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Aviation History
1953
1953 - 0121.PDF
FLIGHT, 23 January 1953 119 LEONIDES AND BOMBARDIER Key Features of Two Standard British Helicopter Power Units COOLING FAN SHROUD EXHAUST COLLECTOR /STARBOARD\ \ SIDE / HEAT EXCHANGER ENGINE STARTER DETECTOR SWITCH WHEN the Alvis company began development of the Leonides engine before the outbreak of war in 1939 they could hardly have foreseen its eventual importance or the range of applications in which it would enjoy a virtual monopoly throughout much of the world. The fact that the Leonides holds so strong a position today is not due just to a lack of competition, but rests largely upon the engine's own excellence. All types of Leonides are notable for their small dimensions and short piston-stroke; for a useful, low-pressure fuel-injection system, which permits single-lever engine control; the complete enclosure of all lubrication and valve systems; and protection against radio interference and ic;ng. From the opera tional point of view, the Leonides is unusually adaptable, for it can be fitted with almost any type of accessory; can drive several types of airscrew or rotor, either directly or through gearing; and is fully cleared for operation in tropical or cold-weather conditions. As a power unit suitable for helicopters, the Leonides is un surpassed by any other engine available, either in this country or abroad. Most British Leonides-powered rotorplanes employ one of the variants of the basic vertical-crankshaft engine specially developed for such applications. The engine itself, in such installations, is usually stripped of accessories as far as possible —a procedure which results in a power plant of very low overall height. From the crankshaft the drive is taken through a high speed cooling fan to a centrifugal clutch. This clutch—often Alvis Leonides Bristol-type engine as adapted for Bristol 171 and 173. Varies in exhaust collector rings and pick-up points only. a Borg and Beck unit—does not engage until the crankshaft speed has reached about 1,000 r.p.m., so allowing easy starting. The outer, or driven, member of the clutch is attached to the lower end of a drive-shaft which leads to the main gearbox just below the rotor. The gear ratio is typically about 12:1, and the secondary drive-shaft couples the gearbox to the anti-torque rotor or syn chronizing shaft. The accessories may also be mounted on the gearbox, where they are readily accessible, and continue to function during autorotative flight. In the majority of British helicopters the main drive gearing is by the E. N. V. Engineering Co. The two-row Leonides Major, which is expected shortly to make its first public appearance, seems assured of an equally useful future in both fixed- and rotary-wing fields. It has already been selected as the power unit for more than one new helicopter project and when it becomes available the Alvis company will be able to cater for helicopter requirements between 500 and about 900 b.h.p. Alvis Leonides 524/1.—Nine-cylinder, air-cooled radial, with poppet valves and fuel injection carburetter. Single-stage supercharger. Diameter, 4i£in; length, 32£in; dry weight, 642 lb. Maximum power, 525/545 b.h.p. at 3,200 r.p.m. with +7 lb/sq in boost at sea level. Alvis Leonides Major 1-2.—14-cylinder, two-row, air-cooled radial. Diameter, 39m; length, 48-55H1; dry weight, 960 lb. Maximum power, 870 b.h.p. at 3,000 r.p.m. with + 8 lb/sq in at sea level. THE BOMBARDIER Blackburn Cirrus Bombardier.—The Bombardier is unique in a number of ways, for although it is of only moderate size it embodies a number of features normally restricted to much larger engines. An inverted four-in-line unit, it makes use of an efficient fuel-injection system, with consequent gains in fuel consumption and freedom from rough running and icing. The valves are driven by an underhead camshaft, the ignition circuit is fully screened, and a very wide range of accessories can be fitted. I«s helicopter applications have so far been limited to the various types of Saunders-Roe Cierva Skeeter, which is now in production for a number of military roles. In the Skeeter the Bombardier is virtually the same engine as mounted in fixed- wing aircraft, but it is mounted transversely across the fuselage behind the cockpit. A belt-driven cooling fan is mounted on the starboard side of the aircraft at the "front" of the engine; the rotor is driven from a specially arranged gearbox and clutch. Blackburn Cirrus Bombardier 704.—Four-cylinder, inverted in-line, air-cooled, with fuel injection. Unsupercharged. Width, I7in; height, 3iin; length, 45|in; dry weight, 354 lb. Maximum power, 180 b.h.p. at 2,600 r.p.m. at sea level. The Bombardier installation in the Skeeter; the engine is supplied by Blackburn and General Aircraft, Ltd. as a bare unit with a splined drive-shaft, the rotor drive being added by Saunders-Roe, Ltd.
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