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Aviation History
1948
1948 - 1870.PDF
; NOVEMBER 4TH, 1948 KEEP YOU TECHNICALLY INFORMED No. 10 a monthly digest of news from, the ZfjUAtoL? aero-engine division M? ••••••• ') T REVERSING PROPELLERS FOR "BRISTOL" SLEEVE VALVE ENGINES The recent development of reversing propellers promises many advantages in reducing landing runs and easing the difficulties of manoeuvring large aircraft on the ground or in the water. Such propellers are actuated by a special engine driven oil pump giving a high-pressure delivery when required, which overrides the fine pitch stop in the propeller, and holds the blades at a fixed negative pitch as long as the pump is in circuit. A very high rate of pitch change is provided to give the full benefit of reversing in the minimum time, and to prevent momentary overspeeding of the engine whilst the propeller is passing through zero pitch. The illustration shows a civil Centaurus engine of the 600 series, which embodies the necessary 25 H.P. drive and flange for the reversing pump on the engine front cover adjacent to the constant speed unit. The two flanges are interconnected by internal drillings, but those passages from the reversing UN-BRAKE VALVE & SOLENOID PROPELLER OPERATING CYLINDER 1 BRAKE VALVE & SOLENOID PROPELLER GOVERNOR UNIT DIAGRAM OF PROPELLER OIL SYSTEM pump, conveying oil to the transfer system at the iront ot the reduction gear, are of increased size (§" diameter Hercules, $" diameter Centaurus) to cope with the high rates of flow. Under normal constant speeding conditions, oil is conveyed from the constant speed unit through these internal drillings in the engine front cover to the reversing pump flange. The oil passes straight across the control valve of the reversing pump, as ' I 1 .\W\G PUMP ASD COXSTAXr Sl'thD USIT FLANGES shown in the diagram, and is con- veyed back again to the reversing pump flange, and then proceeds via the large diameter internal drillings in the engine reduction gear to the propeller. Further, under the normal constant - speeding con- dition, the reversing pump is working at no pressure and its power absorption is negligible. When it is desired to reverse or un-reverse the propeller, the con- trol valve in the reversing pump is moved in the appropriate direction, and the effect in either case is to isolate the constant speed unit and to bring into circuit the reversing pump, causing the propeller to change pitch rapidly by pumping oil at a high rate from one end of the propeller operating cylinder to the other. The necessary flange, drive and drillings have been incor- porated as standard on all Centaurus engines from type 600 onwards, and all Hercules from type 750. THE BRISTOL AEROPLANE COMPANY LIMITEDBRISTOL - - ENGLAND Vfc
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