Radio Eye As Guide For Lost Flyers

Sun (Auckland), Volume III, Issue 671, 24 May 1929, Page 16

Radio Eye As Guide For Lost Flyers

Wireless Beams that Tell Airman Where He Is TRACK. THROUGH FOG rpHE outstanding lesson of the mishaps to the Southhern Cross and the Kookaburra is the necessity for providing wireless beacons and directionfinding radio to guide airplanes ovei the principal airways of Australia, says, the “Sydney Sun.” At best, the air is an unfriendly element, but the greatest hazards to which aviators are submitted are thick fog and low-hanging, deep cloud banks. Either alone is evil enough, but when the two are combined the pilot’s lot is not an enviable one. The presence of fog, without lowhanging clouds, enables the flyer to get well above it, and permits clear vision, so that such high elevations as mountain-tops may be avoided. But the pilot of today who lacks the radio eye can make only the wildest guesses at the nature of the country which lies beneath him, under the fog blanket. Where low-hanging clouds come down to meet the upper reaches of the fog blanket, and together expand from the earth’s surface to an altitude far beyond the flying reach of a loaded commercial airplane, some means of knowing what is hidden beneath, or in the visually impenetrable area, is invaluable to the pilot. Altitude Errors The ordinary barometric pressure altimeter is by no means perfect. Pressure variations are responsible for some of its vagaries. Apart from this, the altimeter is usually set at zero when the plane is on ground at the home airport. The airdrome may be at sea level, in which case the altimeter error will be slight, but it is very likely not to be at sea level, and every 100 feet of error, together with the inherent imperfections of the instrument, may easily be responsible for a fatal crash. An outstanding feature in the radio eye (or, more technically, the radio altimeter), which is now in process of development, is that it not only tells the aviator his height above the actual ground beneath him—-not above sealevel —but that it also discloses the character of the surface. What the Altimeter Tells

Briefly, its principle is that it is a “standing” wave, transmitted from the plane from a rigid horizontal antenna installed over the length of one wing, just behind the loading-edge. The wave is projected earthwards, and the projection of the wave, together with its reflection back to the receiver installed on the plane, and the difference in amplitude as measured at the transmitting and receiving sources, give a basis for calculating the height of the machine above ground. A study of the charactistic reactions of the radio altimeters reflected wave when passing over various types of country has been made and accurately recorded, so that the pilot who is

j familiar with the instrument can ; know what the fogs and clouds are I hiding from his eyes. ! When passing over bush country, the visual indicator vibrates and jiggles as the standing wave transmitted from the plane is reflected first from a tree-top, then from the ground in some small clearing, and back again from a tree as the plane sweeps over it. Onl3 r the incomparable speed of the electro magnetic wave makes this possible. Visible light of any brilliancy is worse than useless for night landing during a fog. A wing-tip flare, lighted in a fog, will give an impression to a pilot that his plane is about three feet off the ground, whereas he may be anything from 40 to 1000 feet up. It is here also that the radio altimeter, it is hoped, will eliminate one more of the pilot’s risks. Besides the radio eye, three other inventions promise to minimise the hazards of the air, and their application to Australian machines and Australian air routes would go far in the development of local aviation. All these have been proved efficient, and are in regular use in other parts of the world today. “Where Am I ?” One provides the fitting of an airplane with an ordinary transmitting and receiving wireless set. By means of this, the pilot signals to two ground stations, asking “Where am I?” Each of the ground stations must be equipped w-itli a special installation which can fix the direction from which the message comes. Use of Triangle Supposing the stations are A and B. As soon as A receives a message it knows the exact direction from which it comes and knows, therefore, that the airplane sending it out is somewhere along the straight line of the message. It does not, of course, know whether the machine is near or far—--10 miles distant or 100 miles distant. This is where the second station, B, can help. B also receives the same message of inquiry from the plane, and being equipped with directionfinding apparatus the same as A, knows the direction from which it comes. Thus it is possible to draw two lines, going out toward the plane from each station, and the point where both lines meet and cross must be the spot where the airplane is.

The two stations, by reporting to each other, are able to make this calculation and then radio back to the plane its exact position at the moment. The whole operation occupies about two minutes. This system was in operation for

cross-Channel flights beween Enel, and France as early as 1921, and used during the war. In one non case of fog, a plane flew from pj!' to London without the pilot seeirthe ground for more than a few m?, 1 utes during the whole trip. All t v way he was guided by wireless'. The second method is the fitting „< , direction-finding apparatus to a plat. ! and by this means the pilot nirlt, , any station-say 2KC-and | straight for it. His job is as simp: as steering a ship to a light. Direc;! ihe diverges from his course thapparatus shows him whether he T j swerving to the right or left. Th, j equipment weighs only about 70ft Of course, this method is useles, where there is no broadcasting staticat the proposed terminus of the Highalthough even then, if there is a l station sontew here near the objective it serves to set the pilot well on his way. The third method is the directional beam, and it served the Southern Cross well during its hop from San Frandst to Oahu —the first stage of the train. Pacific flight. Twin Beams The land, or "beacon,” station sends out twin beams of sound—in diagram form they look very like twin beam; of light from a lighthouse. On onbeam the sending-station transmits a continuous stream of A's, which in Morse are “dot-dash”; on the other a continuous stream of N’s “dash-dot. ’ The receiving set with which the airplane is equipped naturally picks up these signals as long as it flies along either beam, but as the bean broadens out avith the increasing distance, just as a ray of light would, it would be useless for an airman to rely upon a single beam of sound, which would be hundreds of miles across at a distance of 400 or more miles from the sending-station, j As the two beams are adjacent, there is a relatively narrow beam of sound where the A's and the N’s merge Into one sound, the dash-dot of the N and the dot-dash of the A becoming a single, prolonged dash—which is Morse for T. As long as the airplane keeps within the confines of the T beam, the sound is neutralised by the pilot's receiving set, and he know r s that all is well. Directly he sheers to one side, the call-letter of the beam to which he is veering sounds a warning "dashdot” (or “dot-dash” as the case may be) in his ears, and he swings the , plane over, until blissful silence I assures him that he is on the comparatively straight and narrow T path again.