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Aviation History
1933
1933 - 0452.PDF
SUPPLEMENT TO FLIGHT 56 THE AIRCRAFT ENGINEER AUGUST 31, 1933 facts to differentiate between the Zap ailerons and the conventional and floating types. Previous to the de velopment of the Zap aileron, any attempt to use a trailing edge flap was immediately handicapped by the fact that from a half to two-thirds the span was used for lateral control, thereby diminishing the available maximum lift-increase. When evaluating their respec tive merits with any tvpe of lateral control, there are two conditions of flight that must be considered: control above the stall and below the stall. With the conven tional aileron, if the plane is approaching a landing in a glide above the stall but very close to the maximum lift, and a wing is unavoidably dropped when the aileron is moved to a positive angle with the idea of picking up the low wing, several conditions are to be observed. Any small deflection of the aileron is reflected in a change in the lift on the major airfoil. This is of distinct advantage, because small aileron surfaces can be made to produce a rather substantial rolling moment by influencing the flow over the major airfoil. The con ventional aileron, however, is at a disadvantage in that a large movement of the aileron might create a resultant angle of attack that would be beyond the critical angle and cause the wing to stall and further accentuate the dropped wing condition. Simultaneously with this, due to the unfavourable yawing moment, the wing tends to rotate backwards and still further decreases the lift with the possibility of entering a spin. Any further positive movement of the aileron only aggravates the stalled condition from a standpoint of flow over the major air foil and at the same time induces further unfavourable yawing. We will compare this with the floating aileron and later the Zap. In the condition where the aeroplane is approaching the ground, close to the point of maximum lift, but with floating aileron, if the wing is inad vertently dropped a positive deflection of the floating aileron will create an increase in lift, but only an amount equal to the lift generated by an airfoil of that particular aileron area and section wing naturally affects the flow over the top surface. Analysing the several conditions, as was done in the case of the con ventional floating ailerons, we find that if the aeroplane is being brought in close to the point of maximum lift and the wing is inadvertently dropped with a positive movement of the Zap aileron, there is not only created a rolling moment by the increase in lift on the aileron acting as an airfoii section alone, but there is also an induced lift on the major airfoil together with a yawing moment that is slightly less than the conventional aileron. (See Fig. 9.) At or below the minimum flying speed at which an unflapped aeroplane can fly, by reason of the fact that the Zap ailerons are used in conjunction with Zap flaps, the aileron is actually operating in an area of stimulated flow and consequently produces favourable rolling moments at speeds far below the speed at which a conventional wing aeroplane can be controlled with Frise or floating types. Even without the effect of stimulated flow due to the flap, the ailerons produce rolling moments comparable with conventional ailerons per unit of area. It must again be borne in mind that conventional ailerons cannot be used efficiently with flaps located across the entire span of the wing by reason of the fact that they would be blanketed by the flap. If they are used, the flap can only occupy the inner portion of the span. At the reduced flying speed accomplished with the aid of any slow speed device which is below that of the minimum flying speed of an aero plane without flaps, the conventional aileron is all the more ineffective by reason of the fact that it is operat ing in a reduced flow of air, whose velocity is only to that of the plane and not the stimulated flow over at that particular angle of attack. There would be no induced flow over the surface of the major wing. In designing such an aileron, this would have to be taken into consideration, and the aileron would have to be quite large so as to produce within itself a practical rolling moment at the reduced speed of flight brought about by the use of flaps or any other slow speed device. The resultant aileron, by reason of its size, would then present very difficult structural features, as well as added weight and drag. This type of aileron naturally would have no bad effect of aggravating the stalled atti tude of the dropped wing either when the aeroplane was coming in slightly above the stall or beyond and would have still further the advantage, by reason of the angle of its lift vector, of a favourable yawing moment that would tend to pull the low wing forward and increase its velocity and consequently its lift. With the Zap aileron, the first reaction is that it is just another airfoil suspended above the wing of which there have been numerous designs in the past. The original Curtiss type was mounted at a considerable distance from either surface of the wing and through its angular movements produced a workable rolling moment. These ailerons went out of existence because of the fact that they were inefficient. They induced no increase in lift over the major airfoil sections and if they were large enough to produce a usable rolling moment, their drag, mechanism and structural features were decidedly objectionable. Preliminary investigation indicates that Zap ailerons will also be quite interesting in any slot and flap application in the future. At this point I might give some of the practical reactions that I have had in flying Zap-equipped aeroplanes, and ask your patience while indulging in a little elementary theory of flying. There is no doubt that reduced minimum speed, with adequate lateral control and good inherent stability, will materi ally lessen the fatal crashes in aviation. In the majority of instances, fatal crashes occur from flying too slowly or gliding into a forced landing immediately after motor failure. The loss in lift at a speed just below the minimum naturally causes the aeroplane to mush with a consequent increase in the resultant angle of attack, which, when beyond the critical angle, results in a critical loss in lift and altitude. The reason for flying slowly is brought about by the fact that the pilot is forced to do so in order to get into a given aerodrome over surrounding obstacles. Realising that the modern aeroplane glides so flat and so fast, as is becoming more evident each day with the cleaning up of designs and increasing wing loadings, and in attempting to consume the smallest possible amount of aerodrome while in the glide, and also after levelling out, the pilot invariably brings the plane in as close to the point of maximum lift as he feels that he is capable of doing—and the better the pilot, the more likelv he is to feel that he can plov close around the stall point. If a sudden gust, or inattention on the part of the pilot, inadvertently brings the flight attitude over the critical angle, a crash is likely to result and the impact with the ground must n very close to the minimum flying speed of the snip, which, as assumed, is already very high. The pd' cannot put his nose down after coming in over obstacle and pursue a steep angular path to the ground at a safer angle of attack because of the large pick-« in flying speed. This increase in speed would prolong the path of flight tangential to the ground which almos invariably results in a high speed two point landing. With a Zap equipped aeroplane, it is not necessary the pilot to bring the aeroplane in close to the poin of maximum lift, as far as excessive utilisation or aerodrome is concerned. The Zap equipped aeropH"1 , because of its high lift and drag, can be brought in along a flight path that is so steep as to permit on a small utilisation of available aerodrome dls^an"ee Even when the nose is put down at a 45 or 50 deg _ angle, the increase in speed is small, and when aeroplane is levelled out, the drag causes it to deceler very rapidly and the high lift permits a slow mmlft[, ^ speed when it drops on the ground. It might be poin • out that the steep approach to the ground is a ois ^ vantage from a standpoint of the technique requiret 870 d
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