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Aviation History
1968
1968 - 0237.PDF
WHT International. 15 February 1968 coverage, but not so small that they will be lost. In some voes of work, a fine mist or aerosol is desirable, which will • tentionally be permitted to drift. Such a cloud of chemical n -penetrate foliage, drifting among the leaves without ia-acting on them. These mists are usually produced by the I iection of a suitable oil-based chemical direct into the Iriiaust system of the aircraft engine, where it is broken up Into particles. As the exhaust gases cool they become saturated, bd the oil and water vapour contained therein condense on hydroscopic nuclei present in the gas stream, and produce a rog Such a system has been developed by Agavenco Inc for he Bell 204 helicopter. In herbicide operations, coverage of the leaf area of crops j relatively unimportant, as the chemicals used act through the jplant's system, and a few droplets on each plant are all that fare required. But it is usually most important that the spray (should not drift, as it can be damaging to other crops. Here use of large droplets, perhaps 500 microns in diameter, Is indicated. To exclude as far as possible the small droplets, use is made 'hi "bifluid" systems, such as Shell Biflon, which produce invert emulsions of water in oil. The additional complication of such system is outweighed by the fact that it offers greater safety |n herbicide operations than do conventional nozzles. Other approaches to the same problem include the use of additives, such as hydroxyethyl cellulose, to increase the viscosity of spray liquid and prevent the formation of fine droplets when using [conventional nozzles. These and many other methods are being employed in the 231 attempt to raise the efficiency of aerial application, and to get the chemical to its target with minimum loss. But, as indicated, the tendency has been to develop a type of equipment in isolation, with little consideration of the aircraft to which it will be fitted. It is now getting on for 20 years since W. H. Reed produced his classic study of the theoretical behaviour of droplets in the wake of an aeroplane, but the advent of the integrated airborne spraying system seems little closer. One part of the system has made some progress lately—that of navigation. While flagmen are adequate for marking out individual fields for the pilot, there are serious difficulties in guiding aircraft across large areas of forest or bush country. The US Department of Agriculture has been obtaining encouraging results with the use of Decca Navigator in range- land spraying programmes, and a British operator, ADS Aerial, is reported to be planning to use Decca for its operations in Pakistan. Another British firm, Ripper Robots, has completed a considerable amount of work on electronic guidance systems, with the ultimate object of developing a pilotless aerial spraying machine. Meanwhile the bulk of aerial spraying continues with traditional methods. Obviously the cost of developing improved techniques is beyond the average aircraft operator, and will only be able to be borne by aircraft and chemical manufac- turers and by governments. The latter are unlikely to provide much financial support until they can be convinced of the role that aircraft can play in maintaining the world's food supplies. For the time being we will have to recognise the agricultural aircraft for what it is—a rather expensive form of farm tractor. DECISION GUIDANCE FOR V/STOL (continued frompage 224) directional beams by using aerial arrays do not arise. Operation at C-band frequencies implies, of course, line-of- ssight con-tact; situations may be envisaged where a dog-leg ath may be necessary to avoid obstructions or to comply with nunicjpal regulations. In such cases, an auxiliary, or relay, aerial may be necessary in order to keep in contact with the craft out to the required acquisition range. The ground equipment (Fig 3) which will be used in the ^forthcoming trials consists of the aerial, six phase comparators, i general-purpose digital computer and a data link, together nth kinetheodolite instrumentation for reconstructing the flight path for performance analysis. Flight-path commands will be I&played on ILS instruments in the aircraft and duplicate instruments will enable observers on the ground to monitor the transmitted commands. A plotting board and television (the camera for the latter being situated on the runway so that personnel in the building can observe the aircraft from the most advantageous position) complete the ground installation. The airborne equipment consists of a data-Hnk receiver, digital decoder, store and digital/analogue converter, a trans- mitter-receiver operating at 0.5W, and a suitable aerial. As stated above, no transponder is used; the ranging signal merely passes through the equipment and is retransmitted from a suitable beacon. While no particular effort has been made to package the equipment into the smallest possible size, all Hie necessary functions for an operational commercial or military system could probably be built into a 1 ATR case with a weight of well under 501b. A fully transportable, battery-operated system to give area coverage in tactical military situations could be carried out by Land-Rover see heading impression on page 222) and set up at very short notice. The need to provide facilities in such theatres may very well be the first application of this versatile system. systems 36 years ago Marconi AD.22B com- munications equipment in a Saro Windhover. It was installed van endurance record attempt in which the Hon Mrs Z th e and two other crew members hoped to keep ithT*'G'Psy^"e'med flying-boat airborne for a month " ^e°'d of aerial refuelling from two Bristol fighters. °* succeed> ^"ugh toy achieved 54hr I3min atTheythe
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