Radio broadcast .. (1922-30)

514 Radio Broadcast "The problem of night flying and of using radio to assist the Air Mail to cross the Continent in a day," he explained in the authorized interview following. " boils down to three major questions: (1) Which stages of the long trip shall be flown at night? (2) What kind of radio equipment shall be used on the planes and on the ground? (3) What types of field and between-field lighting shall be employed?" The third question, he says, is already settled: so-called gas accumulating searchlights, which operate automatically for months at a time without attention, have obvious advantages. Pointed skyward, placed conspicuously at the fields and at intervals of fifty miles or so between fields, such lights, both in point of effectiveness and simplicity, are the best answer to the least difficult of the three major problems. Which gaps between New York and San Francisco shall best be covered at night is a larger problem. It may be, Mr. Edgerton explains, because of the enormous demandnotably by banks — for the swiftest possible service between New York and Chicago, that the entire run of 753 miles between these cities will be covered, eventually, at night. Yet this great distance includes the New York to Bellefonte, Pa., run, the worst run of all heretofore, mainly because of its fogs and mountains. Certainly, he adds, the Reno-San Francisco gap, to cover which a pilot must fly higher than in crossing the Alps, is out of the question both as a matter of safety and of Post Office strategy in expediting the mails across the continent. But the remaining question, concerning radio equipment, will be to most of us the most interesting aspect of the Air Mail's ambitious plan. Here the problem is twofold. One phase of it has to do with supplying means by which the pilot, high up, clipping the welkin in the middle of the night, can keep in continuous touch with ground stations, and possibly with amateurs now and then. The other phase has to do with providing what Mr. Edgerton calls navigation aids — radio direction finders and radio field localizers. "These things," Mr. Edgerton believes, "are possible of accomplishment. Ideally, the pilot simply wears a special radio telephone helmet, designed to exclude motor noise. On his plane a coil of wire is wound — about the struts for instance — and is connected to a receiving set on board. Then, as when a direction finder is mounted on a ship, and is oriented, the signals from a given transmitting station, or radio beacon, are loudest when the coil is pointed directly at the station. Moreover, if such a coil is mounted rigidly on a plane so that it points in the same direction as the plane, it can readily be seen that if the pilot pivots the plane so as to keep a maximum signal in his ears, he is bound to fly, as on an imaginary line, straight toward the beacon. Then, flying high, he can evade or fly through fog, his worst enemy, instead of having to fly low where he must dodge physical obstacles. But if the beacon is at the point of destination, the pilot will still be unable to locate the field exactly in thick weather because there is apparently a blind spot around each regular transmitting station, or beacon, which increases in size with the length of waves used. On a clear night, if he is careful not to level out to land too soon, and if the field is properly lighted, he can usually land all right. But if the night is not clear he will lose his direction, experiments show, just when he needs it most. " It was to help him land that the radio field localizer was developed in 1918 and 1919 with the assistance of the Bureau of Standards radio section and the Navy. Various designs were tried out. One consisted of an insulated wire laid on the ground round the edges of the field, charged with low-frequency current and intended to operate like an audio cable such as the Ambrose Light cable, perfected by the Navy. But the device that we expect to use — experiments to develop which were begun at the Bureau of Standards in August, 1918, and then carried on at our former field at College Park, Maryland — is a peculiar kind of radio transmission aerial which transmits vertically in the form of a cone that gains diameter with increased altitude. At a height of about 3,000 feet above the field such a cone can, we believe, be made to have a diameter of nearly a mile. Distinguishing between the direction finding and landing signals, and spiraling down inside this theoretical cone, the pilot can, as he ap . proaches the field, approximate its centre and his own altitude and effect a landing." Experiments to apply the principles of radio direction finding to postal airplanes were begun, in cooperation with the Navy, in February, 1919. At that time a direction finder was