| 摘要 |
<p>Turboprop and propfan engines generally incorporate blades which have variable pitch to improve operational efficiency. Variable pitch is achieved through a pitch control mechanism (40) at the root of the blade but such mechanisms may fail resulting in the blades turning to define a flat configuration with low drag and therefore the potential for engine damage through over-speeding. Traditional pitch lock and counter weight control mechanisms have disadvantages. By providing a helical bearing in which the mass and radial movement due to centrifugal radial force are utilised it is possible to generate a counter moment to the normal centrifugal turning moment (CTM) to ensure the blade (31; 51) remains in a configuration with at least some drag to limit engine rotational speed. The continuous helical bearing allows for a range of pitch angular positions to be used around a full 360° turn by providing a feathering counter moment from any of those angular positions.
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