Lo-n-Slo

Not quite that simple - some makes of prop go full fine when the oil pressure is lost, some go full coarse - depends on the governor mechanics. I was going from failing and possibly faulty memory saying the Hamilton Standards on a P-51 goes full coarse . The statement was based on my (admittedly limited) knowledge of the governor mechanism and having watched a number of deadsticks landings over the years at Reno. Will inquire to get a definitive answer from the warbird mechanics who will know for sure. I do know that the Rotol contra rotating props on the Griffon engined Red Baron went full flat when it lost all oil pressure, which slowed the aircraft enough that Steve Hinton was unable to make the runway, resulting in a crash that only by a major miracle he lived through. Pretty sure the P51 HS works the opposite, going full course, so the pilot with a dead engine has a reasonable chance of gliding back to a decent approach. Also, I believe for props that could be fully feathered (e.g. most WWII era multi-engine aircraft), if the main oil supply was lost there needed to be some form of auxiliary oil pressure source to drive the blades to the full feather position. cheers Lo

Hamiton Standard props (as on the P51-D) go feathered or full coarse pitch when they lose pressure. You DO NOT want a full fine or flat pitch prop acting as a BIG airbrake when you lose a motor:( The prop governor does use engine oil as its supply, but has its own internal pressure pump that produces the regulated high pressure oil that controls the pitch of the blades. As long as the engine system is supplying oil at any pressure above zero, the governor will function. Run the engine at zero oil pressure plus any flight sustaining power setting for more than a few seconds and there will be much bigger problems to deal with than a prop at full coarse :music_whistling::smilewink:. cheers Lo

Yes, its kind of a picky distinction, but technically the P lever sets Propeller RPM rather than engine rpm. The technical distinction is important because the speed control is achieved by the prop governor that varies the pitch of the blades rather than by adjusting any engine operating parameters (such as fuel, throttle or ignition settings). As there is a direct geared connection between the prop and the crankshaft, engine RPM is directly related to prop RPM (by the ratio of the gears in the nose case), so by controlling one you effectively control the other. cheers Lo

Prop governor is much smaller than the spinner; the governor itself is quite small and sits on the side of the engine nose case and is protected by a fairly large percentage of the prop disc (the cuffed Hamilton Standard prop blades filled most of the disc area at the prop root) and spinner; the relatively fragile valves and oil galleries are located right in the center of the prop hub. The rest of what is in the spinner cavity if fairly robust - you'd be more likely to lose a prop blade than to lose governor oil pressure when these bits are hit and it would take something in the order of a 20mm HE cannon round to do that much damage. The illustration below shows most of the pieces without the spinner, which would be about the diameter of the nose case and come out past the hub dome: cheers Lo