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Aviation History
1958
1958 - 0437.PDF
FLIGHT, 4 April 1958 ; ' ••.,.,-. ^ CHASING THE ICE GREMLIN . . . even more important, it was not as turbulent as the type of cloudwe had had to fight our way through during our previous searches for dry ice. During our sorties in the Entebbe area we hadworked out a standard cloud-flying procedure, and this was closely followed on the Singapore exercise. After we had chosen a cloud which appeared suitable—usuallythe frontal type which took the shape of a massive greyish- black wall of cloud—the aircraft was set up in the correct con-figuration for the test. Speed was adjusted to 200 kt indicated, and the "B" skin jets in the outboard engines were switched on.All engine-performance data was recorded before entering cloud so that on completion of the test we could establish whetheranything untoward had happened during the period in cloud. During the test the complement of the aircraft was divided intofour specialist groups. The first of these was the flight crew, consisting of the two pilots, flight engineer, navigator and radiooperator. The navigator had quite a job trying to keep our position accurately plotted while circling round inside the cloud, and itwas the responsibility of the radio operator to ensure that we kept clear of airways and control zones. The navigator also made gooduse of the search radar, and not only for avoiding any embedded storm-centres: he was also able to use it to keep us within thecloud, as it gave a pretty accurate indication of the relative moisture concentration. Over Uganda in 1955, navigation in cloud by searchradar had been made considerably easier by the greater number of embedded storm-centres which could be used as landmarks. Theaccompanying photographs of the radar screen and cloud map are typical of those prepared on the sorties we made at that time.The principal duty of the meteorologists was to keep a constant check on the actual water concentrations through which we wereflying. The electronics group was responsible for recording the behaviour of one of the inboard engines to establish exactly whathappened during a "bump" (or "auto-relight"), which was quite a frequent occurrence on the unmodified engines in heavymoisture-concentrations. Such quantities as the compressor speed and pressure, jet-pipe temperature and whether or not the r.p.m.-drop had been sufficient to cause an auto-relight were all traced on recording tapes against a time basis. In the cabin of the aircraft was an automatic observer panelwhich enabled a team of flight observers to keep a constant check on the behaviour of all flight and engine instruments, togetherwith other instruments installed specifically for the tests on which we were engaged. An automatic camera was also set up to takephotographs of the panel at one-minute intervals. One of the flight observers was positioned beside me in thejump seat throughout the test and it was his duty to pass back information over the intercom to a writer in the cabin of theaircraft. Our height and airspeed and the outside air temperature were called out every minute, and other information such as thesize of any bump (measured in r.p.m. drop), which engine it affected and whether or not the ice detectors had come on wereall passed back to the writer, whose record was most useful in making a rapid assessment before proceeding with the next test.Once in cloud we usually flew into the centre—indicated by the maximum oxometer reading—and then flew either in circles or onreciprocal courses. Although we were airborne for as much as six hours at a lime, an hour at a stretch in cloud was about the mostwe could manage as a rule, for the degree of concentration required (Right) Annotated version of a typical cloud-map prepared from radar and other data. (Upper left) Photograph of the search-radar screen taken at point A on the map, flying due west, (20- mile display—the main storm cones are between 75 am! 20 miles away.) (Lower left) Search-radar photograph taken at point B, flying on a heading of 750 deg. (60-mile display —main storm cones be- tween 20 and 30 miles.) 453 of all taking part became fairly exhausting. For this reason wedivided our airborne time each day into three or four separate sorties into cloud. On leaving cloud we descended into wanner air (about+ 15 deg C) to get rid of any remaining ice accretion in preparation for the next sortie. The recording was kept going for about fifteenminutes after coming out into clear air because it was found that, owing to the change in precipitation, small bumps would stillcontinue to occur in the unmodified engines after we had been in cloud for a long period. December 6 and 7 were spent changing an engine which hadbeen damaged by ice. The following two days were devoted to more cloud flying, but towards the end of the afternoon on thesecond day No. 3 engine was slightly damaged by ice and we returned to base. December 12, our last day in Singapore, wasused for final engine calibrations with the "B" skin jets switched on and off. We left Singapore at 2345 G.M.T. on Friday the thirteenth.Fortunately I'm not superstitious; but we certainly hit some pretty foul weather, with headwinds of up to 100 knots at times. Touch-down at Filton was made shortly after seven o'clock next evening. From the pilot's point of view, the results obtained from "Singa-pore One" were remarkably encouraging. It was found that although the "B" skin jets were not effective in conditions of dryice alone, they were very nearly 100 per cent successful in the mixed ice conditions for which they were designed. It was there-- fore necessary to formulate a simple drill for the operation of the anti-icing equipment, namely that the jets should be switched onwhen in cloud at observed air temperatures between 0 deg C and + 12 deg C. At all other times after leaving cloud they shouldbe switched off. An important point to bear in mind is that the observed, or indicated, air temperature is, under cloud-flyingconditions, about 8 deg C above the outside air temperature. We made a two-hour test flight in cloud to test the drill andfound that whereas the two monitor engines registered 111 bumps of 100 r.p.m. or over, only one occurred in the engines using airjets according to the drill. On the same flight the monitor engines registered 19 auto-relights. None was registered on the modifiedengines. As a direct result of the tests the mixed-ice limitation has now been removed from the Britannia's flight manual. PRECIPITATION SurSR COSLBD WATSJR * FKSSVNT IN fiua 4UAMTITICS. | — ACTIVE CORSS (OaCATIHfi) C APPROX LIMIT O* VI«lBt-« CLOUDAT AIRCRAFT IWI0HT. CLOUD MAP. FLIGHT 123. SORTIE C CaMCTKUCTCD USING MARCH RAOAR ANO TOTAL WATSM. COMTKMT MtTtK . 28 NOV 1955 I3.OOHRSGM.T OVER SOUTH END OF LAKE TANGANYIKA . ALTITUDE : aSOOO TO 2S.5OO FT. RAM AIK TtMPtRKTUAl :"5 T»-B *C. ICK CRYSTAL PROCIPtTATtOM. KMUSIKI AIRFKAMI ICIN« HCH • IO NAUTICAL MIL«S .
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