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Aviation History
1931
1931 - 0002.PDF
FLIGHT, JANUARY 2, 1931 added to the landing speed probably does not increase risk to any appreciable extent. In the case of air- craft for the private owner, the position is somewhat different. The future will probably show two classes—not, of course, with a very marked distinc- tion between them—the private owner of consider- able skill, who can safely handle the faster machine, and the less skilled owner who, for real safety, requires a type which he can " put down anywhere." Thus, the high-efficiency type towards which we are now definitely tending will always be wanted, and will continue to develop. But just as certainly, a different type, not, perhaps, quite such a " thorough- bred," will be required for the man who wishes to fly in comfort and safety, but who has no aspirations to achieve the skill of a Schneider pilot. To such as he, the greatest risk is still the stall and the spin which is ever likely to follow it. Low stalling speed , reduces the risk a little, because the lightly-loaded machine does not lose as much height in recovering, - but it does not altogether avoid the risk. The only way to do away entirely with the dangers following • the stall is obviously so to design the machine that it cannot be stalled. Then, if the machine descends :: approximately on an even keel, it becomes largely ; a matter of undercarriage design whether no damage is done, or but little damage.: At the present time there are three distinct solu- tions in sight, all avoiding the stall and spin : The tailless type, the Cierva Autogiro type, and the tail- first type. (We are not including here the Handley- Page automatic slots because, although they do prevent the incipient spin, they do not prevent the stall.) Each of the three types mentioned has something in its favour, and something against it. It may be of interest to examine very briefly the main characteristics of the three. The tailless type of aircraft is represented, as far as this country is concerned, chiefly by the Westland- Hill " Pterodactyl." The principle upon which the design is based is to sweep the wings back at a pronounced angle, and at the same time gradually to decrease the angle of incidence from the centre of the wing towards the tips. The centre portion, being at a greater angle than the tips, reaches stalling before the outer wing portions, and so the wing as a whole loses lift but very gradually; and not suddenly, as in the orthodox straight wing. In the " Autogiro," Senor de la Cierva makes use, for his lifting surfaces, of rotating blades which are kept in motion by the air forces upon them. This makes it possible for the machine as a whole to remain almost stationary, but descending slowly, while the lifting surfaces continue to revolve and, therefore, to give lift. The all-but-vertical descent of the " Autogiro " cannot be quite equalled by any type of fixed-wing aircraft. In the " tail-first type of machine, such as the Focke-Wulf " Ente," described and illustrated in this issue, the fundamental principle of design is that the load is divided between the main wing and the forward wing, the latter being much smaller than the main wing and, if the same aerofoil section be used in both, more heavily loaded per square foot of surface than the main wing. Thus, at any given speed, the forward wing must be at a greater angle of incidence than the main wing, in order to carry ts load. The result is that the forward wing reaches tailing angle before the main wing does, the nose and the machine gathers speed. The fact that, during the stalling of the forward wing, tht main wing is near its angle of maximum lift, mean^ that the drop of the whole machine is probably small, and little height is lost before the machine is again flying normally. Each of the three types has certain good features, and each has, as is but to be expected, certain draw backs. There is no space here to go into great detail, nor is the Leader Page the proper place for a technic- ally exhaustive treatment of the subject. But to help the more non-technically minded among our readers to a general understanding of the subject, it may be pointed out that the " tail-first " type of air- craft succeeds in avoiding the stall, and should be as efficient, aerodynamically, as the orthodox aircraft, but is a little difficult on the ground, where it is turned over as easily as is the normal type of machine. The " Autogiro " also is a little difficult on the ground, chiefly because of the impossibility of suddenly stopping the speed of the rotor blades. Thus a strong gust of wind striking the machine after it has landed, but before the brakes have succeeded in stopping the rotor, may turn the machine over. Against that drawback, however, must be placed the unique ability of the " Autogiro " to descend, nearly vertically, into a very restricted space. A forced landing can, in fact, be made with this type of machine in spaces which would be utterly impossible to ordinary aircraft, and to the " tail-first " type, although the " tailless " might approach it somewhat. Aerodynamically the " Autogiro " cannot readily be compared with the orthodox type, not because it is necessarily markedly inferior to it, but because its maximum efficiency occurs in a different part of the speed range, i.e., nearer the top and bottom ends of the speed scale. The " tail-first " type can claim immunity from stalling (as it is ordinarily understood) and spinning and it would seem to score over both the " tailless " and " Autogiro " types in its stability on the ground. Owing to the fact that so much of the machine pro- jects ahead of the centre of gravity, even the locking of the wheels by means of the brakes, or alighting on very rough and soft ground into which the wheels sink, will hardly turn the machine over. Thus it seems reasonable to assume that, provided the emergency landing ground is large enough, the " tail- first " type will make a safe landing. It is not likely to be able to get into as small a space as the other two types, because its very stability would seem to prevent it being brought down at low speed along a steep flight path. The Focke-Wulf " Ente " described this week is disappointing both in aerodynamic and structural efficiency, but we cannot believe that this is inevitable in the " tail-first " type, and is probabh due in this case to the experimental nature of the machine. One not unimportant point is that it should, theoretically, be possible to save weight as compared, for instance, with a flying boat. The high centre oi thrust in a flying boat has to be counteracted by a considerable down load on the tail. In a large flying boat this may amount to 1,0001b. or more. This weight, of course, has to be carried by the wings. In the " tail-first " type not only is this weight saved but the forward wing helps to carry its share of th< weight. Without wishing to prophesy, and without belittling at all the respective advantages of the " tailless " and " Autogiro " types, we believe that the " tail-first " type is worth developing also in thi- country.
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