Return-Path: Sender: (Marvin Kaye) To: lml@lancaironline.net Date: Sat, 07 Aug 2004 00:32:38 -0400 Message-ID: X-Original-Return-Path: Received: from smtp106.mail.sc5.yahoo.com ([66.163.169.226] verified) by logan.com (CommuniGate Pro SMTP 4.2) with SMTP id 355603 for lml@lancaironline.net; Sat, 07 Aug 2004 00:09:31 -0400 Received-SPF: none receiver=logan.com; client-ip=66.163.169.226; envelope-from=djmolny@yahoo.com Received: from unknown (HELO ddzfqt21) (djmolny@24.9.182.247 with login) by smtp106.mail.sc5.yahoo.com with SMTP; 7 Aug 2004 04:09:00 -0000 From: "DJ Molny" X-Original-To: "'Lancair Mailing List'" Subject: RE: [LML] Prop pitch with engine failure X-Original-Date: Fri, 6 Aug 2004 22:08:59 -0600 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0045_01C47C01.F9F067B0" X-Mailer: Microsoft Office Outlook, Build 11.0.6353 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1441 thread-index: AcR8HJ5NM+q6K2yTQQO2xlTqmqWPtwAF0UtA In-Reply-To: X-Original-Message-ID: This is a multi-part message in MIME format. ------=_NextPart_000_0045_01C47C01.F9F067B0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit There are at least other ways to force the prop to coarse pitch in the event of oil pressure loss: counterweights and a pressure accumulator. And the accumulator is obviously time-limited; once the pressure is used up the prop would return to fine pitch. Hartzell used an accumulator with their early 'Claw' model props, but changed to counterweights after some overspeed incidents. That said, your basic point is correct: any additional mechanism to put the blades into coarse pitch results in extra weight. -- DJ _____ From: Lancair Mailing List [mailto:lml@lancaironline.net] On Behalf Of Ted Noel Sent: Friday, August 06, 2004 19:15 To: Lancair Mailing List Subject: [LML] Prop pitch with engine failure I spent some time with Harry Griswold of AeroComposites at Lakeland this year discussing prop pitch with engine failure. It turns out that the answer may not have to do with philosophy of handling emergencies but with mechanical complexity (cost) and weight. If you spin a prop without a governor, the mechanical forces will drive it to flat pitch. That means that there must be a force applied to drive the prop back to coarse pitch. This is typically done by using oil pressure to drive pistons that move the prop. Of course, when the engine stops, the oil pressure goes away, and the prop spins to flat pitch if it is windmilling. The only way to reverse this behavior is to have a massive spring in the hub to force the prop to coarse pitch at engine out. Then the pistons use engine oil to drive the prop to fine pitch. This spring increases complexity (cost) and weight. Ted Noel L-IV-P Eagle at airport, starting ground checks N540TF ------=_NextPart_000_0045_01C47C01.F9F067B0 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

There are at least other ways to force the = prop to=20 coarse pitch in the event of oil pressure loss: counterweights and a = pressure=20 accumulator. And the accumulator is obviously time-limited; once = the=20 pressure is used up the prop would return to fine pitch. Hartzell = used an=20 accumulator with their early 'Claw' model props, but changed to = counterweights=20 after some overspeed incidents.

That said, your basic point is correct: any = additional=20 mechanism to put the blades into coarse pitch results in extra=20 weight.

-- DJ

From: Lancair Mailing List=20 [mailto:lml@lancaironline.net] On Behalf Of Ted = Noel
Sent:=20 Friday, August 06, 2004 19:15
To: Lancair Mailing=20 List
Subject: [LML] Prop pitch with engine=20 failure

I spent some time with Harry Griswold = of=20 AeroComposites at Lakeland this year discussing prop pitch with engine = failure.=20 It turns out that the answer may not have to do with philosophy of = handling=20 emergencies but with mechanical complexity (cost) and = weight.

If you spin a prop without a governor, = the=20 mechanical forces will drive it to flat pitch. That means that there = must be a=20 force applied to drive the prop back to coarse pitch. This is typically = done by=20 using oil pressure to drive pistons that move the prop. Of course, when = the=20 engine stops, the oil pressure goes away, and the prop spins to flat = pitch if it=20 is windmilling.

The only way to reverse this behavior = is to have a=20 massive spring in the hub to force the prop to coarse pitch at engine = out. Then=20 the pistons use engine oil to drive the prop to fine pitch. This spring=20 increases complexity (cost) and weight.

Ted Noel

L-IV-P Eagle

at airport, starting ground = checks

N540TF

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