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Aviation History
1939
1939 - 0085.PDF
JANUARY 12, 1939 FLIGHT A Dagger VIII complete with spinner, nose cowl and chutes for the cooling air. DAGGER VII Details of a 2^-cylinder H-type Engine Now in Large-scale Production 1,000 h.p. at 8,750/Z. ; Major Improvements AN increase in power of something like 200 h.p. and a rise in rated height have resulted from improvements *• incorporated in the Napier-Halford Dagger VIII engine, now in large-scale production at the Napier works at Acton. This new unit, like its predecessors, is characterised by the arrangement of twenty-four small air- cooled cylinders in the form of an H ; high operational speed and compression ratio ; small frontal area ; and high output from a comparatively small cylinder capacity. Under maxi mum power conditions for level flight the output is no less than 59 h.p. per litre. The Air Ministry describes the new engine as having an "intermediate-altitude" supercharger, which means that the rated height is rather greater than that of current medium-supercharged engines but not so high as for the new fully supercharged models. The maximum output of 1,000 h.p. is actu ally attained at 8,750ft., the rated out put being 925 h.p. at 9,000ft. Apart from a variety of minor changes in layout and construction the Dagger VIII exhibits a number of major improvements in comparison with its predecessor, the Dagger III. These include an increase in fin area, a double-entry supercharger, and pro vision for a constant-speed airscrew. The general arrangement of this unconventional type of engine will be apparent from the cut-away drawing on the two following pages. The aluminium alloy crankcase is in two halves, joined along the horizontal centre line. Spigot-mounted to the front and rear end respectively are the nose-piece (which houses the main re duction gears and the drives for the magnetos, distributors and control unit for the constant-speed airscrew) and the timing casing. Each pair of cylinder blocks—port and starboard—has one crankshaft; these are machined from [Continued after double-page drawing The double-entry blower is the most promi nent feature at the rear of the new Napier.
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