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Aviation History
1948
1948 - 0244.PDF
2T2 FLIGHT FEBRUARY ICJTJI, TQ_)S Jkmeriean New&ietter Overdoing the Demand for Light Controls ? : Severe Conditions Met in Thunderclouds , By "KIBITZER " New York, January zqlh, 11)48T HE annual meeting of the American Institute of the Aeronautical Sciences takes place in New York during January of each year. At the same time is held the annual dinner, at which the Institute's awards and honours for the year are presented, and at which there is a guest speaker of some renown, To-day this programme of lectures, papers, and discussions conies to an end after four full days (and when I say full, I mean full, for they start at 8.30 a.m. and end at 11 p.m.), during which time the deliberations have covered the widest possible field. These discussions are often combined affairs, embracing .other institutes as well, so that the resultant joint session has a wide attendance. This year has been no exception, and papers have been read that covered such subjects as Rotating-Wing Aircraft, Instruments, Flight Propulsion oi all types, Air Transport, Navigation, Meteorology, Struc- tures, Design, Aerodynamics of the Upper Atmosphere, and similar erudite matters. Obviously it is quite impossible to give a resume of all :>? theses but there were two lectures at least which serve to show how wide the appeal was. These were, first, a series of short papers, including an open discussion forum, on the Flight-Handling Characteristics of Modern Trans- port Aircraft, and, secondly, the tabulation of the results obtained in a two-year study of thunderstorms, a combined research that was undertaken by the Air Corps, the N.A.C.A., and the American Meteorological Society. '1 the first of tflese discussions outlined the necessity for adequate controls on large transport aircraft, some of the frightening figures on thunderstorms that have been pro- duced by the All-Weather Flight of the U.S. Air Force, and which were indirectly confirmed by this second series ot papers, certainly emphasized the need, not only for good controls, but for stronger aircraft as well! During the discussions on the controllability of trans- ports, the continual and considerable emphasis that was placed on the requirement for low control loads was par- ticularly striking. By the end of the talks, one wondered whether this desire for lightness of controls hadn't assumed < r unnatural importance, and whether everyone was not suffer- ing from a hangover from 1940-1945, when such a qualifica- tion was an essential on wartime aircraft. Yet it was the most experienced among the airline pilots who called for this particular factor. Obviously light stick forces are essential (and absolutely necessary if the machine is to be controlled with only one hand on the wheel), but it does seem possible that such a quality, probably produced by power-operated surfaces, could be carried to •extremes, and that it might be as much of an embarrassment as an advantage, unless the most accurate and gentle flying were always employed. Moreover, experience indicates that, in the ordinary run of pilots, such accuracy (or passenger consideration) is noJ. always available. For example, light elevator loads might lend themselves to over-correction when landing, particu- larly under gusty conditions, and while a light machine can be "felt" on to the ground by the use of power if the attitude or height are misjudged, it is not desirable +0 do so on a transport full of passengers. It would seem that rapid and effective response to control movements are jusi as valuable as lightness of load. (Frictional loads should not be confused with aerodynamic heaviness, for the former can lead to all sorts of unpleasant stability characteristics.) Low "lb per " g'" were also considered desirable, and while this is all right on a fighting aircraft, it has its dangers because it enables undue stresses to be put on the structure. On the whole, those who were discussing the subject did not seem to be paying much attention to the other attributes which make for good handling qualities in an aircraft,, such as immediate response, good feel, harmonized controls, good view, pilot's position and cockpit layout. But, quite rightly, great stress was laid on the vital question of adequate control of the aircraft during the approach. Linked essentially with this was the demand that all extreme or sudden changes of trim be avoided flaps or undercarriage are lowered, or when power-setting! are altered. During instrument landings, by whatever system, the pilot simply cannot have his concentration upset by the necessity of continually retrimming the air- craft. He may be breaking cloud at 200 feet, or even lower, the rate of descent must be kept constant and the line of approach be kept accurately down a descent path which will bring him opposite the end of the runway at the correct height. The pilots at the meeting put forward—in support of their arguments for lighter controls—the situation where the approach path is not in line with the runway and a turn at low altitude is necessary, or when it is desirable to go around again, keeping the airport in view while doing so. The validity of these arguments seems questionable. Very light controls, when used to turn on to a runway at low altitude, might result in over-banking and hitting a wing- tip—and surely it is not correct to assume that, if the weather is thick enough to require an instrument approach which is then missed, the machine may be flown low around the airport, under the clouds, for a second try? But if such criticisms of the discussion are rather; academic, what these papers did bring out were the fol- lowing very important facts: (1) That it is absolutely essential that pilots' requirements for controllability be expressed in terms that the designer and project engineer can understand—that is—numerically and in graphic form. It was felt by the designers present that this stage is now being reached. (2) That many of the modern transport aircraft are too heavy to be controlled adequately with one hand. (3) That controls are not sufficiently responsive and in some cases inadequate. (4) That trim changes—due to various causes—are much too frequent and much too great?,, (5) That cockpits are still badly laid out. <i STORM-FLYING EXPERIENCEST HE papers on thunderstorm development dealt chiefly with the meteorological phases of such storms and less with the problems of flying in them, although the two are obviously intimately linked together. The AH- Weather Flight of the U.S. Air Force has made a great deal of study of storm-flying and have—apparently—frightened themselves no little in doing so. If newspaper reports are to be believed (and no official report has yet been released), not the least interesting point is that one never really quite knows which part of the storm is going to be the worst! Using specially strengthened and instrumented P.61 "Black Widows," pilots have made several entries into the same storm within a few minutes of one another, some- times without encountering any undue turbulence and at another time finding an area of the same storm which gave them a very rough ride indeed. So much so that cases have occurred of machines being rendered quite unservice- able as a result of the high accelerations experienced or from the battering of the hail, and of pilots being thrown about to such an extent, and subjected to such high '' g's,'' that they lost control not only of the aircraft, but of their own senses. And one machine which entered at a height
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