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Aviation History
1944
1944 - 2380.PDF
534 FLIGHT NOVEMBER I6TH, 1944 Modern Airscrews—III Descriptive Review of de Havilland Hydromatic By C. B. BAILEY*WATSON DOME HUB SHELL. INNER CAM \OUTER CAM, PISTOI OIL FRO/ C.S.0 ENGINE AIRSCREW SHAFT ROLLERS' DISTRIBUTOR VALVE ASSEMBLY FRONT CONE HUB SUPPORT BLOCK _OIL TUBE (ENGINE) THE heart of the Hydromatic airscrew, as, indeed, of other de Havilland and Hamilton models, is a com ponent called a spider, mounted on the airscrew shaft of the engine and consisting of a splined hub carry ing three radial " spokes " on which the forged duralumin airscrew blades are mounted. The spider is drawn up on annular cone seatings at each end of the splined bore, and the static and thrust loads are focused and taken upon these, the splines merely transmitting torque. Each blade has a hollow shank and is mounted upon its appropriate spider arm with a micarta sleeve or bush to take the journal loads, and, in additibn, to absorb some of the shaft / blade vibration. Centrifugal loading of the blade is taken by a single-row needle-roller thrust bearing housed in two machined collars which are en- THE first article in this series ('•Flight," November 2nd, 1944) dealt with the advantages of variable pitch and de scribed the Rotol hydraulic airscrew. This was followed last week by a description of the Rotol electrically operated airscrew. The present article explains the features of the de Havilland Hydromatic, a name compounded to signify that it is hydraulically operated and automatic in action. Illustration of sectionalised Hydromatic hub. The several components assembled together can be identified in their rela tive positions, and the pitch-change actuation can be followed. closed between the radius of the blade root and the tip of the blade port in the hub shell. On the root of each blade is fitted a bevel gear segment through which pitch change motion is transmitted from the driving gear of the pitch- change mechanism housed in a dome carried on the front of the hub. The hub shell is in two parts, being divided in the plane of rotation of the airscrew, with the halves secured together by means of twelve bolts. Internal support for the hub and accurate concentricity and alignment with the spider is provided by three micarta support blocks. This exploded view of the Hydromatic hub shows the relationship and unit shape of the various components. These can be identi fied with their location by reference to the heading illustration.
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