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Aviation History
1944
1944 - 2384.PDF
536 FLIGHT NOVEMBER I6TH, 1944 MODERN AIRSCREWS — ! PILOTS SPEED CONTROL / TO DECREASE RPM AT WHICH GOVERNING TAKES PLACE i>. TO INCREASE S.R M 'AT WHICH GOVERNING TAKES PLACE ly/Yv'ssS FEATHERING VALVE (CLOSEDJ of the slot length, the "remaining amount of slot being turned at an angle to the normal helical path. The result of this is that the inner cam only rotates so far under the influence of piston movement at normal pres sures, and when the rollers come up against the angle in the slot they will normally go no farther; thus a coarse pitch limit is "built in*' the cams. However, when the piston is subjected to the high-pressure delivery of the leathering pump, suffi cient power is applied to cause the rollers to make the abrupt turn in the cam slots, and this latter slot path being of much less "lead " than the normal, feathering rotation of the inner cam is quicker, and with it, rotation of the blades to the feathered position. The feathering pump is automatically cut out when the blades are feathered and pressure builds up to a value sufficient to operate a pressure cut-out switch in the pump circuit. Unfeathering When the pilot wishes to feather the airscrew he first presses a push-button to bring into action the feathering pump, then closes the throttle and finally switches off the engine. The operation of the mechanism is then as described. To unfeather the blades is rather a different story as it in volves the distributor valve assembly referred to earlier. The sequence is that the pilot makes sure his speed- control lever is in the "constant-speed" position then again presses the button, bringing into action the feather ing pump. When the blades are in the feathered position the oil pressure on both sides of the piston sinks to zero— the feathering non-return valve in the c.s.u. closed when the feathering pump delivery was cut-off and the oil pas sage was thus opened to drain, likewise as the engine stopped the oil system pressure fell to zero. Consequently, when the feathering pump is again en gaged to unfeather the blades, the pressure is built up behind the piston which is at its forward limit of travel, but the pilot must continue to hold down the feathering switch to prevent the pressure cut-out operating. The high pressure generated then acts over the area of lands SPEED CONTROL RACK FROM ENGINE OIL EXPELLEDEZTi^J FROM AIRSCREW: FROM ENGtNE TO ENGINE CPANKCASE AND SUMP FROM- FEATHERING! PUMP i AIRSCREW OIL FROM ENGINE OVERSPEED TOEZZSZSZ AIRSCREW FEATHERING AND UNFEATHERING These diagrams show the c.s.u. operative conditions and schematic oil flow through the unit for various stages of operation. The c.s.u. gear pump increases the pressure of oil fed from the engine lubrication system, and when no feed from the pump is being used the relief valve opens and vents the oil back to the suction side. on the distributor valve, moving the valve against a spring so that ports are uncovered which allow the feathering pump oil delivery to be transferred to the front of the piston and open the rear side of the piston to engine drain. Thus the oil flow is reversed. This forces the piston back so unfeathering the blades which, as they start to " wind mill," assist the action by their centrifugal moment. When the engine is turning over at reasonable r.p.m. the pilot releases the feathering pump switch so that delivery is cut off, and the distributor valve at once snaps back to its normal position. With the stoppage of the feathering pump and the increase of engine oil pressure, return to the constant-speeding pitch setting of the blades is rapid. (To be continued.) London-Liverpool Air Service MONDAY last saw the reinstatement ol the passenger air service between London and Liverpool—the first internal civil air service to be resumed since war began and a pleasant indication of " things to come." Operated by Railway Air Services, the resumed service links up with the Liverpool-Belfast and Liverpool-Isle of Man services, both of which have been maintained on a wartime basis. Ten-seater de Havilland D.H.86 four-engined airliners are being used for the present between London and Belfast, E issengers changing aircraft at Liverpool. The service from iverpool to the Isle of Man, however, is operated by the smaller two-engined D.H. Rapide aircraft, which is more suit able for flying in and out of the small Manx airport. Aircraft leave Croydon at 9 a.m. every weekday and are due at Speke (Liverpool) at 10.45 a.m. Here passengers for Belfast must pass through certain security formalities before emplaning at n a.m. for the 1$ hr. sea crossing to Northern Ireland Passengers to*- the Isle of Man. however, can transfer immediately to the Manx aircraft, which is scheduled to reach *~ Ronaldsway at 11.45 a.m. Road transport is provided between the West End and Croydon, and between Liverpool, Belfast and Douglas and their respective airports, and is included in the following fares: London-Belfast, £8 single, £13 return; LonJon-Isle of Man, £6 7s. 6d. single, ^ro 5s. return; London-Liverpool, £4 10s. single, £7 return. For the return journey, a new service leaves Belfast at 1 p.m. which is due at Speke at 2.30 p.m., and connects there with the London service, arriving at.Croydon at 4.30 p.m. Passenger::' taking return tickets who desire to make the return journey by steamer and rail can exchange their tickets and" obtain a refund of the difference due to them, or, alternatively, passengers in possession of the return halves of rail and steamer tickets between the points the air services operate can return by air—subject to accommodation being available—on payment of a supplement. This feature ol the Railway Associated Air Services is extremely popular. Tickets can be obtained at Olley Air Services, Ltd., 7b, Lower Belgrave St., and the Main London railway stations, 24, Donegall Place, Belfast, and Lime Street, Liverpool.
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