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Aviation History
1947
1947 - 0388.PDF
FLIGHT MARCH 2OTH, 1947 AIRBORNE POWER STATION as well as emergency services and emergency lighting. The Shetland's generating plant, which was housed in a separate compartment with the main distribution panels, comprised two self-contained units, earn driven by a petrol engine rated at 60 h.p, at 12,000ft, and as each unit was capable of supplying all the electrical power required, this provided a 100 per cent stand-by. Each engine was direct coupled to its 3-phase A/C. alternator running at 3,750 r.p.m. and was geared to a combined D.C. generator and exciter running at 4,600 r.p.m. Speed was kept constant by a centrifugal governor, and the voltage, both A.C. and D.C., was maintained to within plus or minus 3 per cent by carbon pile.regulators. Wiring was essentially simple. From the main distribu- Thermal Heating Devices for Both A METHOD of applying thermal de-icing to airscrew bladeshas recently been announced by Hamilton Standard Pro- pellers. Two variants of the basic system are available, onefor hollow steel blades and the other for solid duralumin. In the case of hollow steel blades heater wires of special alloyare cemented to the inside surface of the blade leading edge. For duralumin blades, however, the heating element consistsof three laminations of special rubber mounted externally over the leading edge. The central layer is of conductive rubberwhich, by its electrical resistance, supplies the heat; the inner layer has good cementing and thermal insulation character-istics ; whilst the outer layer is of smooth finish and has a high resistance to erosion. The total thickness of the laminatedshoe is o.iin. In both the hollow steel and the duralumin blade installa-tions, the heated section of the blade extends for approxi- mately 75 per cent of the blade length and 20 per cent of thechord. Electric current is derived from the aircraft battery and isconveyed to the blades through the conventional slip-ring and brush system. Power supply is controlled by a timing devicewhich directs current to each airscew in turn, thus relieving the battery from constant full load. For icings conditions atmoderate temperatures a heat supply to each airscrew for 20- second intervals divided by 60-second shut-off periods hasbeen found adequate. But to cope with icing at very low temperatures [no indication of actual temperature is given— tion boxes (which had hand-operated isolating switches and thermal-operated overload trips) a number of feeders ran out to load centres in the aircraft where sub-distribu- tion boxes, housing fuses, and contactors fed the indi- vidual circuits. Duplicate feeders were provided for essen- tial services and an automatic change-over was arranged to switch the load from one auxiliary set to the other, and from a normal to an emergency feeder in the event of a fault. The actual wiring was so arranged that a section of cable between any two points could be readily replaced without disturbing the units to which it was connected. All terminals and conduits were lettered and numbered, while junction and distribution boxes had lid diagrams to facilitate the tracing of any individual circuit. Another valuable provision was a fixed earth indicator on the engineer's panel giving, at a glance, the total insu- lation resistance of the A.C. circuits to earth, so that incipient faults could be located. • De-icing Hollow and Solid Blades Ed.] a double-throw switch permits the selection of an alter-native cycle of 6o-seconds operation and 180-seconds shut-off. The timing device can be adjusted to meet varying timingrequirements on particular routes. In announcing this development it was stated that expert-ence and research have both shown that the removal of ice after it has formed is easier than attempting to prevent itsformation. By applying heat to the blade leading edges, the adhesion of ice is rendered impossible and the formation isthrown off by centrifugal force. The new thermal system is to become standard equipment on all Martin 202s and 203s,and on all Hamilton Standard-equipped Douglas DC-6S and Consolidated Vultee 240s. It will thus be used by -13 ofAmerica's 16 major airline companies. WESTLAND APPOINTMENTSW ESTLAND AIRCRAFT, LTD., who recently announcedthat the Sikorsky S-51 is to be built at Yeovil, have appointed Mr. O. L. L. Fitzwilliams, B.A., helicopter engineer.He has long previous experience with the Cierva Autogiro Co., and for a time worked under Mr. Raoul Hafner. Since 1944Mr. Fitzwilliams has been in charge of. the Rotary Wing Air- craft Section of the Airborne Forces Experimental Establish-ment at Beaulieu, where Sikorsky R-4B and R-6A helicopters have been undergoing trials. Mr. A. E. Bristow, who has beenappointed helicopter pilot, was in charge of the Helicopter Unit Air Base, Portland. Put Out We thank the many observant readers who wrote or telephoned, either to register disapproval of our caption, or to congratulateRolls-Royce " scene shifters ", after examining the before and after photos accompanying the article Universal Power Plants in our February 13th issue. Above we submit photographs of fire test No. 12 at Hucknall, to which the original caption applies verywell. In explanation we add that the earlier unmatched illustrations we« selected from a large number for their quality as photographs for reproduction.
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