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Aviation History
1935
1935 - 1442.PDF
648 FLIGHT. JUNE 13, 1935. (Left) Two blade forgings, one half of the hub barrel, and a spider. Above is seen the operation of grinding the blade down to exact shape. (Flight photographs.) HOW C.P. AIRSCREWS are MADE Interesting Processes in the Manufacture of the Hamilton Airscrew at Stag Lane : Working to Very Fine Limits RECENT articles and correspondence in Flight have concentrated attention on the subject of the variable-pitch airscrew, or, as it has more recently come to be called, the controllable-pitch airscrew, the latter expression being, perhaps, more descriptive. It may there fore be of interest to readers to learn something about how one type of C.P. airscrew is manufactured, so far the only- one to be in quantity production in this country. This is the De Havilland C.P. airscrew, manufactured under licence from the Hamilton Standard Company of America. As most readers of Flight will be aware, the De Havil land Aircraft Co., Ltd., transferred to new works at Hat field some months ago, but the old works at Stag Lane have been retained, and the De Havilland aero engines are still being manufactured there. A portion of the old aircraft works, the erection shops, has been turned over to the production of controllable-pitch airscrews, and an Reamering the inside of the hollow blade root. The next operation is smoothing the bore with another tool. The airscrew blade is held in a cradle on a long lathe. (Flight photograph.) extensive plant of machine tools, etc., has been installed. Production has begun, and C.P. airscrews for the Bristol " Pegasus " engines and for the De Havilland " Gipsy Six " are now coming along fairly fast. All the machining operations on the airscrew parts are being carried out at Stag Lane, but blades, hub barrels, spiders, and so forth, which are forgings, are obtained from outside. The blanks for the light alloy blades are supplied by High Duty Alloys, Ltd. Most of the machining operations on them are carried out by the De Havilland Company, but an exception is the shoulder on the blade root. This shoulder bears against one side of the roller bearing which takes the centrifugal pull on the blade, the flange on the hub barrel bearing against the other side. The work of forming this shoulder is done by Turton, Platts, and Co., the roller races having to be slipped on before the shoulder is formed, or before the up-ending process, as it is called. Thus the blade blank arrives at Stag Lane with the blade root already up-ended. The machining of the shoulder is, however, done in the De Havilland shops, a Broadbent lathe with a 15ft. bed and ao^in. centres being used for this and for boring the internal diameter of the hollow- blade root. The forging is held in a turning cradle and the boring has to be interrupted at intervals to clear out the swarf by compressed air. A machine is to be obtained shortly which, being vertical, will permit the swarf to fall out, and for other reasons as well will shorten the time taken to bore out a blade root. The work has to be very carefully done, two conical faces having to be machined to fit exactly the two tapers on the spider. When the shoulder and internal bore of the blade root have been finished the blade is transferred to a table on which the face is worked by hand, the small curvatures to be dealt with making this a fairly short operation. The blade is then turned over and the cambered side worked down to contour, first by a milling cutter and after wards by an electrically driven grinder. Gauges for front and back of the airscrew blade at stations spaced 6in. apart are used, the opposing gauges meeting on leading and trail ing edges. After shaping, the blades are rough polished and then transferred to a bath of hydrochloric acid, rinsed in
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