X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Wed, 17 Oct 2007 21:22:08 -0400 Message-ID: X-Original-Return-Path: Received: from elasmtp-kukur.atl.sa.earthlink.net ([209.86.89.65] verified) by logan.com (CommuniGate Pro SMTP 5.1.12) with ESMTP id 2390860 for lml@lancaironline.net; Tue, 16 Oct 2007 22:35:14 -0400 Received-SPF: none receiver=logan.com; client-ip=209.86.89.65; envelope-from=colyncase@earthlink.net DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=dk20050327; d=earthlink.net; b=NqwON012b/EBu4yytGrF/bbrB0BUIOCt/rnr23Vm8AEnVdexsEuLFm4Bvev5MBMf; h=Received:Message-ID:From:To:References:Subject:Date:MIME-Version:Content-Type:X-Priority:X-MSMail-Priority:X-Mailer:X-MimeOLE:X-ELNK-Trace:X-Originating-IP; Received: from [216.57.118.66] (helo=ccaselt2) by elasmtp-kukur.atl.sa.earthlink.net with asmtp (Exim 4.34) id 1Ihyk3-0000aH-1n for lml@lancaironline.net; Tue, 16 Oct 2007 22:34:39 -0400 X-Original-Message-ID: <031d01c81066$44ffe9f0$0302a8c0@nvidia.com> From: "Colyn Case on earthlink" X-Original-To: "Lancair Mailing List" References: Subject: Re: [LML] Re: prop drag X-Original-Date: Tue, 16 Oct 2007 22:34:40 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_031A_01C81044.BD82DDF0" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.3138 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.3138 X-ELNK-Trace: 63d5d3452847f8b1d6dd28457998182d7e972de0d01da940a7f3ee54e4b4da9a9ef10b483261e990350badd9bab72f9c350badd9bab72f9c350badd9bab72f9c X-Originating-IP: 216.57.118.66 This is a multi-part message in MIME format. ------=_NextPart_000_031A_01C81044.BD82DDF0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Bill, corrections/additions to this post: - the best info I can find is at http://218.6.160.140/jwb/techdoc/om.pdf - 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 -----=20 From: Colyn Case on earthlink=20 To: lml@lancaironline.net=20 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=20 > at startup and low RPM's- is there a control detent to prevent the = prop=20 > 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.=20 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. ------=_NextPart_000_031A_01C81044.BD82DDF0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Bill,
corrections/additions to this = post:
 
- the best info I can find is at http://218.6.160.140/jwb= /techdoc/om.pdf
- the prop locks engage below = 800=20 rpm
- (-2) props can be installed with an = unfeathering=20 accumulator.  I like that idea.  It would be nice if you could = just=20 program yourself to feather immediately whenever in doubt and then be = able to=20 undoit.
- there is supposedly a detent in the=20 control.  However, I haven't noticed it when operating my=20 prop.
- Alan said these don't really = feather.  I=20 wasn't able to find blade angles but I can say that when I feathered = mine and=20 shut it down it looked parallel to the airflow to me.   There = is a=20 counterweighted but not feathering version.  Maybe that is what = Alan was=20 talking about.
 
there was a debate earlier about the = tradeoffs of=20 having a feathered prop vs. just having one you can set to high = pitch.  One=20 member was able to complete a normal pattern after he lost oil = pressure but=20 still had power on climbout.   With a full-feathering prop, he = would=20 have had no power.
 
I decided to go feathering = because:
a) losing an engine in inhospitable = terrain seems=20 like a pretty big issue in a high speed single.
b) exposure time to problem (a) is = greater than=20 exposure time to=20 oil-pressure-failure-on-takeoff-but-the-engine-is-still-running.
c) I considered more forward cg a good=20 thing.
 
I do wish for a composite prop these = days,=20 though.
 
Colyn
----- Original Message -----
From:=20 Colyn=20 Case on earthlink
Sent: Tuesday, October 16, 2007 = 6:52=20 PM
Subject: [LML] Re: prop = drag

> I'm considering a = feathering prop but=20 I've never used one. What happens
> at startup and low RPM's- = is there=20 a control detent to prevent the prop
> from going = feathered? =20 -Bill Wade
 
Bill,  there's no detent in the=20 control.   I am not an expert so I'm posting this = so some=20 prop expert can correct me....
 
once you set the rpm below some = threshold, I've=20 been told it's going to keep going toward full feathered.   = I've=20 been told this happens about 1900 rpm.
 
There is, however, a detent in the=20 mechanism.  If the govenor setting is above some threshold, the = prop is=20 locked in a fine position as the rpm falls through about 1200 = rpm.  =20 Therefore you have to be above that rpm when you command full feather = or it=20 won't.
 
The Hartzell I have, will not = unfeather without=20 power.    With a strong battery you can crank it for a = long=20 time ( > 20 seconds)  to get enough oil pressure to change the = pitch=20 back to fine.   This was empiracally tested on one plane I = know=20 of.
 
So as I see it, the situation = relative to full=20 feathering props is:
pro: automatically goes to feather on = engine=20 out
pro: (or con depending) hub is = heavier than stock=20 so it moves your cg forward
pro: excellent gliding range from = high=20 altitude
con: goes to feather on low oil = pressure, even if=20 the engine is still making power
con: harder to restart in the air if = it feathered=20 because of lo oil passure
con: the hartzell version I have is = metal so that=20 is a rougher ride.
 
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