The Arens System of Controls New Device now being Widely Adopted Jar Aircraft Use
FOR many years it has been generally recognised by aircraft engineers that there was room for improvement in the control systems of aircraft, and in the past decade methods have been devised and employed towards the perfection of this vital part of an aeroplane, so that durability might be increased, and more positive action effected. And to an appreciable extent this has been successfully carried out by the use of ball-bearings, the elimination of fairleads and the reduction in the
the reduction in the number of pulleys which, until a few years ago, were common features on all aircraft. A further step in the improvement of controls is found in the Arens system which has come into considerable prominence lately, mainly on account of Captain Barnard’s long distance flight on a machine fitted with
this system. Like other efficient and new devices, the Arens control is extremely simple. In main esseritials it comprises three parts ; an outer casing or tube of duralumin into which is inserted a tightly wound spring which is free to slide in this outer casing, and again, within this second component is an ordinary flexible cable. To each end of this cable is attached, by solder.ing, a forked-end rod, and these rods bear tightly against the spring member so as to fully compress it. One of these end rods (the one which is connected to the operating medium i.e., ” stick,” rudder-bar or lever), is extended and works plunger-fashion in the extremity of the outer casing so as to act as a guide to convey the ” push ” movement by the spring component. The pull ” movement is, of course, taken through the :inner flexible cable. The advantages offered by the Arens system at once become clear, for with it there is no necessity for pulleys, fulcrums, rods, or fairleads of any description since the outer duralumin casing acts as a .guide for the whole assembly. Moreover, there is no objection to the unit being bent round quite acute radii, tile minimum being in the smaller sizes, 11, inches
and in the larger, 4 inches. Another good feature is that there is no possibility of the controls fouling or becoming chafed by extraneous parts, and as it is packed internally with grease, it is practically without friction, and wear is negligible.
Some idea of the excellent wearing qualities found in this new system is provided in the figures given by the R.A.E., following some experiments some time ago. A length of Arens control was subjected to a test frictional re against a frictional resistance of approximately + or — 6 lbs., with engine oil as a lubricant. After 500,000 cycles the ” push “. member was carefully examined and it was found that the wear on the diameter was .01 inches and after a further 536,00 cycles, during which time the mechanism was sprinkled with
quartz sand, there was only another .015 inches of wear. The report also States that no strands were broken following this very strenuous test.
The Engineering Division of the United States Air Service has also put the Arens control to extensive trials with similar satisfactory results. Their official report was as follows :—speed on test, 128 cycles per minute ; duration of test 343 hours ; total number of strokes. 2,634,240 ; lateral slack at finish of test .015 inches and longitudinal slack at finish .005 inches.
The system is being widely adopted in the U.S.A. and it has already been accepted by the British Air Ministry for engine and secondary controls on aircraft, and by the German Air Inspection Department for use on German civil and military machines. For engine and, in fact, all remote controls it obviously has great advantages over the more usual rod system in that there is no possibility of waste action developing, and at the same time it is much simpler to adopt and fit.
Captain Barnard’s Puss Moth is the first machine to be installed throughout w th this device, but it seems likely that it will be widely adopted before very long.