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dongirod(at)bellsouth.net
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 Posted: Tue May 23, 2006 6:41 pm Post subject: Advice from Gear-Heads... |
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Tylor;
I am not an expert by any means, but logic tells me that probably the most
'positive prop pressure' you could inflict on a gear box is going to the
feather position, that is ALL engine running prop.
Don
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STOLHorse(at)aol.com
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| Posted: Tue May 23, 2006 7:57 pm Post subject: Advice from Gear-Heads... |
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I check the feathering on the 685 at about 1200 - 1300 rpm. It's very
gentle and you can practically hear the blades change pitch before you see any rpm
drop.
You can pull the prop lever back to the detent just before feather and all
will stay the same because at that rpm the governor is still so far below its
minimum governing speed the prop stays at low pitch. When you pull back
below the detent, the governor dumps the oil pressure and the propeller will
gently start to feather. You can hear it plain as day and then bring it back out
of feather before the rpm decays too much. This proves that the feathering
function of the governor is working and that the rigging is correct on that
end. (I suppose there could be a mechanical defect in the propeller that
would stop the blades from moving before they hit the feathering stop but I'm
thinking that kind of problem would show itself in flight as poor constant speed
governing or inability to maintain low rpm at high air speeds.)
Anyway, I don't do this at every runup - only when the rigging needs to be
checked or after replacement of some component. And, if you want to actually
see it feather, you're practically at idle so you can just pull the prop
lever into feather and then mixture to cutoff (I like to open the throttle too
after the fuel is cutoff). The engine dies before the blades go all the way
and you can just watch the nitrogen and spring do the rest. I let it feather
on shut down for the oil changes, too.
To unfeather it, you need to bleed all the nitrogen out and get a guy on
each blade and turn them back towards low pitch until you hear the pitch stops
click into place.
Incidentally, the 685 the Commander maintenance manual is incorrect on
nitrogen pressure. The book says something like 80psi but that is for a prop
without the feathering spring. The props on the 685 DO have springs so the
correct pressure for these props is right around 40 psi depending on temperature.
The Hartzell book lists the pressure ranges.
Anyway, try it at low rpm in your 421 tylor and see if you like it. In my
opinion it is far less stressful on the engine than the average hot start!
Aaargh.
Best regards,
David Maytag
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rsrandazzo(at)precisionma
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| Posted: Tue May 23, 2006 8:45 pm Post subject: Advice from Gear-Heads... |
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David-
Interesting info- wasn't my question but the detail is appreciated.
Robert Randazzo
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WINGFLYER1(at)aol.com
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| Posted: Wed May 24, 2006 6:42 am Post subject: Advice from Gear-Heads... |
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+Hello Guys, I am a new 680 owner and very interested in prop and engine
management. When I taxi at 12 to 15 and the props forward I hear the gears
clanging on the left engine but not on the right side, I would appreciate any
advise and have already learned a lot from your comments . Thanks Gil Walker
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BillLeff1(at)aol.com
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| Posted: Wed May 24, 2006 8:24 am Post subject: Advice from Gear-Heads... |
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How true!
However ,be careful what kind of fuel the line boys put in it!!! Some are
not smart enough to tell the difference!!
Bill
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BillLeff1(at)aol.com
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| Posted: Wed May 24, 2006 8:25 am Post subject: Advice from Gear-Heads... |
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I am sur you baby will appreciate the TLC it is now getting! Keep up the
good work.
Bill Leff
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BillLeff1(at)aol.com
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| Posted: Wed May 24, 2006 8:36 am Post subject: Advice from Gear-Heads... |
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Cycling the props to feather in the GTSIO-520 in the 421 and the 685 does
not hurt the gear boxes. However, I recommend doing it at 1500 engine RPM to
reduce the load on the gears. It accomplishes what is necessary. That is: will
the prop feather. It is not necessary to have the prop go completely to
feather. That unnecessarily loads up the gear train but should not hurt it.
Once it starts to drop, return the prop control to full RPM.
Bill Leff
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