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Bill,
corrections/additions to this post:
- the prop locks engage below 800
rpm
- (-2) props can be installed with an unfeathering
accumulator. I like that idea. It would be nice if you could just
program yourself to feather immediately whenever in doubt and then be able to
undoit.
- there is supposedly a detent in the
control. However, I haven't noticed it when operating my
prop.
- Alan said these don't really feather. I
wasn't able to find blade angles but I can say that when I feathered mine and
shut it down it looked parallel to the airflow to me. There is a
counterweighted but not feathering version. Maybe that is what Alan was
talking about.
there was a debate earlier about the tradeoffs of
having a feathered prop vs. just having one you can set to high pitch. One
member was able to complete a normal pattern after he lost oil pressure but
still had power on climbout. With a full-feathering prop, he would
have had no power.
I decided to go feathering because:
a) losing an engine in inhospitable terrain seems
like a pretty big issue in a high speed single.
b) exposure time to problem (a) is greater than
exposure time to
oil-pressure-failure-on-takeoff-but-the-engine-is-still-running.
c) I considered more forward cg a good
thing.
I do wish for a composite prop these days,
though.
Colyn
----- Original Message -----
Sent: Tuesday, October 16, 2007 6:52
PM
Subject: [LML] Re: prop drag
> I'm considering a feathering prop but
I've never used one. What happens
> at startup and low RPM's- is there
a control detent to prevent the prop
> from going feathered?
-Bill Wade
Bill, there's no detent in the
control. I am not an expert so I'm posting this so some
prop expert can correct me....
once you set the rpm below some threshold, I've
been told it's going to keep going toward full feathered. I've
been told this happens about 1900 rpm.
There is, however, a detent in the
mechanism. If the govenor setting is above some threshold, the prop is
locked in a fine position as the rpm falls through about 1200 rpm.
Therefore you have to be above that rpm when you command full feather or it
won't.
The Hartzell I have, will not unfeather without
power. With a strong battery you can crank it for a long
time ( > 20 seconds) to get enough oil pressure to change the pitch
back to fine. This was empiracally tested on one plane I know
of.
So as I see it, the situation relative to full
feathering props is:
pro: automatically goes to feather on engine
out
pro: (or con depending) hub is heavier than stock
so it moves your cg forward
pro: excellent gliding range from high
altitude
con: goes to feather on low oil pressure, even if
the engine is still making power
con: harder to restart in the air if it feathered
because of lo oil passure
con: the hartzell version I have is metal so that
is a rougher ride.
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