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Aviation History
1945
1945 - 0084.PDF
46 " Indicator" Discusses Topics of the Day FLIGHT JANUARY IITH, 1045 lloControl Considerations The Need for New Ideas in Aileron Conception : "Unfeeling" Servo Assistance ; Are Speed Ranges Becoming Too Qreat for Conventional Layouts ? i The Possibilities of " Spoilers" and the Effect of Automatic Control on Design IT is always interesting and instructive to attempt tosort out and rationalise one's impressions after a firstflight in a new type—particularly as these first impres- sions are probably the most correct and truly comparativeof any. Later ones are coloured by circumstances, or levelled out L7 familiarity, and are not of much value. Onecan learn to like almost any kind of aircraft handling quali- ties and to prefer almost any control layout, and it is onlyunfortunate that even one's first ideas are always partly based on prejudices developed by undue familiarity withother types, Because oi this one's impressions must be rationalised if they are to be of any interest. A very large number of unimportant points tend to cloudone's judgment and we have all known occasions when a pilot has vaguely stated that he " didn't think much of it,"yet, after questioning, it is discovered that the controls happened to be on the stiff side from purely mechanicalcauses, that the throttle was erratically damped, or, for instance, that the A.S.I, couldn't quite be seen behind thegyro gun-sight. Such small criticisms have quite uncon-^ sciously given the new pilot a bias out of favour l aircraft. The Much-used Aileron Nevertheless, I' think one is right in clairpifig that thefeature which, above all others, is used tijgf basis of judg- ment more often than any other is the^aikron contjpoTTn itrelative lightness and efficiency. Thjn^frect be almost unconscious in the pilot's mind, rmtfor the very simple reason that this controKj3"vusel very much more often than any other. .It is, in feuirt, HIT almostcontinuous movement from the Jnoment of" leaving the ground, and the variation in lfghtness and heaviness^between different aircraft of the s|ime type is the cause, the often-heard remark that "there's nothing g it, but I simply don't like it; its not^a^ucejyjMrttfE/' Anyreasonable aircraft flies level without elevator attention once it has been properly trimmed, and the rudder, at anybut comparatively low speeds, is nowadays an almost unused appendage on most types; the undercarriage con-trol isn't touched once the lot has been retracted; the throttle stays in much the same place once it has beenbrought back to the rated or cruising position; and one is only briefly concerned with all the other movable itemsin the cockpit. Unless, therefore, the view is bad, the seating position uncomfortable in relation to the controls,or the aircraft definitely unstable in one or more axes, the aileron control is the only thing which can be reason-ably a cause for criticism of that vague and undescribed kind so often levelled by pilots who are not trained testpilots. And I wonder whether, nowadays, designers and othersare able to pay as much attention as they should to this vitally important item—whether, in fact, the incorpora-tion of light and adequate aileron control is becoming a little beyond the capacity of designers now that speedranges are so considerable. Probably it is. The problems are certainly immense, and difficulties are often met onlyby unsatisfactory compromises. The importance of the ailerons is still of high priority where "demonstrative"types are concerned—not so much because these controls are used more in fighter, medium bomber or '' attack ''aircraft, but because on their light and effective action over long periods depends the life of the pilot in war con-ditions—but there may be a tendency to " call it a day " where heavier aircraft are concerned and particularly wherethese are not designed for offensive work of any kind. Presumably the day of the "straight" aileron, withnothing much more than an inset hinge-point to assist it, will soon be over. Speeds are so very high and speed-ranges so great, that upfloat, overbalance, or heaviness problems are tod massive to be solved other than by theincorporation of servo devices' of one kind or another. Unfortunately, servo systems are by no means without theirtroubles and tend to remove all trace of " feel." In theory, an aileron which has very much ihe same weight through-out the speed-range and throughout its own movement, and which shows' no signs of overbalance at any speed, may bea good thing, but in practice it is far from being perfect. If it is light enough to be pelasant to use, then it can bemost dangerous in the hands of a " ham " pilot, who will happily overstress the wing structure by violent controltft4iipeds; if it is heavy enough to be safe at high speeds, fhjln it will be dull and puddingy at lowor eruising spe€3j|rNIt seems that it is difficult to arrange that a "^rfe.tiay in Veight with increased speed will bep^ate Jwith any conventional servo system, but lS^ayTbeJ^rong|libout that. ma"rina#of djtferent servo tab systems will no doubtir in sm endeavour to provide perfect control in the itenk,plaMe, jtfd it may be that quite a simple systemwill be d^isara for use in light, medium and even really heavy Jtprfa.it. With increasing speeds there are no -in-sup^raple difficulties at present in providing reasonable tl control in small and medium types, but the prob- ems become quite acute when we are dealing with whatcan only be called •'' directly assisted '' controls in large aircraft .vAdmittedly, the degree of "feel" and the dan-gers ofover-stressing by over-lightening at high speeds are not important in these, since they are likely to be handledby experienced pilots and need not be flung about the sky at any time, but for happiness in the control depart-ment, "nice" ailerons are every bit as necessary in a hundred-tonner as they are in a first-line fighter. Mechanical Automaticity Some big aircraft in the past—and many which wouldnot be considered " big " by modern standards—have been very hard work both for a human and the automatic pilot.Maybe the standard use of the latter will alter our ideas. Obviously this mechanical device will prefer the ailerons tobe of much the same weight throughout the speed-range, and it may be that the entire control system of really largeaircraft will eventually need to be based on the powers and reactions of the mechaq>£l rather than of the human pilot.The advances made during this war in automatic control systems have been tremendous and will probably alter allour ideas of transport flying technique. When the whole of the flying, from the take-off to the landing, is doneautomatically, while an engineer looks after the works and a captain stands by only to direct the proceedings, thencontrols can be as puddingy and uninteresting as need be, and only the hydraulic jacks, servos and relays need to beconsidered. In the meantime, jt might be worthwhile to consider acombination of spefler and aileron where human operation f\
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