Loss of oil pressure to the hub, coarse or fine pitch, that is the question?
This is for all the engineering guru's out there, we have had a lengthy discussion with our chief engineer this morning. For all the pilots that have been told that we know nothing of engines, props and a/c systems, let us unite and prove these engineers wrong. Below is an extract from the AFM on the Cessna 402B
Extract: Oil pressure from the propeller governor drives the blades towards the low pitch/fine (increasing RPM) while the springs and counterweights drive the blades towards high pitch/coarse (decreasing RPM)
So.... in the event of a loss of oil pressure centrifugal force assisted by counterweights and springs drive the propeller into high pitch/coarse (decreasing RPM) position. This also will stop the engine from exploding due to excessive overspeed of the propeller.
However we have been told by our engineers that all of the above is incorrect and that the good people at Cessna are also incorrect of their understanding of this rather important subject. The engineers believe that in the event of loss of oil pressure to the hub, the propeller counterweights and springs will drive the prop to a low pitch/fine (increasing RPM) i.e. upon shutting the engine down there is a subsequent loss of oil pressure and the propeller will remain in the low pitch/fine position.
Help us PPrune your our only hope....