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Aviation History
1927
1927 - 0170.PDF
MARCH 10, 192: THE HANDLEY PAGE SLOT-AND-AILERON LATERAL CONTROL Greatly Increased Safety Attained " THE case of the slotted wing is very important. It is, I think, true to say that it is the only real aerodynamical discovery of the last decade, and was undoubtedly a brilliant invention." This sentence, quoted from one of a series of articles by Mr. J. D. North (THE AIRCRAFT ENGINEER, June 24, 1926) related to the Handley Page slotted aerofoil in which the slot extends over the whole span, and not specifically to the use of wing-tips with slotted leading edge, but if Mr. North's remarks were true with reference to the complete slotted wing, they are, perhaps, even more so if applied to the combination of leading edge slots and ailerons of various types for lateral control at or beyond the stalling angle. .Let us go back to the commencement of flying, and examine briefly the history of lateral control. When, in 1903, the Wright Brothers first succeeded in making controlled flight possible, they did so by a system of inter-connection of wing warp (used by them instead of ailerons for lateral control) and rudder, and the original Wright patent covered this inter-connection, showing clearly that these great pioneers of aviation had early discovered that lateral control required type. As a result of these tests it was reported* that " th.- use of the variable slot in conjunction with ailerons has been found to give a control which is greater than the sum of th, controls obtained with each separately, and which at larg> angles of incidence is not very far short in magnitude (ex pressed as a coefficient) of the control given by the ailerons alone at normal flying angles. Such increased control is obtained, together with considerable decrease in the yawing moment to be overcome by the rudder." In 1924 slot control was fitted on an Avro biplane having Frise type ailerons. The official report on the tests"j" states : " There is no doubt that this form of control has greatly increased the safety of flight in the region of the stall. It could with advantage be applied to fighting aeroplanes. There is no measurable loss in performance due to its use." The Stability and Control Panel investigated the problems of lateral control of stalled aeroplanes, and issued, in 192H, a report (Reports and Memoranda No. 1,000) in which the conclusion was arrived at that " there is little doubt that the new control has added greatly to safety in flight in two respects—firstly, in enabling the pilot to counter the incipient GETTING OfF OR LANDING Diagrammatic representation of Handley Page Slot Control. " opposite rudder " to counteract the increased drag Thus they produced an aeroplane which was controllable over a certain range of flying speeds and angles, but the " stall," with its attendant spinning, was not found out until a good deal later. For years it has been known that a very large percentage— how large it is difficult to estimate accurately—ox accidents have been due to stalling (i.e., losing flying speed and, therefore, lift) near the ground, the stall being accompanied in most aeroplanes by a spin. It is also a familiar fact that an aero- plane requires a very considerable height in which to recover from a spin, the actual distance varying according to the characteristics of the machine. The type of lateral control which has become almost universal, i.e., the hinged trailing edge flaps, becomes weak, or even totally ineffective, at angles near or above the stall. Moreover, the fact of puliing down the aileron on one side has the effect of increasing the drag on that side, thus tending to swing the aeroplane around in such a way as further to increase the bank. The exact opposite effect is desired. Shortly after the war Mr. F. Handley Page in this country and Herr Gustav Lachmann in Germany hit upon the idea of the slotted aerofoil, the two inventors working indepen- dently, and one without knowing anything about the work of the other. The original object of the invention was to give increased lift for a given area. It was not, however, long before it was realised that the slotted wing had possi- bilities as applied to lateral control, and the Handley Page firm carried out a considerable amount of research and experiment in this direction. Ultimately the Aeronautical Research Committee interested itself in the problem of slot controls, and work was carried out on wind tunnel models. This was sometime in 1922. In this instance the leading edge slot was used in conjunction with ailerons of normal spin, and, secondly, in helping him to get out of a developed spin." Recently yet another report on tests has been published! in which the conclusion is expressed that " the feeling of safety when coming slowly in to land is very marked. The increase in control at slow speeds, especially on steep turns, has probably considerably improved the aeroplane's fighting efficiency. In two mock fights carried out at the R.A.E., in which the pilots were interchanged between the flights, the Bristol Fighter with the slot control outmanceuvred the standard aeroplane on each occasion." By way of testing the slot control on a machine of a very different type, a de Havilland " Moth," with 60-h.p. " Cirrus " engine, was fitted with this control and tested at Martlesham Heath. The report of this establishment states that " The aircraft is very easy to fly, and in respect of handling qualities is very suitable for instructional purposes, particularly when fitted with the ailerons with slots, which almost eliminate the risk of serious accident through inadvertent stalling." We have now reached 1927, and the evidence which has been accumulated all goes to show that the slot control in conjunction with ailerons provides powerful control in the stalled state of the aircraft. That being so, surely the obvious line of development is to fit the slot control on really fast machines for the purpose of ascertaining whether any unfore- seen difficulties arise. If not, the logical result would seem fgto be the fitting of slotted lateral control to all types aircraft. It might be argued that control in the stalled state d> 'S not constitute a cure of the stall itself. While that is true it is equally true that the stall loses most of its dangers controllability is retained. We do not wish here to go i' * Reports ard Memoranda, No. 856. t Reports and Memoranda, No.t Reports and Memoranda, No. 1,051. » 150
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