FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1922
1922 - 0163.PDF
MARCH 16, 1922 THE LOTH GUIDE CABLE An Interesting French Aid to Air Navigation ALTHOUGH there were relatively few things upon which members of the recent Air Conference agreed, it was inevi table that in all that mass of problems there should be some upon which every one was agreed. Among these was the desirability of being able, to fly by night and in fogs. Vir tually the ability to do this amounts to doubling the speed of any given aeroplane—at any rate, qver long distances. Even for such short routes as the LoWon-Paris, it was pointed out by several, notably by Gen. Williamson of the G.P.O., that a night air mail service would be valuable and would save a great deal of time. In addition to the advan tages of being able to save time by flying at night, the ques tion of reliability and regularity of service is closely bound up with the capability of flying in fog or clouds. With modern instruments the problem of flying in clouds is perhaps less serious than that of carrying on during foggy weather. Nevertheless, pilots do not particularly like flying in or over clouds—at any rate, until the wireless service has been so far developed that a pilot may at any time, and with a minimum of delay, obtain his bearings by D.W. Progress is being made in many directions, and there is little doubt that before long fogs, clouds and darkness will have lost much of their danger to aircraft. Among the various inven tions which have for their object the making safe of flying under such conditions, not the least interesting is the guide cable adapted for aircraft by M. Arthur William Loth, a French engineer. Experiments along similar lines have been made at Portsmouth and in New York, using a cable for directing ships during foggy weather. The problems con fronting aircraft are, however, somewhat different, notably vertical panel, 2 the lateral horizontal panel and 3 the lateral vertical panel. These panels are connected to a telephone receiver, as in ordinary direction-finding wireless, via a commutator, so that the navigator can " listen in " on either of the three panels. According to the position of the machine in relation to the cable, the intensity in each of the three panels varies or may even disappear. For instance, when the machine is flying parallel to the cable, the sound is a maximum in the longi tudinal panel 1, and nil in the transverse vertical panel 3. As the machine diverges from the course parallel to the cable, the sound diminishes in the longitudinal panel, and increases in the lateral vertical panel, in which the sound becomes maximum when the machine is at right angles to the cable. The sound in the longitudinal panel then vanishes. The horizontal panel has the property that the sound in it vanishes when the machine is vertically above the cable. It will thus'be seen that if an aerodrome has a cable running around it, the navigator of a machine can determine, even in a thick fog, the exact moment of crossing the cable, and by finding the height from the altimeter he can determine at what angle to glide into the aerodrome in order to make a landing. A special commutator enables the operator to put any two of the panels in series, and the information gained by so doing enables the exact position of the machine in relation to the cable to be determined. Thus, by placing in series On the left, installation on board the aeroplane for utilising the Loth Guide Cable : 1, longitudinal panel ; 2, horizontal panel ; and 3, transverse vertical panel. On the right, lines showing magnetic field produced in space by the cable. on account of the third dimension in which an aircraft moves. While it cannot, perhaps, be claimed that M. Loth invented the guide cable, he can, at least, claim the credit of having adapted it for use with aircraft, and the Loth system is, in our opinion, one which is likely to prove of the greatest use in the future. The following notes on the Loth guide cable are based on an article by M. P. James in our excellent French contemporary /'Adrophile. The fundamental principle of the Loth guide cable rests on the fact that if a high-frequency alternating current is sent through a cable earthed at each end, a magnetic field of considerable intensity is created around the cable. The effects of this field can be detected by means of suitable instruments at considerable distances from the cable. Thus if an aeroplane or airship is equipped with these instruments, its navigator can determine his position relative to the cable, and thus ascertain his bearings. Although the principles are very simple, M. Loth was faced with numerous problems before bringing his system to perfection. Thus he had to do a tremendous amount of research and experimental work in connection with the formation and extent of the magnetic field surrounding the cable. This work took a long time, as measurements were often taken at intervals of a metre or so. The lines of force, shown in the accompanying diagram, were found to vary with the frequency of the alternating current sent through the cable. The lines shown in the diagram represent the field resulting from using a frequency of 600 per second. As regards the equipment of the aeroplane, this is simple in principle, consisting in mounting in a suitable place—for instance, on the tail of the machine—three panels of insulated copper wire so placed as to be at right angles to each other. Thus in the accompanying diagram, 1 is the longitudinal the longitudinal and transverse vertical panels, the operator can determine whether the machine is inclined to right or left in relation to the cable. In order to determine whether the machine is approaching the cable from left to right, or from right to left, the longitudinal and horizontal panels are placed in series. Placing the transverse and the hori zontal panels in series serves to indicate the vertical distance above the cable ; in other words, it shows whether the cable is running up or down the side of a hill or mountain, or whether it is running horizontally over flat ground. By the use of the Loth cable, a machine can thus travel along over any sort of country, the navigator knowing his position, and knowing that he cannot accidentally run into a hill in the fog, as his receiver will warn him if he approaches too close to the cable. If this happens while the machine is flying horizontally, he knows that the cable is running up the side of a hill, and if he is on a familiar route he will probably know which is the hill in question. Put in another way, the guide cable is both a direction wireless and a contour map of the route flown. It goes without saying that the inventor had many diffi culties to surmount, difficulties not directly connected with his system, but which had a considerable effect on its develop ment. Thus* it was found that the magnetos caused such a noise in the receiver as to drown, or nearly so, the sound from the wireless panels. To overcome this difficulty, it was necessary to explore ^the magnetic fields of the magnetos thoroughly, and this was consequently done. We do not propose to tire our readers with a technical description of how M. Loth overcame the difficulties. Suffice it to state that he has succeeded in doing so. Not only so, but he has found means of interrupting the sound from the wireless panels for the very short interval occupied while the spark- 163
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
