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Aviation History
1937
1937 - 0162.PDF
-6o FLIGHT. JANUARY 21, 1937. by other lights and signs. In bad visibility a much more powerful beacon is required, and perhaps the best compromise will ' be a rotating beam with or without a red colour screen and a separate red identifica tion light. The power of the main light would be regulated according to the weather. Both in Germany and the U.S.A. the double-ended rotating route beacon is gaining favour owing to the greater length of flash. This allows the use of alternate white and red or other coloured flashes for identifica tion. A maximum beam candle power (white light) at 12,000,000 is in use. The power consumed bjr a route beacon of this type is not considerable unless it has to be generated specially. On long-distance and overseas routes greater ranges may come into use and a beacon near to, if not at, the aero drome, which in moderate visibility can be picked up eighty miles away will certainly have its protagonists. Having approached the aerodrome the more complicated the shape of the landing ground becomes, and the greater the number of zoned obstruc tions in its vicinity the more will the pilot need a really effective system of obstruction and boundary lighting, and perhaps special approach lighting in addition. New methods are alreadv being tried. In the well-known Phillips installation at Welschap Aero- The neon tube airport identification beacon by Clarke Chapman. A G.E.C. floodlight for Malaya. The housing, which contains a venti lating fan, is weather-, bird- and reptile-proof. The Chance flush-fitted marker light of the type referred to by the author. drome at Eindhoven, special threshold lights are placed at 80ft. spacing in addition to the usual obstruction and boundary lights and may be switched on independently to form a strongly lighted threshold to the appropriate runway. The most interesting feature of the threshold lights themselves is that they are of the high-pressure sodium discharge type such as are now used for street lighting at Croydon and elsewhere. This gives an intense and very pure yellow light which is not readily confused with any other. The low-pressure neon discharge tube has long been used in Germany for boundary markers, but the Dutch in stallation is one of the first steps in the use of the recently developed high- pressure discharge lamp, from which much is expected in the future. Threshold lights alone do not give the landing direction, and another system used in America, and recently installed by the Westinghouse Electric Co. at Basrah, makes use of gieen marker lights placed at the near and far ends of the runwaj . All the lights may be switched on, with the boundary lights, and the markers for each runway are dis tinguished by difference of number or grouping. This system depends for its success on good visibility and it may also fall short of what is wanted for landing out of wind. The system which in theory seems most attractive is the line of marked lights set flush in the surface of the runway itself. A number of such lights are in use throughout the world. They must project as little as possible and must be very robustly constructed. It is in consequence very diffi cult to get a satisfactory intensity of light at an angle less than 40 deg. from the horizontal. Since, when making a normal approach, they may be viewed from 5 deg. to 20 deg. above the horizontal, this is a grave drawback which still remains to be overcome. A Boundary'light " Horizon " Where landings are confined to surfaced runways use may be made of lights of the boundary marker type, which are designed to be easily knocked over without damage to aircraft. These lights may be adapted to illuminate the surrounding ground surface and so help in the next prob lem—which is to enable the pilot to touch down on the surface of the landing ground. Given reasonably level ground, many pilots find the horizon provided by the boundary lights of the utmost value for this purpose. It is consequently most important that these should have a good intensity in the horizontal plane and stand sufficientlv high above the ground. It seems to be admitted universally that for a normal "all ways" grass-covered aerodrome, the floodlight gives to a pilot without much experience of night flying the best chance of making a good landing. The intensity and number of floodlights used is consequently increasing.
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