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Aviation History
1949
1949 - 1545.PDF
FLIGHT, 8 September 1949 309 BRITAIN'S POWER UNITS Specification Digest of Current Turbojets, Turboprops, Reciprocating Engines and a Rocket Motor IT is our' custom at this time each year to summarizethe progress made with power units during the pre-ceding twelve months. The year 1949 has seen the gas turbine establish itself even more firmly as the pre- dominant aircraft power-source, and the eyes of the whole aeronautical world have been turned toward this country as the mainspring of information and experience. The first rush of new designs has now passed, and with six different basic types of turbojet and six of turboprop run- ning we have sufficient choice to meet all immediate tur- bine requirements. Pairs of turboprops, driving co-axial airscrews, are also finding favour. A great deal of time has been devoted to development with a view to increasing power ratings without sacrifice of reliability, to increasing life between overhauls and, par- ticularly in civil units, to reducing fuel consumption. In addition, installation, controls and anti-icing have received attention. Such has been the improvement in operational char- acteristics following many hundreds of hours of experience with various gas-turbine units (and, of course, in airframes to take them) that the date for introduction of turboprops and turbojets into service in passenger aircraft can be stated with reasonable accuracy. In general it may be said that gas turbines have proved remarkably reliable and have shown themselves to require the minimum of routine atten- tion. Complete changes of power plant have been made within an hour. For aumenting thrust in military turbojets, re-heat (afterburning) which has been studied for some years past, will this year be publicly demonstrated on two fighter types. Designers of military aircraft continue to call for greater thrust, and more than one completely new turbojet design is being prepared to meet their requirements. Advances in metallurgy axe playing, and will continue to play, an important part in gas-tnrbine developments, and much has still to be learned in the production field. For example, should the several advantages of using light-alloy blades for axial compressors be sacrificed to obtain those others—in particular, durability—bestowed by steel blades? Heavy demands continue to be made upon the airscrew designer, and during the year satisfactory, if not ideal, solutions to the fine-pitch control problems—starting and idling—associated with turboprops have been found. Piston engines, large and small, still have an important part to play, and a degree of refinement and automaticity previously undreamed of has been achieved in the few re- maining large commercial power plants. The lower- powered engines of recent conception have, like the gas turbines, been undergoing development, and they give promise of matching the dependability of their forerunners while showing a marked improvement in performance. There is still a gap in the range—to the disappointment of many light-aircraft pilots—due to the absence of any unit designed to give under 100 h.p. For the first time a British-designed-and-built rocket motor is exhibited publicly. Its primary use is to augment the take-off thrust of a jet airliner when operating from short runways. The absence of compounded power units, of very small gas turbines, and of variants of the conventional turbo- props and turbojets (such as ducted fan and so-called by- pass engines) should not be taken to indicate unawareness of or disinterest in them. Re-heat equipment and title first rocket motor are by no means entirely new, although their existence and use in this country was a confidential matter until a few weeks ago. Alvis LeonidesQ UITE recently Alvis Leonides engines added anotherexample of satisfactory service to the year's operations at home and abroad when as power units of the Percival Princethey took part in a rigorous proving flight round Africa. The nine-cylinder radial Leonides power plant exists in morethan one form, but the basic engine, recently type-tested at a higher rating of 550 b.h.p., is the same in each case. Thecapacity is 11.78 litres. When used in helicopters—Westland-Sikorsky and Bristol 171—the unit is modified to run in the horizontal position(crankshaft vertical), and a cooling fan and clutch are added. The Gyrodyne, however, takes the engine in the normal ver-tical position. No reduction gears are fitted to -the helicopter units except in the case of the Westland-Sikorsky when as aWasp Junior replacement the Leonides has a combined reverse and reduction gear. The Le.23.HM (short unit) is installed inthe latest Bristol 171. Data for the standard power plants Mk 15-18 are: — Max. w.m. cruising power at 2,600 T.p.m. and 11,750ft, 320 b.h.p.; take-offpower at sea level at 3,000 r.p.m., 550/670 b.b.p.; dry weight, 760/790 Ib. Alvis Leonides Leonides Helicopter Unit
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