Clearing the plugs on runup is common. But I don't see the point in landing to do a runup on the ground. Does that involve leaning or something?
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Crashes in the News - Thread
- Thread starter choppergirl
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On the topic of oil systems, are these oil actuated props? Is the pitch controlled by oil pressure?
Perhaps a malfunctioning prop was mistaken for wet mags.
It would probably feel similar, as the prop going too deep of a pitch would cause a sudden bogging of the motor.
Typically, oil actuated props feather when they experience oil loss, but if the output was clogged the pressure would skyrocket instead and push the prop to max instead of minimum.
At least one prop was feathered, but this doesn’t mean that was the correct engine, and it doesn’t rule out another engine being the issue. Pilots have sometimes performed emergency checklists on the wrong engines, which has actually caused crashes before in the past.
The aircraft should fly well on 3 engines. Being unable to hold altitude on 3 engines sounds like there was a second engine involved. And if that second engine was otherwise running well, the prop setting would be the most likely culprit for a loss of power.
Perhaps a malfunctioning prop was mistaken for wet mags.
It would probably feel similar, as the prop going too deep of a pitch would cause a sudden bogging of the motor.
Typically, oil actuated props feather when they experience oil loss, but if the output was clogged the pressure would skyrocket instead and push the prop to max instead of minimum.
At least one prop was feathered, but this doesn’t mean that was the correct engine, and it doesn’t rule out another engine being the issue. Pilots have sometimes performed emergency checklists on the wrong engines, which has actually caused crashes before in the past.
The aircraft should fly well on 3 engines. Being unable to hold altitude on 3 engines sounds like there was a second engine involved. And if that second engine was otherwise running well, the prop setting would be the most likely culprit for a loss of power.
If an engine was running rough and needed a "blow out" would it be shut down and feathered, or left running ?
Clearing plugs for DC-6
A malfunctioning prop would not trail smoke from number 4.
Number three shut down.
See https://www.homebuiltairplanes.com/forums/threads/crashes-in-the-news-thread.25303/page-141#post-495269
BJC
We did not shut down an engine if "it was needed".
So he probably meant "burn out procedure". Does that need to be done on the ground?
Looking at the B-17 manual (link in a previous post) the propellers were feathered with hydraulic oil not engine oil so had a separate oil supply for feathering system. The Caribou has hydraulic oil to feather the 2000's.
I am not sure what he meant. But I have never tried to clear an engine airborne. Bad plugs can be an indication of other problems, and why would you want another problem to manifest itself airborne? He could have meant something else entirely as well, especially if he "announced it", round motor crews are generally tight lipped on the radio, he may have been telling the ground crew to prepare for some procedure?
That depends. If it was blowing oil out the hub seals or a vent, it would get smoky very quickly as the oil hit the exhaust. Or if oil fed back up a breather into the intake system and it ingested oil.
Of course we won’t know until they open up that engine and do the tear down to see what happened.
The carbon patterns from blowing oil will be different than those from sitting in the flames on the ground.
Wanttaja
Well-Known Member
"Pushing the [feathering] switch stars an electric pump in the nacelle which supplies hydraulic power for the feathering operation." - Pilot's Manual
May use engine oil as a hydraulic fluid for this operation, but that's not the way I would read it.
Ron Wanttaja
RJW
Well-Known Member
Not sure but I think you might be confusing the Wright 1820 which is used on B17s and the 1830 which is a Pratt & Whitney motor.
Rob
I should have read how it was worded in the pilots manual instead of going off what I knew, sorry.
I just checked my maintenance manual and it is a little confusing if you don't know how feathering props work. Common sense says a system that is tested in flight and on the ground wouldn't pump hydraulic fluid into the engine.
Brandon
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I’m surprised the system doesn’t auto feather after loss of pressure.
What is the default position after oil loss?
What is the default position after oil loss?
Looking it over it is ambiguous, I know that sometimes hydraulic fluid is used to feather props instead of engine oil but the reference here isn't clear.
But only if the engine dies or is cut, correct?
I wonder what angle it goes to with the engine still operational but the hub is clogged or depressurized.
Engine oil is the "hydraulic" fluid used for feathering and unfeathering. As stated, pushing the feathering switch latches in the feathering pump and when blades reach feather stops pressure increases to the point of activating a pressure sensitive switch that turns off pump.
Unfeathering is more deliberate in that pilot has to push in and hold switch until prop comes out of feather.
Terry
Yeah, sorry, it is confusing. Having worked on the system its easy for me to forget how poorly they describe things in the manuals. You really don't fully understand until you've actually seen one work.
Brandon
