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Aviation History
1930
UNTITLED0 - 0030.PDF
FLIGHT, JANUARY 3, 1930 element is beginning to feel the effects, for a temporary blindness is not unknown as a consequence of rapid turns. There exists an excellent instrument for measuring these loads which arise from centrifugal accelerations, and it is well known that loads three times normal are frequently met with. Five times the normal weight is not uncommon, and in specially designed aircraft pilots making an attempt have reached 10 times the normal loading. It is clear that this loading is near the limiting strength of the human structure, and it is probable that—given an aeroplane which is stable at high speeds—the physiology of a pilot will limit the overload to something more nearly 5 than 10, except in an extreme emergency. Approach to the ground at high speed is the one emergency calling for maximum use of the strength of the craft. Such considerations have led to a system of load factors to which British aircraft must conform, in order to comply with the law. A load factor of eight is not difficult to achieve, but this corresponds with a factor of safety which may not exceed 1$, and for this reason aeronautical engineering is more specialised than its predecessors. Best materials, best methods of calculation, workmanship and inspection are required. These conditions were foreseen as early as 1910, and suitable organisations were called into being. It happens inevitably that the problems of yesterday which have been solved seem to be simple, but it is almost certainly true that aerodynamic research is now much more complex than it has ever been. The problem of " flutter " has become important with the introduction of high speed. It is not entirely a new phenomenon, except in its more general incidence. One of the first airscrews tested on the whirling arm at the N.P.L. fluttered. During Bush's experi- ments on the B.E.2 aeroplane at Farnborough wing flutter occurred, and the pilot's hand was knocked against the sides of the cockpit in the violence of the movements. Tail flutter had been observed in a large biplane, and a sufficiently general theory to allow for elimination had been found before 1916 was ended. Recent flying showed dangerous stresses in aircraft due to flutter, and at the request of the Air Council a new enquiry was set on foot by the A.R.C. The Royal Aeronautical Society recently arranged a lecture by Mr. Frazer of the N.P.L., at which the conclusions were illustrated very effec- tively by special models. The enquiry was mathematical on one side but the conclusions are simple and practical; whether it be wing flutter due to ailerons, etc., or tail flutter due to elevators or rudder attention to the mass distribution during design will ensure freedom from trouble. The authors of the A.R.C. monograph on flutter applied their knowledge to the Schneider Cup racers. The mathematical analysis was required to point the way and to ensure a treatment as complete as our capabilities allow. At the outset it was not clear that success was attainable on those lines, and an alternative attack was simultaneously pursued. The Royal Aircraft Establishment suggested the use of a scale model in which the scale was extended to cover elasticity of parts as well as their geometrical form. An examination of the details showed the practica- bility of the method and a model of an aeroplane which flutt.-. (1 in flight was made and tested with entirely conclusive results. Prediction is possible along these lines and it is fair to conclude that aerodynamic knowledge is now adequate for the prevention of flutter. Another old problem has come up for further consideration, that of spinning. It will be within the recollection of many that much trouble was caused twenty years ago by stalling and spinning, although the trouble was expressed in other words. FLIGHT will show you in its early volumes an account of an event called " Parke's Dive." For years " stalling " ended the explanation of this danger, but a series of enquiries by the accidents investigation committee of the A.R.C. led to the discovery of autorotation and its calculation. It at once became apparent that the elevator was an important organ of control in correcting the consequences of spinning. Elaborate manoeuvres, well above the ground, were made with confidence, whereas 21 years' ago turning was an adven- ture, looping and upside down flying unknown. The next step was the enquiry which led to the slot and aileron control mentioned earlier. Each development has had its effect, but more is needed ; as the old manoeuvres became safer pilots extend their range and new difficulties are encountered. It may be newness only, but with our present eyes the prospect is forbidding. The technique in the laboratories is being extended beyond previous limits in an attempt to find an understandable solution of the remaining difficulties. Small models in Balsa wood are being made and fitted with fuses which operate the controls at appropriate moments in order to test devices for recovery. The way may be long but the method of scientific enquiry is powerful. The aerodynamic problems connected with airships have not proved to be formidable. In spite of their great size and the consequent difficulty of reproducing full scale eo»- ditions in a laboratory, there has not been any failure t« give the guidance necessary for design. This may be fortuitous. Indirectly, aerodynamic considerations have had a fundamental effect on the design of our two new airships R 100 and R 101. Prior to them, airships had been designed primarily on a basis of static forces, but the failure of R 38 in flight brought to light the inadequacy of this basis. A series of investigations was undertaken and a new set of design conditions deduced which were based fundamentally on a consideration of all the factors involved. It was not possible to foresee accurately the limits of practical possibility but it did appear feasible to design an airship capable of withstanding any sort of bad weather short of that in the centre of a thunderstorm. Now that the airships are com- pleted there is no need to go back on the expectation of 1924. The exact future of airships and of aeroplanes is stillunknown, but it will be an unusual experience in the world if it lets pass any opportunity for improving its communications. For long distances covered quickly, the airship is the most promising of known means of transport. It still suffers from its infancy—the equivalent of the docks and ports of the ocean liner have still to come, just as have the municipal aerodromes, etc., for aeroplanes. International barriers are beginning to assume a new importance, and time itself is an important element in producing the final effect. At the same time the effect will come more quickly if a steady policy be pursued with the fullest insight into the problems involved. , •; ,. So far as the future of scientific aerodynamics is concerned, a future, comparable with that in electron theory seems assured, but a difficult interlude must first be faced until aviation expands into the commercial field and provides those prospects which will attract the best students. For those already in the aeronautical industry the difficulties are much the same and we can all join in the wish for the general prosperity of our country in order that our own mere selfish interests may benefit. ( ..I 30
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