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Aviation History
1951
1951 - 0633.PDF
6 April 1951 393 RAIN-TRAINER Qantas DC-3 Equipped for Combined Rainfall-research and Crew-training VAST tracts of land in Australia could be transformedfrom useless waste into productive areas if there weresufficient water. It is not surprising, therefore, that the Commonwealth has shown active interest in the investiga- tion of cloud formations and in rain-making experiments. In many countries there are those who believe that in the not-too-distant future it will be possible to regulate rainfall to some extent; but before there can be any certainty of success an immense amount of research has still to be done. In Australia, the Commonwealth Scientific and Industrial Research Organization, under the leadership of Dr. E. G. Brown, has a radiophysics division which has devoted a good deal of time to such work. Its present programme provides for extensive research into the physics of clouds and of natural rain formation. By making possible the measurement of the magnitude of rainstorms and the examination of the composition of a cloud, micro-wave radar, a war-time development, has provided the meteorologist with a most valuable new instrument. Appropriate radar equipment carried in an aircraft—and this, of course, is where Qantas Empire Airways fit into the picture—makes it possible to seek out the rain-clouds and fly round, over and through them in order to measure and observe at first hand the type of precipitation, whether snow- flakes, ice crystals or water drops. Analysis of this informa- tion, supplemented by data on turbulence, is expected to Ocplain the mechanisms involved in natural rainfall.f In August of last year, C.S.I.R.O. discussed with Qantas the possibility of chartering a DC-3 aircraft for airborne radiophysical investigations. (Previously the work had been carried out with the aid of the R.A.A.F.) Some ten to fifteen flying hours per week were foreseen, and a scheme was worked out whereby part-time crew-training could be worked in with the investigation flights. A standard pas- senger-type DC-3 was selected, and some 3,000 lb of equip- ment was installed (see illustration). The aircraft itself was modified by the installation of a large-capacity oxygen sys- tem for high-altitude work and—to provide additional elec- tric power for the research equipment—200-amp generators in place of the normal 50-amp type of the DC-3. Research equipment includes SCR.717B iocm-wavelength radar, the antenna for which is mounted in a radome on the nose of the aircraft. As the antenna revolves in a plane at right-angles to the line of flight the position and magnitude of echoes reflected from objects such as the ground or a rainstorm are presented to the observer in the usual manner The principal interior andexterior special equipment installed in the Qantas DC-3. A—Radome containing antenna unit.B—Auxiliary instrument panel. C—Astrodome.D—Auxiliary BC-II53-A indicator. E—Capillary-collector panel.F—SCR.7I7B radar equipment. G—Aerial psychrometer. H—Cloud-water-content measuring instruments. I—Position of "dry-ice" chute. J—Inverter unit and soundproof box. K—Cloud-water-content pick-up. L—Oxygen bottles. on the cathode-ray tube. The aircraft itself appears as a spot on the centre of the screen, the ground-echo is visible at the bottom, and any echo from a rainstorm appears between the two. A second cathode-ray tube in the recorder permits accurate measurement of the intensity of the echo received from the storm. A camera and timing equipment secure a continuous record for subsequent analysis. The various well-defined types of rainstorms produce characteristic echoes. For instance, heavy rain observed to fall from cumuliform clouds lying wholly below freezing level have a column-like shape and an intensity which is relatively uniform from the top right down to the ground (see illus- tration). The mechanism of natural rain formation thought to be involved in such a case is that some of the cloud drop- lets grow first by condensation then more rapidly by coales- cence with other water drops. There is reason to believe that this process also takes place in some of the larger clouds which extend above freezing level. Another characteristic type of echo (also illustrated here) is that produced by strati- form cloud in which, according to theory, ice crystals form in the sub-freezing region, fall down through the cloud, growing in the process, and melting at a point just below freezing level to emerge finally as rain. An intensified echo is received from the layer—known as the melting point— just below the freezing level (this phenomenon is sometimes referred to as "Bergeron rain," after the scientist who pro- pounded the theory). A sideline to these investigations is the information pro- vided on aircraft icing. When an aircraft is flying above (Left) Radar echo from heavy rain from clouds below freezing-level. (Right) Echo from ice-crystals falling through cloud, melting, and forming rain. Aircraft at 11.000 n, 16- o c 1 +8'C 2, Echo from Ground ... .*/. ^, ,, j, . * ^ V.<-.. \~ ^^_^ „
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