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Aviation History
1950
1950 - 0569.PDF
FLIGHT, 23 March 1950 Discernible at the rotor tips in this recent view of the Top Sergeant are the pulsejet units, now highly developed. TOP SERGEANT rr REJOICING in the sobriquet Top Sergeant, the littlepulsejet helicopter shown here is a product of theAmerican Helicopter Company, of Manhattan Beach, California, and is the outcome of a U.S.A.F. re- search and development contract. For this class of machine the makers consider that the payload for a one- hour flight should be double that of a piston-engined heli- copter of the same gross weight. Production cost is esti- mated at a quarter of that of the lowest priced commercial helicopter available to-day, and the maintenance and over- haul costs of the pulsejet power units should, in turn, be a quarter of those for a conventional engine. Many problems connected with the pulsejet power units are said to have been eliminated under the U.S.A.F. con- tract. Early units failed under whirl loads of up to 200 g but no structural weakness is now apparent. The valve blocks (the only moving components), which initially had a relatively short life, now give promise of a life of 30 hr or more. Replacement of a worn block can be effected in The pulsejets compared with a piston engine for similar duties. 5 min and represents the only " major overhaul " required. It is stated that a new configuration recently evolved will substantially reduce the drag of the jet units (mounted at the rotor tips) and simplify autorotation problems. A spokesman for the manufacturers states that massive pulsejet helicopters, of '' flying crane'' form, would carry their power plants buried within the rotor structure, thereby presenting only minor drag problems. Studies indicate, however, that pulsejet size, and unit thrust, will not have to be increased for greater all-up weights; it will merely be necessary to increase the number of units per blade to achieve the required thrust. Components of the fuel-supply system of the Top Ser- geant are an electrically driven fuel pump, throttle, master shut-off valves, fuel flow gauge (" rotometer ") and a rotary fuel-line transfer seal—the latter purchased '' off the shelf" from an oil-well supply firm. The only highly loaded moving parts in the structure are the two rotor mounting bearings. Mr. Corwin D. Denny, president of the manufacturing concern, is reported as saying, " At times the absence of a welter of moving parts, whirling and bobbing up and down, amazes even us. It's like discovering a good 5-cent cigar! " The simple cdmjk>nents\which ensure* a\stfffj>)y » of fuel to thepulsejets. The gauge measures rate of flow.
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