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"180 AIRCRAFT ENGINEERING July, 1929 Servo Control for Ailerons and Triple Rudders Importan t and Novel Control Features Characterise the Newes t and Largest Air Liners for British Routes F.G.H. constituting a parallel motion. The th e direction shown. The resulting air pressure N interesting feature of the new Arm­ lever G is pivoted on the same axis as the on the vane E is indicated by the arrow. strong-Whitworth \"Argosy\" machines arm B, but the two move independently. KK I n Fig. 2 (iii) the arm B has moved to the shortly to be delivered to Imperial Airways Limited is a novel type of are cables t o the pilot's control wheel. left under the action of this force, applying to servo-control for ailerons and rudders. I n figure 2 are shown three outline views from th e control wire A a corresponding force above of the arrangement described, the cables increased in the ratio of their respective lever­ The \"A.W.A.\" servo unit is a simple servo K K being shown connected directly to a ages. In virtue of the parallel motion by which motor operated by the relative wind. The diagrammatic control wheel. In Fig. 2 (i) the th e vane E is controlled a movement of the arm force transmitted by it to the control surfaces wheel is central. In Fig. 2 (ii) the wheel is B as shown in Fig. 2 (iii) has no effect on the bears a practically constant ratio t o tha t applied angle of the vane E to the wind. The arm b y the pilot, the ratio being variable through moved t o the left, causing th e vane E t o tur n in B therefore moves until a very wide range. th e tension on th e cable The movement of the A due to the corres­ control surfaces corre­ ponding movement of sponds to the force th e ailerons balances applied to them and is th e force on th e vane. no t directly propor­ tional t o the movement The pilot feels only of the pilot's control. the force required to I n Fig. 1 the unit is rotat e the vane, and shown diagrammatic- this may be made of ally in a form suitable an y desired magnitude for operating the ailer­ b y suitable disposition ons. A represents one of the pivot D on the of the cables of the vane. The force applied normal circuit connect­ t o the control depends ing the right and left on the leverage of the ailerons. It is divided arm B, in addition to and attached to B, a th e size of the vane. horizontal arm which is I t may therefore be pivoted at its forward varied within wide end on C, a vertical limits, and large sur­ axis fixed to some con­ faces may be operated venient part such as b y small forces applied th e front spar of the t o the control wheel. wing. At its after end Since the position of B carries D a vertical th e centre of pressure spindle, on which is of a symmetrical aero­ mounted E the servo foil such as will be used vane, by whose move­ for the vane E varies men t relative to B the very little, the air force required force is applied on th e vane will be prac­ t o the operating cable tically proportional to A. F is a double arm th e force on the pilot's of the conventional hand. Thus the force type , connected to G a applied to the control double lever of equal surface (through the length by HH two cable A) will bear a cables, the system (continued opposite)  July, 1929 AIRCRAFT ENGINEERING 181 Serv o Control—(continued from previous page) pilot's movement of the pedals. Its axis is practically fixed ratio to the carried by levers which are connected to the force applied by th e pilot t o th e outer rudders by a link. The side force on th e control wheel. centre rudder operates the oute r rudders. For the same reason the force Any tendency to side slip will cause the required to produce a given outer rudders to move so that the machine angular movement of the con­ turn s into the side slip. The system is thus trol wheel will vary practically equivalent in effect to a fin. as the square of the air speed, giving rise t o a natural \"feel\" \" Aircraf t Engineering \" Representation in of the control free from snatch the North. or sudden change. (The servo Fro m now on AIRCRAFT ENGINEERING will be units are placed so that the represented in the North by Mr. R. Anthony vanes work in air which is sub­ Wood at 22, Bridge Street, Manchester. All stantially free from turbulence inquiries respecting advertising or any other or slip stream effects.) To matte r connected with the paper in the Man­ avoid any effect of side slip the chester and Sheffield districts can be sent to servo unit is duplicated and Mr. Wood at tha t address. arranged so tha t the vanes move In making these arrangements we ar e mind­ in opposite directions, as shown ful of th e expansion which is so rapidly taking diagrammatically in Fig. 3 . place in th e industry, and we feel that we shall The same principle is applied be rendering a better and more efficient service t o the rudders, but here the t o that part of our public which is situated in centre one of th e three rudders Manchester, Sheffield, and district by arrang­ is itself the \"serv o vane \" and ing that business can be handled directly from is directly controlled by the Manchester. "
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