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Aviation History
1954
1954 - 0332.PDF
158 FLIGHT HELICOPTER FORUM . . , possibly have been in reference to military aircraft. There was no reason why, given the opportunity, British blades should not eventually reach such a figure. MR. FRISE agreed, saying that, primarily, two things had to be done to increase life. One was to find something which would stop them from warping or changing their shape, such as corrosion by rain. This happened a lot to composite blades; it brought in vibration and then they had to be scrapped. The other thing concerned was fatigue in materials; those most suspect at the moment were light alloys. The most direct attack on the problem was to use stainless-steel blades. With very few exceptions, pilots' controls in helicopters seemed to be designed as a curious modification of those on fixed-wing machines. There is virtually no transfer of skill, so is this necessary? Could not the controls be designed on principles derived from human engineering studies into the most natural and ergonomic system of human control over a multi-dimensionally-free machine? If previously learned skills and habits are of value to a helicopter pilot, why not use the control system of the motor car as a model? MR. REED said that this was a sore point with him. One tended to get away from the fact that a helicopter was an aero plane and came under the normal rules and regulations of orthodox aircraft. He could see no reason why an attempt should not be made to make it like an orthodox aeroplane from the point of view of normal controls; it was unnecessary to have extra controls. A desirable feature of design was a constant-speeding rotor, and once we had that we would do away with the throttle-cum-pitch control and return to a normal throttle lever; the collective lever in itself was the only difference from normal aircraft control. If one had a throtde and a constant-speeding rotor then the only difference would be in take-off, landing and emergency techniques. MR. SHAPIRO recalled one design for which a very different control system was used—the Hoppicopter, in which a single control-organ did virtually all the controlling. It was arranged in a manner which seemed very logical, inasmuch as every motion of the aircraft was initiated by a replica motion of the hand of the pilot. He had closely interviewed the pilot who had had a great deal of fixed-wing experience, but no helicopter experience; this man had taught himself to fly on the machine. From this experience, said Mr. Shapiro, his interpretation was that any control system was possible. He did not think we had enough comparative studies to arrive at a really well-founded distinction between control systems; in the past, departures from the orthodox method had been resented by pilots. What would happen to a novice on helicopters? He would not be likely to resent a new kind of control. The speaker believed there was very litUe to choose, and he could not see there were enough reasons to depart from what had already become conventional systems on helicopters. (Part 1) Has any headway been made recently regarding blind-flying instruments? When will suitable instruments be available for commercial use, and in what way will they deviate from those used in fixed-wing aircraft. (Part 2) Sup posing that the stability, instrument and automatic flying problems will be solved, and remembering that helicopters may be expected to operate in relatively close proximity to obstacles and local terrain, is there any reason to assume that limits for bad-weather operations will be lower than those for fixed-wing aircraft? MR. REED said that there ought to be improvement in attitude- indication for the fore-and-aft condition of the airframe. At the moment the aircraft could apparently be climbing, yet in actual fact it was descending with nose up and tail down. That would be indicated on the present orthodox horizon, but by utilizing the rest of the instruments one would know what was going on. With orthodox instruments used collectively it was impossible to get into a position in which "you do not know where you are"; but it would take a lot of sorting out. DR. HISLOP said there was no doubt that, to be worth while, commercial helicopters must be capable of flying at night and in bad weather conditions, probably to considerably lower limits than fixed-wing aircraft; and, from the experience of which he had knowledge, he thought there was no special reason why this could not be achieved with what were substantially orthodox instruments modified to suit the particular helicopter characteristics. He was very doubtful if there was a pressing need for any completely new instrument. Where the A.S.I, was concerned it was a question of finding the correct source of static pressure. He believed an instrument could be obtained which would give satisfactory indication down to the speed range that was set. When the speed on a blind approach fell to 10 or 15 m.p.h., or even lower, the pilot would also have other assistance, such as electronic aids, to keep him on the correct heading and correct rate of descent. MR. FRISE said that the designer's job was to make the heli copter very easily controlled and so stable that the problem of having an automatic control when on instruments was simplified. MR. WHITBY, answering Pan 2 of the question, said that the helicopter could operate to lower limits, generally speaking, but not in what was really the important matter—that of cloud ceiling. Being conservative and looking into the immediate future, he could not envisage anybody coming into London to land at a "submerged" site (or, for that matter, an elevated site with spires in the vicinity) when cloud was on the deck. He thought there would always have to be a fairly substantial cloud ceiling—in the order of 300ft—and blind flying would then primarily become a problem of moderately low-speed cruising, flying blind. In these circumstances, so far as one could make out, and if the flying characteristics of the aircraft were improved, the existing basic fixed-wing blind-flying panel would be adequate. It would not be so if one attempted to hover or fly at very low speed without external reference, but he was not convinced that this would be a necessity. Obviously, the pilot approaching with any sort of wind, was going to get an entirely wrong impression of his flight path if he was flying at the speeds indicated by his A.S.I. Air speed was not of great importance to flight path at low speeds. MR. REED said that the matter really revolved around stability. If stability was comparable with that of the fixed-wing machine it would be easier to say "yes" to the ordinary blind-flying panel. City planning and the various means of surface travel are already inadequate to meet traffic requirements. The heli copter provides the future answer to most problems of speedy transport from one part of a city to another, and from city centre to airports. But if a city were to be designed from the outset to take advantage of projected means of surface transport, diesel trains and cheaper electricity from atomic power, would the helicopter be likely to prove as economical or even as fast as surface alternatives? DR. HISLOP said that were a city being planned from the outset —he cited a new city being built in India—an airport on the outskirts could be served by a surface transport system which would be almost as fast and certainly more economical for trans port of large numbers of passengers than a large helicopter. That might sound heretical, but he thought it could be done. One could visualize the equivalent of an express tube or surface train system which could cover the distance in a very short time and very economically. MR. WHITBY was broadly in agreement but said the initial outlay of a tube system was expensive. Above-ground trains were much cheaper, but he thought it cost about £1 million a mile to build a railway. It would probably be worth while, however, in the long run. MR. SHAPIRO dissented from this view. A curve demonstrating the power required to propel a motor car showed that at about 80 m.ph. most of the power was absorbed in overcoming air resistance. The same thing applied to a helicopter and, for that matter, to an aeroplane. This resistance had to be overcome, whatever vehicle was considered; and the remainder, which was small, was all that mattered in the difference between the motor car, the helicopter, the aroplane and the train. He did not believe that this small difference could make up for the enormous instal lations which would be required to bring surface transport to the speed of a helicopter or an aeroplane. Does the Brains Trust agree that present-day helicopters, and those which are likely to appear in the foreseeable future, must inevitably depend for their safety on a rotor system subject to intense cyclically-fluctuating stresses? If so, does the panel agree that the helicopter must be considered for some time as inherently less safe than a fixed-wing aircraft? MR. WHITBY said that this was really a design matter, but the helicopter must, he supposed, be inherentiy less safe. This did not mean that, provided one was prepared to pay the penalty in extra robustness to have a reserve factor to cater for any fatigue, the helicopter could not be made practically as safe as fixed-wing aircraft. That was one of the economic penalties which the helicopter had to pay for the ability to fly at low speeds. DR. HISLOP thought that this question had a bearing on that concerning the A.R.B. and life of rotor blades. If we could design blades to give satisfactory lives of the order he had mentioned earlier, the general safety-level in cruising flight would be com parable with that of fixed-wing aircraft. He was sure that, when close to the ground, the helicopter was very much safer than a fixed-wing aircraft ever would be. In the long run it would be shown that the helicopter was a safer vehicle. MR. REED asked how one came to a conclusion as to what a degree of safety was. The only way in which one could say that the helicopter was less safe than the ordinary aeroplane was if we had had accidents caused by cyclical oscillations; and he could not think of one. MR. SHAPTRO heartily agreed with Mr. Reed. Nine-tenths of all accidents had non-structural causes, and in these the helicopter was so much in advance of fixed-wing types that whatever dif ference there was in structural matters was completely insignificant. (The remaining questions and answers mill be printed next week)
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