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Aviation History
1934
1934 - 0251.PDF
FLIGHT, MARCH IS, 19.14 A NON-FRICTIONAL CONTROL Aircraft designers requiring a light, frictionless control which is easy to instal, requires no maintenance, and has many applications, will be interested in this article R. H. S. HELE-SHAW and Mr. T. E. Beacham have designed, and the Exactor Control Co. Ltd Dorland House, Lower Regent Street, W.'l are marketing, a new form of hydraulic control the Hele-Shaw-Beacham Hydraulic Tele-Control This control has already been adopted for operating the engine throttles of certain aircraft and should un- doubtedly, in the near future, become very widely used. Its nature makes it particularly suitable for every form of control where exact movement, without any loss whatso- position of the pistons, the crank arm to which the throttle lever is fixed extends backwards and forms a cam of vary- ing radius, and working in a grooved roller on the top of the spring plunger. The bottom of this spring plunger housing is mounted on a roller, allowing it to pivot freely. By this means the spring pressure which is applied to the piston through this cam is varied according to the position of the piston, and the load on the piston is therefore kep constant. As we have already said, the pistons are packed to, anv loss whatsoever is required where weight is important, friction must prevent leakage, but in order to compensate the system be obviated, and simplicity of installation is desired. It ..-•'-. consists of two control boxes connected by a single small bore copper pipe. As it is, for the present at any rate, in aircraft primarily used for throttle controls, we will deal with it from this point of view, but designers will un- doubtedly immediately realise its many other applications. The two boxes are the same in their essentials ; our diagram showing a part section through what may be termed the transmitter. As at present arranged, the operating handle is fixed to the actuating lever, but in subsequent models the top lug on this lever is being removed and the handle will operate direct on the fulcrum of the lever. Upon reference to the diagram it will be seen that the control units have a cylinder in which a piston is operated by the throttle lever in the case of the transmitter and which operates the carburetter in the case of the receiver. This and to prevent the pistons getting out of step should leak- age occur either here or anywhere else, and also to prevent temperature changes having the same effect, a synchronis- ing device is fitted to the transmitter. In the diagram it will be seen that the cylinder communicates with a small reservoir in the centre of the transmitter through a small spring controlled valve. When the throttle is wide open, a link mechanism also opens this valve against the action of its retaining spring. This relieves any excess pressure in the liquid or, alternatively, provides for replenishment of any loss should there be any. During this operation the spring pressure on the transmitter piston is zero, but the spring pressure is still applied to the piston at the re- ceiving end ; this piston will then move to the end of its stroke as the liquid pressure has been released, thus refill- ing the system. Further movements of the transmitter piston has a specially designed gland which obviates leak- piston will be followed by exactly equal movements of the age. There is, however, a compensating mechanism in case leakage takes place either here or anywhere else in the system. The two cylinders are connected by copper piping filled with a non-freezing liquid. Both cylinders are of equal diameter and it follows, therefore, that a movement of one piston will produce an equal and opposite movement of the other piston. The fluid in the system is kept under pressure by a spring which, as can be seen in the diagram, acts at all times directly on the piston. In order that the pressure exerted by these springs should at all times remain constant, regardless of the piston at the receiving end. This, then, is a brief descrip- tion of the system as used for throttle controls. Single pipe controls are now available with a ran|*e of angular move- ment and torque transmissions. Where it is desired to provide for movement, either side of the off position, duplex units are used at each end, and the connection is by means of double piping. The throttle controls have already been installed and tested in service aircraft of the R.A.F. These control units complete, now weigh slightly under 4£ lb. and the piping only 1 1b. per 10 in., as it is no larger than I in. outside diameter. Our diagram shows the inside of the transmitting unit. The small photographs are taken from a demonstration transmitter and receiver. (FLIGHT Photos, and Sketch.) -- :;::.-: jg gj jg Jg Jg Jg • __ i • • -ft Tflryn * William Iredell, M.R.C.S., L.R.C.P., as an Honorary Phy- Honorary physician tO I ne JS.mg sician to His Majesty, vice Air Commodore Hardy Vesey THE Air Ministry announces that the King has Wells, C.B.E., M.R.C.S., L.R.C.P., who has vacated the approved of the appointment of Air Commodore Alfred appointment on retirement from the Royal Air Force. 251
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