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Aviation History
1936
1936 - 0273.PDF
JANUARY 30, 1936. FLIGHT. 121 While the position of <the trunk air routes in this country remains, to some extent, in doubt, the use of easily moved D/F stations is an advantage. This is the interior of one of the Marconi mobile units. airport quickly lays the bearings out on a chart. The point of intersection cf the lines gives the machine's posi tion at the moment when the bear ings were obtained. Direction-finding equipment can also be carried by the machine itself, either as a " homing " device—in which case the pilot turns until an instrument tells him that he is flying directly towards any selected radio station—or as a radio compass, by which a pilot may take a direct bear ing on any radio station while flying on his original course. Such equip ment is of particular value in parts of the world where there are no ground D/F stations within calling distance. Another form of navigational aid is the visual or aural radio beacon. The words " visual and " aural " may possibly confuse the uninitiated, since the words apply only to the method" of indication as far as the pilot is concerned. The beacon signals tell the pilot whether or not he is flying directly along a previously arranged line of transmission. Such beacons are widely used on American air lines, but in Europe's complicated air-line system, where it is necessary in bad weather for a control officer to keep track of all the different machines in the air, the ground D/F system is considered to be at least temporarily superior. Supplementary Beacons In due course this system will suffer from the effects of overcrowding, and supplementary automatic approach beacons are already installed at a large number of Conti nental airports, and examples will soon be ready for use at five British airports. European methods have crystal lised into a form of " zone " traffic control, in which a control officer at a terminal airport is responsible for the safety of all machines within a certain radius. In bad weather there are small controlled zones around certain airports into which no pilot may fly without first obtain ing permission. Again, in due course it may be necessary in the interests of safety to develop a " layer " system for bad weather, whereby each pilot will be given definite height limits between which he must fly. As already mentioned, the necessity for some system by which pilots can approach and land at an airport when the visibility is virtually zero has hurried research in the matter of short-wave characteristics. The first method to be used, however, for blind approaches in Germany and elsewhere depended entirely on the delivery of con tinuous bearings by normal means ; on the ability of the pilot to fly an accurate course on his blind-flying instru ments ; and on the accurate aural sensibilities of the con trol officer. A rough-and-ready method of this kind demands an exceptionally long landing run, such as can only be found at a few airports, in addition to at least one clear approach. In America the present standardised blind approach system involves the use of a special radio beacon and of two marker beacons (transmitting upwards) at carefully arranged distances from the airport and on the line of approach. By means of a homing receiver the pilot obtains a line on the airport and adjusts his directional gyro ; on his approach he uses the marker beacon signals and a previously re-set sensitive altimeter while flying on a memorised series of flying and engine speeds to provide the correct approach angle after crossing the outer marker beacon at a predetermined height. While making h's landing actually blind he must fly very gently on to the ground. The now well-known Lorenz system was developed in Germany and is to be used expsrimentally at Heston in the very near future. In this system, which involves the use of wavelengths of the order cf 8 to 10 metres, accurate directional guidance is automatically given in both the horizontal and the vertical plare from a station at the far end of the landing run, while two marker beacons, laid out on the approach track, tell the pilot his exact distance from the airport boundary. Briefly the main beacon projects two beams, slightly overlapping in plan view, one signalling in " dashes " and the other in " dots." On the line of overlap a continuous dash is received. These signals can be heard in the pilot's earphones and are, at the same time, used to actuate an instrument on the dashboard which functions more or less MARKER BEACON | MAIN i AERODROME DASHES CONTINUOUS NOTE mmmmm^m^m ©eSSe*"-?"-*- 3ft ./<> These purely diagrammatical sketches show how the Lorenz blind landing beams are projected. The sketch on the right shows how the signals merge into a continuous note along the approach line. As at present arranged at Continental airports the main beacon marks two courses at 180 deg. to one another.
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