FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1935
1935 - 1443.PDF
JUNE 13, 1935. FLIGHT. 649 cyurioeR PISTON 8ARREI 8LA0E ESUSHtlSC BARREL BOLTS CAP o PI0ER MlCARTA .__ RING COUNTERWEIGH SHAFT SHIM PLATE GUNTERWEIGH^ BRACKET Above are seen the components of an airscrew hub. The names of the parts are given in the illustration. Balancing a blade: A cylindrical rod rolling on knife edges forms the support, and the blade is balanced against a calibrated weight, as shown on the right. (Flight photograph.) cold water and immersed in nitric acid. This is washed off in a bath of boiling water and the blades are then examined for minute cracks. If no defect of any kind has come to light the blades are balanced against a gradu ated master weight, which represents, so to speak, a standard blade. The balancing is done by supporting the blade and master weight on a cylindrical steel rod which rests on knife edges. To illustrate the care necessary in getting the balance exactly right, it may be mentioned that each airscrew, complete with its hub and C.P. mechanism, of course, is first assembled and balanced dry. Grease is then forced into the hub under great pressure, and the airscrew is balanced once again. If the grease has penetrated properly to every corner in each blade the balance should, of course, still be perfect. If, for any reason, it has penetrated farther in one blade root than in another the fact will show on final balancing. The work on the parts of the hub has to be equally meticulous. As previously mentioned, the forgings for hub barrel and spider are obtained from outside. The two halves of the hub barrel are forgings by the English Steel Corporation, in D.T.D. S82, while the spider, in D.T.D. S81 steel, is supplied by Firth Derihon. The sub sequent work on the steel parts of the hub is mainly plain straightforward machining, and does not call for any special comment. It will be realised that the loads are very heavy, and that if the slightest play were allowed during assembly the least amount of extension and deflection while running would result in play developing, and this, in turn, might give rise to flutter and cracking. It is understood that the "Gipsy Six" controllable- pitch airscrews now being manufactured at Stag Lane will probably be put on a D.H.86 to be tested out in actual flight. In the meantime one of these airscrews is being sent to the Hamilton works in America to be tested out on a special machine which introduces artificially vibrations of a magnitude far greater than would ever occur on any actual engine. This machine brings to light any faults in design much more rapidly than would operation on an engine in flight or on the test bed, and information is thus made available quickly after the introduction of each new design. Incidentally, it is of interest to learn that calculations indicate that the cruising speed of the D.H.86 should be very materially increased by the fitting of C.P. airscrews. This, of course, is due to the fact that the engines will then be run at full throttle, the speed being kept down to cruising revs by the setting of the airscrew blades. Mention was made earlier in these notes of the fact that controllable-pitch airscrews for the Bristol '' Pegasus '' and "Gipsy Six " engines are already being manufactured in considerable numbers. These are by no means the only models, and preparations are being ma3e for making air screws for all the " Bristol " models, for the de Havilland Gipsy Major,'' as well as for all the Rolls-Royce aero engine types. In the case of the Armstrong-Siddeley aero engines controllable-pitch airscrews will be manufactured for all the higher-powered models (the smaller scarcely re quiring them), while plans are in hand for C.P. airscrews suitable for the Napier series of engines. It will thus be seen that it should not be long before these airscrews are available for fitting to any suitable British engine. At present it is not possible to give exact figures of weight and price. As a very rough guide it may, how ever, be taken that the extra weight of a controllable-pitch airscrew is somewhere in the neighbourhood of one-half pound per horse-power. This figure does not cover the en tire range, being lower for the lower powers. As regards cost, it is again difficult to quote figures, but something in the region of £2 per pound weight will not be wildly wrong. Final assembly. The airscrew is first assembled dry. it is then balanced and grease is forced into the hub under great pressure. A final balance then ensures thai the grease has penetrated everywhere. Flight photograph.)
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
