nor is an effective buoyancy float. So far as I know, no design of sponson yet produced provides the lateral stability at all speeds, thought
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