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Date: Fri, 18 Dec 2009 10:18:44 -0500
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From: "Bill" <n5zq@verizon.net>
References: <list-4026454@logan.com>
Subject: Prop and Glide considerations
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Hiya Scott,

Good info on glide ratios. You advocate stopping the prop. In most =
cases, this would produce slightly less drag than a windmilling, but =
high angle (prop control pulled back) prop. Problem is, I don't think =
that it can be done in our planes. I know for sure that I can't do it in =
our 320...I've tried. With the engine shut down and prop back I've =
slowed to just above a stall and the prop just keeps going. I've got an =
MT prop which will go to a higher angle than most others, maybe this is =
why. Has anybody been able to stop a prop (assuming no engine damage and =
a non-feathering prop in any kind of Lancair?=20

My guess is that in an actual emergency, it would probably be best not =
to attempt it. Speaking for myself, I've got just so much concentration =
and the prop stopping maneuver would use up a bunch. When thinking about =
engine out procedures we always think about maximizing the glide. This =
is, of course, the proper thing to do to give you more time to think and =
plan. There are times, however when it is advantagious to MINIMIZE the =
glide ratio. Pushing in the still spinning prop will allow you to do =
this.=20

When I was an examiner I conducted hundreds of private and commercial =
flight tests always including a simulated forced landing.  Getting too =
high was just as common as a too low and the actual outcome would likely =
be worse. Having the ability to shove the prop forward gives you one =
more tool to modify your descent. That option is not available if the =
prop is stopped (the possible exception would be a feathering prop with =
an accumulator).

I agree with Bill Kennedy. Learn how YOUR airplane glides and practice =
simulated forced landings. In our 320 with the engine at idle and the =
prop full aft I get a descent rate down of 500 fpm at 110 kts. With the =
engine SHUT DOWN it's 900 fpm. My suggestion would be to learn what your =
airplane does with the engine actually shut down, obviously at high =
altitude, good weather, and over an airport with a long runway. Once you =
have that number, you can do your engine out practice with the engine at =
idle and the prop adjusted to the RPM that gives you the same rate of =
descent that you discovered in your shut down test. Your practice then =
should give you very realistic glide performance.=20

Bill Harrelson
N5ZQ 320 1,750 hrs
N6ZQ  IV under construction
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<DIV>Hiya Scott,</DIV>
<DIV>&nbsp;</DIV>
<DIV>Good info on glide ratios. You advocate stopping the prop. In most =
cases,=20
this would produce slightly less drag than a windmilling, but high angle =
(prop=20
control pulled back) prop. Problem is, I don't think that it can be done =
in our=20
planes. I know for sure that I can't do it in our 320...I've tried. With =
the=20
engine shut down and prop back I've slowed to just above a stall and the =
prop=20
just keeps going. I've got an MT prop which will go to a higher angle =
than most=20
others, maybe this is why. Has anybody been able to stop a prop =
(assuming no=20
engine damage&nbsp;and a non-feathering prop in any kind of Lancair? =
</DIV>
<DIV>&nbsp;</DIV>
<DIV>My guess is that in an actual emergency, it would probably be best =
not to=20
attempt it. Speaking for myself, I've got just so much concentration and =
the=20
prop stopping maneuver would use up a bunch. When thinking about engine =
out=20
procedures we always think about maximizing the glide. This is, of =
course, the=20
proper thing to do to give you more time to think and plan. There are =
times,=20
however when it is advantagious to MINIMIZE the glide ratio. Pushing in =
the=20
still spinning prop will allow you to do this. </DIV>
<DIV>&nbsp;</DIV>
<DIV>When I was an examiner I conducted hundreds of private and =
commercial=20
flight tests always including a simulated forced landing.&nbsp; =
Getting&nbsp;too=20
high&nbsp;was just as common as a too low&nbsp;and the =
actual&nbsp;outcome would=20
likely be worse. Having the ability to shove the prop forward gives you =
one=20
more&nbsp;tool to modify your descent. That option is not&nbsp;available =
if the=20
prop is&nbsp;stopped (the possible exception would be a feathering prop =
with an=20
accumulator).</DIV>
<DIV>&nbsp;</DIV>
<DIV>I&nbsp;agree with Bill Kennedy. Learn how YOUR airplane glides and =
practice=20
simulated forced landings. In our 320 with the engine at idle and the =
prop full=20
aft I&nbsp;get&nbsp;a descent rate down&nbsp;of 500 fpm at 110 kts. With =
the=20
engine SHUT DOWN&nbsp;it's&nbsp;900 fpm. My suggestion would be to learn =
what=20
your airplane does with the engine actually shut down, obviously at high =

altitude, good weather, and over an airport with a long runway. Once you =
have=20
that number, you can do your engine out practice with the engine at idle =
and the=20
prop adjusted to the RPM that gives you the same rate of descent that =
you=20
discovered in your shut down test. Your practice then should give you =
very=20
realistic glide performance. </DIV>
<DIV>&nbsp;</DIV>
<DIV>Bill Harrelson</DIV>
<DIV>N5ZQ 320 1,750 hrs</DIV>
<DIV>N6ZQ&nbsp; IV under construction</DIV></BODY></HTML>

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