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Aviation History
1944
1944 - 0610.PDF
3T4 F L I G H 1 ^APf.n ^3Bb. 1044 NAPIER SABRE I drive upper and lower pairs of straight-tooth pinions, and the airscrew-shaft gear is meshed with all four helical pinions. To equalise the drive from each crankshaft to its pair of reduc tion gears, a balancing device is provided. Each reduction gear is permitted a limited axial float and they are held up to their work by a balance beam pivoted centrally on a forked pillar anchored in the nose casing. Movement is damped by spring- loaded plungers on the ends of the beam, yoked to light tubular shafts mounted on two double- duty ball races in the hollow compound reduction gear. The nose casing carries the main ball thrust bewaring and the outer roller bearing for the airscrew shaft. ' Auxiliary components arc- arranged accessibly in compact groups on the upper and lower face of the crankcase. In each case the drive is by a longitudin ally arranged tubular shaft driv ing through an idler gear from the forward end of the crankshaft. Above the engine the components are in the main arranged transversely, and thus the drive is taken from the tubu lar auxiliary shaft by bevel gears.' Starting from the tor- ward end is the Pesco vacuum pump on the left and the i%M$ The sleeve actuation gear » mounted on the underside of the cylinder block The driving gear for fuel, oil and coolant pumps is assembled as a unit in the lower casing cover. Viewing the unit from the nose, the accessibility of the cylinder heads, sparking plugs and also the auxiliaries is strikingly apparent. airscrew control unit on the right. Next is the servo control unit which advances and retards the point of ignition in relation to the speed of the airscrew. Then come a pair of B.T.H. distributors running at half crankshaft speed, each of which has two concentric rings of 12 seg ments. The dual ignition system is divided into four groups controlled by four switches each isolating six cylinders. Due to the phasing of the two crankshafts, two cylinders fire simultaneously; thus for the complete unit there are six impulses per revolution. Upper and lower banks of 12 cylin ders are numbered on the left 1 to 6 from rear to front and, on the right, 7 t# 12 from front to rear The firing order, referring to the upper 12 cylinders, is 1, 9, 5, 12, 3, 8, 6, 10, 2, 7, 4, n. For the lower 12 cylinders, the consecutive order, of course, is the same but phased 180 deg. of crankshaft rotation in relation to the upper 12 cylinders. In other words, 1 (upper) and 6 (lower) fire simultaneously, fohowed bv 9 (upper) and 10 (lower), then 5 (upper) ar^** 2 (lower), and so on. Combustion Starter Next to the distributor is a pair of B.T.H". duplex magnetos running at 1.5 times crank shaft speed. The last bevel-driven unit is the Hey wood air compressor, but from the end of the tubular shaft is a train of spur gears from which three longitudinally arranged compo nents are driven. These are the 500-watt, 24-volt electric generator on the left and the supercharger lubrication pump and the Dowty hydraulic services pump on the right. Between the generator and the pumps is mounted the Coffman combustion-type starter. This unit operates through a dog clutch to the train of gears extending from the rear of the upper crankshaft to the hand-cranking gear. The starter has a five-cartridge magazine and is \ hd electrically. When the starter is operated, or when the engine fires, an automatic device
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