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Aviation History
1923
1923 - 0782.PDF
DECEMBER "27. LEADER CABLE SYSTEMS FOR STEERING OF AEROPLANES ALTHOUGH tests have now been proceeding in France for acouple of years or more on the " Leader Cable " invented by M. William Loth, comparatively little has become known inthis country concerning the working and principle of this invention. In FLIGHT of March 16, 1922, we published a shortarticle dealing with the Loth guide cable, giving such few- particulars as were available at the time. Beyond that,however, little or nothing has been published in English relating to this interesting subject, and it was, therefore, witha good deal of anticipation that we visited the Royal Society of Arts, where, on December 14, M. Loth's paper on his leader THE LOTH GUIDE CABLE : This photograph showsthe receiver installation on an aircraft. cable was read before the Institution of Aeronautical En-gineers by Mr. John Gray, B.Sc, M.I.E.E., as the writer of the paper, although understanding English perfectly, does notspeak it sufficiently well to be able to give a lecture. Mr. F. R. Simms was in the chair, and the lecture was very wellattended. Owing to the fact that the paper, as written by M. Lothwas a very long one, and that Mr. Gray could only deal with portions of it in the time available, we do not propose to givea rdsumS of the paper itself, nor an exact report of the short lecture delivered by Mr. Gray. Rather do we intend, in thefollowing notes, to attempt to offer a brief explanation of the principles involved and the apparatus used, without neces-sarily following the sequence and method of either the author of the paper or of Mr. Gray. The original translation of thepaper, and the lantern slides used, have been very kindly placed at our disposal by M. Loth and Mr. Gray, "with, ofcourse, the consent of the Institution of Aeronautical Engineers, and i£, therefore, in the following notes anyinaccuracies should be found, or any glaring omissions of important points, we alone must be held responsible. Briefly, the Loth guide cable for aeroplanes is not new inprinciple, but the old idea of using a cable emitting electric current for guiding ships into harbour has been applied byM. Loth to the guiding of aircraft. M. Loth has been working on this subject for something like ten years, and quite earlyin his researches he became convinced that before he could hope to solve the problem it would be necessary to explorethoroughly the magnetic field surrounding such a cable. This he consequently set to work to do, and when it is stated thatthe magnetic field has been explored up to distances of 15 kilometres (9 -3 miles) from the cable it will be realisedthat the task was a formidable one. However, M. Loth persevered, encouraged by the French aviation authorities, and notably by M. Laurent Eynac, Under-Secretary of Statefor Air, who placed machines and pilots at the disposal of the inventor. The experiments and mathematical studies of theshape of the magnetic field disclosed the fact that the field is not a simple magnetic field, but a resultant field formed bythree elementary magnetic fields. These are : (1) the field due to the current flowing in the cable (this is the least importantfor guiding purposes) ; (2) the magnetic field due to the return current in the ground or sea ; (3) field due to the currentsinduced in the conducting mass surrounding the circuit. The basic principle of the guide cabfe is shown diagram-matically in Fig. 1. At a station situated at one end of the guide cable used is an electric alternator producing anoscillating current of a certain frequency in the primary circuit. The secondary circuit consists of the guide cable(which can be placed either on poles above the ground or buried in the ground), the ends of which are led to earth platesand the return current passing through the earth. The station end of this cable has a secondary coil placed near the coil ofthe primary circuit. When, therefore, the alternator is working, the alternating current in the primary circuit inducesan alternating current in the secondary circuit—i.e.. in the guide cable. For work over the sea the cable is laid on thebottom, as indicated in the diagram Fig. 2. The alternating current in the cable and eartii circuitproduces a magnetic field, and if the aircraft to be guided is provided with suitable apparatus the variable magnetic fieldcan be detected. For instance, ear phones may be employed, when a certain note, varying with the frequency of the circuit,will be heard. It has already been mentioned that the magnetic field surrounding a guide cable is not a simple one.Experiments have indicated that it is somewhat of the shape shown in Fig 3, and that, therefore, according ro wherein this magnetic field the detecting apparatus is placed, it will be differently affected. The small crosses seen in. Fig. 3represent the coils of the receiving apparatus, mounted on the aircraft to be guided. Reference to these coils will be madelater. For the present it may be stated that, fundamentally, the receiving apparatus consists of three separate coils, onelongitudinal vertical coil, one transverse vertical coil, and one 782 Photograph showing a portion of the guide cable surrounding the Villacoublay aerodrome. horizontal coil. According to the position of the receivingapparatus in the magnetic field one of these coils will be more affected than the other two, and will thus give an indication ofthe relative position of the aircraft. As the guide cable, running across country, will not be in a straight line, but will
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