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Aviation History
1944
1944 - 2259.PDF
NOVEMBER 2ND, 1944 MODERN AIRSCREWS —• ; ——: screw oil tubes. Inside the hollow gear shaft is the piston valve which has lands upon it and is moved by the centri fugal governor, so determining to which oil tube the high- pressure oil shall be fed. When the piston valve is in a central position both outlets are blanked-off by the lands, and the high-pressure oil from the pump is by-passed back through a relief valve to the suction side of the pump. Speed Control The centrifugal governor consists of two L-shaped fly weights, the lower arms of which bear against the outer race of a ball bearing mounted on the end of the piston valve. On the other side of the ball bearing is a flange against which bears a coil spring to compensate the centri fugal movement of the fly-weights. Above the spring is a sleeve along which are cut racking teeth to mesh with a toothed segment controlled from the pilot's cockpit. Thus, according to the position to which the segment is turned, the tension of the coil spring is either lessened or ^increased in order to balance the centrifugal moment of Ihe fly-weights and so determine the position of the piston valve and the consequent distribution of the oil to the airscrew oil tubes. Inside the racked sleeve a further coil spring is housed, the object of this being to ensure that the sleeve is kept in the position for normal cruising r.p.m. should the control from the cockpit be shot away or become disconnected. It will now be appreciated that the speed at which the engine runs is governed purely by the pitch of the airscrew blades, and that the pilot's throttle lever affects only the manifold boost pressure—it does not affect the engine r.p.m. But for the control which does affect the r.p.m. of the engine thereJs ipso facto an excellent case for drop ping the usual title of "pitch control lever" in favour of "Sons of Well-produced Film About the A. IT takes quite a long time to make a film, even a docu mentary, so it may reasonably be assumed that when it was decided to make " Sons of the Air," which tells the story of the Air Training Corps, neither Mr. Castleton Knight, ..the producer, nor Fit. Lt. Edward Jarratt, who supervised for the A.T.C., had any suspicion that by the time their finished product reached the public screen, the Government would have decided to whisk a very large proportion of A.T.C. cadets into the Army instead of the R.A.F. This is no place to discuss the inevitable disappointment— not to say discouragement—of thousands of A.T.C. cadets and potential cadets caused by what we must accept as a necessary decision, but it does mean that the general " recruit ing campaign" tone of the film struck me as a trifle incon gruous as I watched its first public presentation at the Tivoli last week—just two hours after Flight had gone to press with last week's issue! Not that this film was designed primarily to stimulate A.T.C. recruiting. Produced with the full co-operation of the R.A.F. and the Air Ministry, it is expressly stated that it has been presented to the A.T.C. by Mr. J. Arthur Rank, head of Gaumont-British, as a personal tribute to the good work of the Corps' officers, instructors and cadets. So possibly the suggestion ot a recruiting atmosphere must be credited very largely to the familiar news-reel voice of E. V. H. Emmett, whose commentary probably made many a greying head wish he were back in his teens It did me!—despite the optical distortion inflicted by a side seat. Possibly the best thing about "Sons of the Air" is that no attempt has been made to indulge in any of those profes sional tricks—clever camera angles, etc.—which are out of place in a documentary film ot this kind. It has been directed with a straightforward simplicity which gives it strength and dignity. Moreover, its characters are real people, doing what H T 473 "speed" or "r.p.m. control." The pilot, of course, does not control the airscrew blade pitch—he is uninterested in the pitch—all he is concerned with is controlling the engine speed, and it is felt that much less all-round confusion would be caused if the erroneous '' pitch control lever'' were dropped and with it the false impression the title conveys. Feathering So far, no mention has been made of the feathering side of airscrew operations. When an engine failure occurs, the reason for feathering the airscrew blades, i.e., turning them so that they are virtually '' edge-on '' to the line of flight, is that with the blades in such a position the very least possible air flow resistance is offered, and further more there is no tendency for the airscrew to " windmill," and thus possibly increase the damage to the engine. The range of engine speed governed by the c.s.u. is represented by the degree of travel of the pilot's speed con trol lever. This is fitted in a quadrant the rear of which has a gate through which the control lever may be passed by lifting a stop catch. When it is desired to feather, the catch must be lifted and the lever moved rearward through the gate. This final travel actuates the racked sleeve in the c.s.u. and moves the piston valve to the positive coarse pitch position. However, due to the fact that the c.s.u. is engine driven it would be useless to rely on the c.s.u. pump for delivery of feathering oil, and for this reason a separate electrically driven, high-output pump is provided for the purpose. This feathering pump is brought into action by the pilot depressing a special feathering switch in the cockpit, whereupon the pump immediately feeds oil to the c.s.u. whence it is directed to the coarse-pitch side of the piston in the pitch-changing mechanism of the airscrew, and so rapidly rotates the blade to the feathered position. The feathering operation takes approximately eight seconds. (To be continued.) the Air .C. : Impressive London Premiere they normally do, and very likely not one of them had ever found himself in front of a movie camera in his life before. The film takes one through the training of the A.T.C. cadel from the moment he joins uutil he is ready to pass out into the R.A.F. (and but for the present exigencies of the war, would normally do so), and if 1 have any criticism to offer it is that the sequences included one showing cadets receiving airscrew instruction in a "classroom" bomber which might be described as a cousin, slightly removed, to the Link. Now this is all very nice and interesting, but it is not part of the standard A.T?C. course. By no means every A.T.C. squadron is fortunate enough to possess such equipment, yet the way in which this scene was dovetailed in implied that it was ' all part of the A.T.C. service"—tu coin a phrase. 1 felt that it should have been made quite clear that this was the sort ol " extra" to the normal course of training that some of the more fortunately placed squadrons are able to offer their cadets. The film ends with a special parade on Wellington Barracks parade ground at which Air Marshal Sir Leslie Gossage, Direc tor-General and Chief Commandant of the A.T.C., reads the citation of the V.C posthumously awarded to Fit. Sgt. A. L. Aaron, the first ex-A.T.C. cadet to win it. The march past, at which Sir Leslie and the V.C.'s father take the salute, makes a moving and impressive finale. The occasion of the film's premiere was also impressive, from the seried ranks of gold-braided R.A.F. caps parked in the foyer, to the single rank of smart A.T.C. buglers whose clarion notes heralded the film from the decorated orchestra pit. Afterwards, Capt. H. H. Balfour, Under-Secretary for Air, paid a tribute to the A.T.C. and said that they looked forward to seeing the A.T.C. playing a vital role in peacetime in supply ing recruits of the finest quality for both military and civil aviation in this country. N. D. R.
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