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Show New Automatic Direction Finding Device Determines Position of Airplane in Flight By WILLIAM KELLER (Released by Western Newspaper Union.) CHICAGO. The danger of commercial aircraft becoming becom-ing lost because of inclement weather or faulty navigation has been practically eliminated elimi-nated by a revolutionary new invention. Location of a plane in flight is automatically recorded re-corded at ground stations by an automatic direction finding find-ing radio receiver developed by technicians under J. P. Cunningham, United Air Lines' director of communications. communi-cations. Four years of study and experimentation were conducted con-ducted under Cunningham and Sandretto, head of the company's radio laboratory, before the direction finder reached its present stage of perfection. A amazing degree of accuracy has been obtained by the device. Cunningham reports that tests conducted con-ducted over a period of more than a year reveal that better than 99 per cent of the bearings made by the new receiver proved to be accurate. Entirely automatic, the receiver operates without any special assistance assist-ance from the plane in flight. It is described as remarkably simple in operation. Each time that a plane in flight makes its routine half-hour position reports, the receiver acts on the radio waves. Large antenna that form the heart of the instrument pick up these waves. This antenna is constantly being rotated by a motor. Electric waves picked up by the antenna are transferred to a standard stand-ard radio receiver which amplifies it into energy. This energy operates oper-ates a moving pen which draws a line on a scroll chart that constantly unrolls beneath it. The pen traces the form of the wave in a vertical zigzag line which reveals the maximum maxi-mum and minimum strength of the signal. All bearings are based upon the minimum signal, or "null," as it is called by radio engineers. The null Is recorded when the revolving antenna an-tenna is exactly at right angles to the direction from which the signal is coming. The null as shown on the chart form can be plotted exactly from a transparent plexiglas plate graduated graduat-ed in degrees which is placed over the chart The radio operator can then read off the bearing of the airplane air-plane In degrees. It is necessary for at least two stations equipped with the antenna and recorder to work together In triangulating a plane's position. This position is then immediately radioed radi-oed to the pilot who uses the report re-port to check upon his own navigation. naviga-tion. If three stations take bearings simultaneously si-multaneously from a plane In flight, lines from the stations arc projected project-ed on a map. The exact position of the plane will be shown by the point on the map where the lines intersect. "In practice." Cunningham explained, ex-plained, "we will use two or more ground stations simultaneously in receiving re-ceiving the reports from any given airplane. The bearings obtained by these stations will be electrically transmitted to our key dispatching posts on the transcontinental route. There the bearings can be plotted on charts In a few seconds and we thus know the location of every plane within a mile or two. "For practical purposes, with a f&y-j i- A I R WAV " Operation of the new airplane location recorder is illustrated by this sketch. Ground stations equipped with the device automatically receive bearings on a plane every time its radio transmitter is used. By taking simultaneous bearings, stations A or B, which are on the airway, can determine the plane's position with the help of C or D which are off the airway. At the lower left is shown the revolving antenna which makes the high degree of accuracy possible. swiftly moving object like an ziiA plane, this is 100 per cent accuracy." Cunningham added that the first station is now being installed at Salt Lake City. United Airlines expects ex-pects to install about 20 to serve its entire system from coast to coast. Finding directions by radio is not a new science. It was known in 1912 when radio was still in its infancy in-fancy and was used at sea during the World war of 1914-1918. Pan-American Pan-American Airways engineers subsequently subse-quently developed a long range direction di-rection finding receiver. This receiver re-ceiver gave fairly satisfactory results re-sults over water where radio signals are more effective than land. Unsatisfactory results were obtained ob-tained about 1935 when the Pan-American Pan-American system was tried out over land. Since then an antenna system that would operate over land has been sought by a number of radio manufacturers, the army and the navy. Accurate results up to 80 per cent of the time were attained by a number num-ber of systems, but this was not considered sufficiently safe for use with passenger carrying planes. Static interference was the fundamental funda-mental cause of trouble with most of these direction finding receivers. It spoils signals and gives inaccurate inaccu-rate nulls. Because United's device produces visual charts it is possible to weed out the bad bearings. The army and navy are deeply Interested in the receiver. It has been offered to other airlines ir, the United States. |