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Aviation History
1953
1953 - 0113.PDF
BELL MODEL 54 • Externally, this machine, which bears the U.S.A.F. designation XH-15, resembles a scaled-down Model 48 (YH-12). It is, however, a two-seater and is intended primarily for observation, liaison and communication work. The absolute ceiling is in the region of 20,000ft, and the top speed over 100 m.p.h. The two-blade rotor, which has a diameter of 37ft 4m, is driven by a Continental O-470-5. engine of 275 h,p. Gross weight is approximately 2,800 lb. DOMAN YH-31 AND LZ-5 • These machines are products of Doman Helicopters, Inc., of the Municipal Airport, Danbury, Connecticut. Both are descended from the LZ-4, a research heli copter which was purchased by the Curtiss-Wright Corporation and is still being test-flown. The YH-31 is the military medical- evacuation variant of the LZ-5 and the general description applies to both. Inclination of the tip-path plane of the four-blade rotor relative to the fuselage is accomplished by gimbal-mounting the rotor hub and rotating it with a constant-velocity driving system. Thus, no blade-flapping hinges, drag hinges or hinge dampers are required, and the bearings subject to centrifugal loads with oscillat ing motion are reduced to a minimum. The rotor retains dynamic balance in all flight attitudes, with consequent decrease in vibra tion, and the makers point out that though there are certain other Gyrodyne G.C.A.-2C. rotor systems employing a gimbal mounting, these are subject to a condition of dynamic unbalance. The reduction gear is incor porated as an integral part of the rotor assembly. All moving pans are contained in a common housing which precludes contamination, and circulating oil is pumped to all bearing surfaces, thus reducing the frequency of servicing. Although the Doman helicopters appear quite conventional they do, in fact, embody a number of features which are not commonly met with. Thus, the engine is mounted low in the nose of the fuselage, with the crankshaft inclined upwards at an angle of 32 deg. There is a fluid drive with a mechanical pick-up on the engine crankshaft flange, coupled with a tubular drive shaft having universal joints. The tail rotor is driven from a gear in the main rotor assembly at an r.p.m. ratio of 2.09:1. Above the power plant section, from which the engine can be rapidly removed without recourse to hoisting equipment, is the cabin, to the rear of which is stowage for baggage. The rotor blades are interchangeable and each has a spar built up of plastic bonded birch laminations, with a plastic bonded mahogany plywood covering. A "utility" version of the LZ-5 or YH-31, with uncovered fuselage structure, winching arrangements, etc., is offered for applications where maximum payload is desired. Suggested appli cations include agricultural dusting and seeding, ship-to-shore cargo shuttle, wire-laying, extra-high-altitude operation and timber patrol. The models so far mentioned are normally powered by the 400 h.p. Lycoming SO-580-D, but the makers have recently announced a twin-engine development, obtainable either by purchase of a new helicopter in that configuration, or by the con version of one of the single-engined types. Power will be supplied by dual 200 h.p. gas turbines which, being of very light weight, will allow the aircraft to carry 2,140 lb of useful load at speeds up to 98 m.p.h. At present the Doman company is encouraging operators to use the single-engined machine with a view either to conversion, or operating a mixed fleet of single- and twin-engined types. The following data apply to the LZ-5: rotor diam., 48ft; empty weight, 2,860 lb; gross weight, 5,000 lb; max. speed, 98 m.p.h.; cruising speed, 86 m.p.h.; hovering ceiling (no ground effect), 4,000ft; hovering ceiling (in ground effect), 8,000ft; permissible e.g. travel, ioin; fuel capacity, 100 gal. GYRODYNE G.C.A. 2C • Of unusual technical interest, in having co-axial rotors, this product of the Gyrodyne Company of America, Inc., Flowerfield, St. James, Long Island, New York, is powered with a Pratt and Whitney R-985 engine of 450 h.p. and is a 5/6-seater. The rotors are of the semi-rigid type and incor porate automatic locks which prevent flapping at low rotor speeds and permit operation in high winds. In the transmission system there are only five gears. Although the company has hopes of an order for the G.C.A. 2C it pins its faith to the convertiplane. An earlier version of the G.C.A. 2C (G.C.A. 2A) was adapted to take two 85 h.p. Conti nental engines on outriggers and thus to provide data for the convertiplane programme. Directional tests in the "one-engine out" case proved quite satisfactory. The following figures apply to the G.C.A. 2C as now flying: rotor diam., 48ft; empty weight, 3,800 lb; gross weight, 5,400 lb; disc loading, 2.98 lb/sq ft; max. speed, no m.p.h.; hovering ceiling^(without ground cushion), 5,900ft; vertical rate of climb, 625 ft/min. Jacobs 104.
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