X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from [24.51.79.189] (account marv@lancaironline.net) by logan.com (CommuniGate Pro WEBUSER 5.1.1) with HTTP id 1509765 for lml@lancaironline.net; Fri, 27 Oct 2006 23:32:17 -0400 From: "Marvin Kaye" Subject: Re: Prop Feathering To: lml X-Mailer: CommuniGate Pro WebUser v5.1.1 Date: Fri, 27 Oct 2006 23:32:17 -0400 Message-ID: In-Reply-To: References: MIME-Version: 1.0 Content-Type: text/plain;charset="iso-8859-1";format="flowed" Content-Transfer-Encoding: 8bit Posted for Gary Casey : Rick gave a most excellent description of prop controls that answered some of the questions I have had forever (why is that twin sitting there without the props feathered?). But your question was about adding an accumulator to hold a conventional non-feathering prop in the high pitch position after an engine failure. As was said there are always tradeoffs. First, the oil is fed to the prop through the front main bearing, using the bearing itself as a (leaky) seal. the accumulator would have to be very large, I would think, to be able to hold oil pressure on the prop for any length of time and you need it to work for maybe 15 minutes. How do the accumulators on a feathering prop work then? They are only there to unfeather the prop and to do that only have to supply a single dollup of oil, after which the pins in the prop stop it from going back to the feathered position. I guess the lesson for twin drivers is that you only get one chance to unfeather the prop - after you do that and can't get the engine to restart you can't change your mind and feather it again. When would you want to go to high pitch when there is no engine oil pressure? I think rarely, as most engine failures result in an engine that still spins and maintains oil pressure. The engine would have to stop turning, but then I'm not sure there is a big drag difference between high and low pitch positions - both are stalled and represent flat plate drag. If the engine loses oil pressure, but keeps on turning it won't be doing that for very long. I thought about all the tradeoffs and elected to keep it simple. Stayed with a conventional prop. Gary Casey On Oct 27, 2006, at 3:01 AM, Lancair Mailing List wrote: