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Keven, and Kevin,
The manual says it. However, my flight instructor (who is also an A&P) taught me that it is not necessary to exercise the prop to extent implied in the POH during runup, that in fact it is harmful. So, what I mean by 300 - 400 RPM drop is I only move the lever enough to verify the governor on each engine is working, and that there is warm oil in it. Basically, I move it enough to hear the prop sound change, then move it back. On the first flight of the day I do this three times (I picked that up from the O-2 flight manual), and the rest of the day I do it once.
My instructor told me that if the governor moves that much, it is almost assuredly going to move all the way to the feather position, and that moving it all the way there stresses the engine excessively, and does not test the feather locks anyway, so you are still not sure if it will stay feathered in a real emergency.
When Jim questioned this practice, I checked with three additional AI's in two shops (I only intended two, but a second happened to be visiting a shop that I went to locally). All three listed a litany of problems with running the engine at low RPM and moderate throttle. As best I can remember, they were:
- problems with counterweights
- excessive crankcase pressure
- excessive vibration the engine was not designed for
- more wear and tear on the engine because of all of the above
There was probably more, but I was not taking notes.
As I said in previous message, the book specifies Jim's procedure, so there should be nothing wrong with doing it, in should be something *right* in doing it.
What convinced me originally was my flight instuctor's comment that moving the prop control all the way does not really guarantee the prop will stay feathered, and does not test much more than moving it part way does.
Jim is convinced that testing all the way into feather tests "the feathering mechanism". Maybe he can elaborate more on what that is. I am not a mechanic, and I may misunderstand how feathering works. I thought that when you feathered a prop, the governor was doing nothing more than moving the prop to "feathered" pitch (by removing all oil pressure to the prop) and that there is a locking mechanism that holds the blades feathered on shutdown rather then letting them return to fine pitch as they normally do. But according to the guys I am talking to, you can't really test the locking mechanism unless you shut the engine down completely.
Kevin (everybody on this website seems to be named Kevin)
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