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Aviation History
1934
1934 - 0101.PDF
FLIGHT, FEBRUARY 1, 1934 THREE NEW POBJOY ENGINES 90 h.p.. 80 h.p. and 70 h.p. \OR the 1934 flying season Pobjoy Airmotors, Ltd., ofH Hooton, Wirral, Cheshire, have introduced three new types of aero engine, all of which are now inproduction. The three types will be known as the" Niagara," the " Cataract " and the " Cascade " respec-tively, and are all 7-cylinder radial air-cooled engines, withmany components in com- mon, but differing in ratedpower. Two of the engines, the " Niagara " and the" Cataract," are geared, while the " Cascade " is ofthe direct-drive type. The difference in power betweenthe " Niagara " and the " Cataract " is due to thedifference in normal speed, the " Niagara " developing anormal power of 84 b.h.p. at 3,200 r.p.m., and the " Cata-ract " 75 b.h.p. at 2,906 r.p.m. The maximum powersare 90 b.h.p. at 3,500 r.p.m. and 80 b.h.p. at 3,200 r.p.m.respectively. The direct-drive engine develops a normalpower of 65 b.h.p. at 2,600 r.p.m and a maximum of70 b.h.p. at 2.850 r.p.m. The respective weights are 145 lb.,135 lb. and 126 lb., exclusive of exhaust collectors andcowling. As in previous Pobjoy en-gines, the weight-power ratios of the three new en-gines are low. Based on maximum power they are:1.61, 1.71 and 1.80 lb./h.p. respectively. All three engines have thesame bore and stroke, the swept volume being 2,835 c.c.(173 cu. in.). The maximum horsepower per litre capacity is 31.75 b.h.p., 28.22 b.h,The lower figure for the " the relatively low speed of ACCESSIBILITY : The 90-h.p. " Niagara " with bonnet raised, showing how accessible are the valvesand magnetos. Two rocker caps have been removed for inspection of rockers, etc. p. and 24.7 b.h.p. respectively.Cascade " is, of course, due to the direct-drive engine.Speaking generally, one may say that the " Niagara "is a new engine, totally en- closed valve gear, and a cowlsupplied as part of its stan- dard equipment being butsome of the features. The " Cataract " generally re-sembles the 1933 " R " type engine, but has a re-designed ignition system, im- proved cylinders, reductiongear and exhaust collectors. It is cheaper than the" Niagara." The " Cascade " is interest-ing in being the first direct- drive Pobjoy engine. Itgenerally resembles the " Cataract," but by the sacri-fice of about 10 b.h.p. this engine can be sold at a some-what lower price than the " Cataract." THE 90-H.P. NIAGARA ENGINE Tlic unusual structural features ofthe engine comprise the following :— The Cowling.—This consists of asubstantial chromium-plated * nose- piece supported on a tubular ringstayed rigidly from the crankcase. The rear edge of this nose-piece isthreaded with leather thong to provide a non-rattling support for the bonnet.Between the cylinders are provided deflector plates supported from flatplates anchored to the tubular ring. The tops of the finned cylinderheads are covered in by cast helmets, made detachable purely for manufac-turing convenience. The gaps between the front of the helmets and thecowling ring are bridged by sheet metal extensions screwed to theheads and lined with felt to prevent rattle. All the air entering the nose-piece is thus forced to circulate over the cylinder heads or around thebarrels. The passages are so shaped that airspeeds are recorded in them THE 90-H.P. "NIAGARA": The exhaust system can be seen in the photograph on the left, while in theright-hand view the engine is shown on a dummy mounting, with bonnet in position. .H£^:.:-:-.::^:;;^.:^~^>. 101 '-. • - -Z^.
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