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Aviation History
1950
1950 - 1502.PDF
172 FLIGHT, 10 August 1950 RESEARCH INTO RUBBER . . . vibrated on a movable test-plate, whatever the position of the plate the supported weight remained unaffected. Rubber undergoes a marked change in mechanical properties over the temperature range between 20 deg C and —65 deg C. From the universally known resilient material with small permanent set at room temperatures, it passes through a stage of increased permanent set as the temperature is lowered, until it reaches a final stage where it is very hard and tough—like wood or Bakelite—and of very low flexibility. In this state, when sufficient force is applied, the material will fracture in a brittle manner. Understandably, this property is of considerable importance in the design of rubber components for aircraft which operate at high altitudes or in polar regions. An apparatus used at the Research Centre for testing tyres under low- temperature conditions consists of two parts, (i) an indus- trial-type refrigerator with an 8 cu ft capacity cold chamber, capable of attaining any temperature down to —65 deg C, and (ii) a self-contained tyre-impacting device, which can be lowered on to the refrigerator, so that the tyre is inside the cold chamber. The impacting unit is pneumatically operated, with automatic pre-set load-limiting devices, so that it can simulate the force and timing of the initial land- ing impact of an aircraft. Tyre load and deflection are recorded on a chart, and can be arranged to illustrate the complete cycle as a hysteresis diagram. The recent development in silicone rubbers has had a very considerable effect on the applicability of rubbers and rubber-like polymers at extremes of temperature. The heat-resisting properties of the silicones were those first to attract attention, and these properties are remarkable. For example, as part of the normal preparation of silicone articles, they are heated from 4 to 24 hours at 250 deg C, a temperature at which all organic rubbers would either harden up to a bone-like state or decompose to a sticky mass. After a preliminary run of some months on a pilot plant, Dunlop have now set up a new unit at their works in Cambridge Street, Manchester, for turning out products in Here shown on removal from its cold soaking, the tyre is seento be covered with frost, and the rubber is hard and brittle. silicone rubber. Although the silicone rubbers are pro- duced in various grades of hardness and mechanical properties, all possess the outstanding characteristic of retaining rubber-like properties under conditions of extreme heat and cold. They will, in fact, give an economical life from —55 deg C to 210 deg C. Sealing rings, vibration dampers, and hot-air ducts are but three examples of aeronautical items which will be produced in these materials. To complement the English centre, and to work in co- operation with it, Dunlop Malayan Estates have recently opened a rubber research centre near Batang Malaka, Negri Sembilan, the primary purpose being to adjust the supply of latex to the varied demands of industry. A LIGHT-AIRCRAFT ODYSSEY THE news of Rhodesian developments on pages 175-177lends topical interest to a noteworthy light-aircraftflight from Africa to England, recently accomplished by Mr. and Mrs. C. H. Perrem (of Umtali, Southern Rhodesia), both of whom are in their fifties. In 96 hours of flying, spread over 15 days, their Auster Autocrat (Cirrus Minor II) covered 8,500 miles from Umtali to its makers' airfield at Rearsby. Some months of preparation preceded the journey, which followed the rarely used route via the Belgian Congo, Cameroons, Gold Coast, Rio de Oro and Gibraltar. The Perrems started from Umtali at first light on June 17th, and touched- down at Rearsby on July 2nd. After thirteen years of active flying in Africa, including a journey from Umtali to Heston and back in 1938 in a Heinkel H.E.64D, with a Gipsy III engine, the couple were under no illusions that the new trip via the West Coast would be easy. The stage from Umtali to Elizabethville was flown over some heavy bush, particularly north of the Zambesi to Ndolo. Elizabethville-Kamina-Luluaborg proved to be an easy stretch along the railway, but Luluaborg to Leopoldville lies over dense forest and featureless country, and was covered in thick haze that limited visibility to about five miles. From Leopoldville to Point Noire, as the railway could not be followed through the mountains and forest, a westerly course was set to follow the lines of the mountains until the Atlantic Ocean was sighted, and a turn was made to port to follow the beach to Point Noire. From there to Libreville Mr. Perrem found to be the most interesting part of the jour- ney, the route lying over very heavy forest, frequently broken by grass clearings occupied by large numbers of wild animals. " We flew this section at 400 feet in what we think was safety," Mr. Perrem told us, "and got a good sight of the wild life." From Libreville to Duala brought the Auster into the bad- weather area under the influence of the I3,ooo-ioot Mount Cameroon, and during the last 100 miles to Duala the weather deteriorated to such an extent that it was forced to skim the tops of the trees; eventually a chance flash of a tin roof gave a line for Duala. " From Duala southwards around Mount Cameroon was a nightmare," said Mr. Perrem, "and we had to fly far out to sea around the bad-weather area on the west side of the mountain. Coming clear of the fog and rain, we found our- selves out of sight of land, but, managing to make a landfall near the mouth of the Niger, we landed at Port Marcourt. Great care is required on this section as bad weather and difficult locations of towns increase the difficulties. Port Mar- court to Abijan was a delightful run along the line of the beach. Abijan to Freetown is over heavy jungle, and we met much cu-nim cloud. We went above it, but maintained V.F.R. conditions. "The Freetown to Dakar section involves navigation over extensive watering systems. Dakar to Vila Asneros, and on to Agadir, is as bad as driving a car the wrong way up a one- way street, the airflow being from north to south 25 knots to 40 knots over several months of the year. On this section our windscreen became affected by some deposit which gave the effect of frosted glass, and try as we could, we could not remove it. '' The last stretch to Agadir was flown under a 100-foot ceiling over the sea adjoining the cliffs of up to about 150ft. This was most unpleasant, and my wife had to lean out as far as possible and direct me to fly close enough to the cliffs to maintain visual contact. This bad weather was with us on arrival at Agadir, and our difficulty was to transfer ourselves from the low ceiling over the sea to the low land where the airfield was situated. We found a river running inland and followed it, to make a landing in better flying conditions. Agadir to London was enjoyable and average." Great praise was due to the Auster and its Cirrus engine, said Mr. Perrem, for a faultless performance during the entire flight.
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