X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Wed, 08 Jun 2011 08:25:10 -0400 Message-ID: X-Original-Return-Path: Received: from nm2.bullet.mail.ne1.yahoo.com ([98.138.90.65] verified) by logan.com (CommuniGate Pro SMTP 5.4.0) with SMTP id 5013251 for lml@lancaironline.net; Wed, 08 Jun 2011 06:38:56 -0400 Received-SPF: none receiver=logan.com; client-ip=98.138.90.65; envelope-from=casey.gary@yahoo.com Received: from [98.138.90.52] by nm2.bullet.mail.ne1.yahoo.com with NNFMP; 08 Jun 2011 10:38:20 -0000 Received: from [98.138.89.198] by tm5.bullet.mail.ne1.yahoo.com with NNFMP; 08 Jun 2011 10:38:20 -0000 Received: from [127.0.0.1] by omp1056.mail.ne1.yahoo.com with NNFMP; 08 Jun 2011 10:38:09 -0000 X-Yahoo-Newman-Property: ymail-3 X-Yahoo-Newman-Id: 204827.67295.bm@omp1056.mail.ne1.yahoo.com Received: (qmail 66933 invoked by uid 60001); 8 Jun 2011 10:38:09 -0000 DomainKey-Signature:a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com; h=Message-ID:X-YMail-OSG:Received:X-Mailer:References:Date:From:Subject:To:In-Reply-To:MIME-Version:Content-Type; b=uxJXYMMQJc3gqvm31rHExdMeJZ2+54y8EorEkTDJYp/f0yvr3JbyipF14iHuskJZoSaGAvj+Wuu51ccg9tgtJzpOnmamI52RRjv5oRRKhUeDSO3V1wEtBQzuTc/n0eJ0vsfu/mh/I4E3UkFkzb3crMyN6ssOT5lqM51sNTJhFKw=; X-Original-Message-ID: <994268.66156.qm@web125602.mail.ne1.yahoo.com> X-YMail-OSG: uuqtVvMVM1lsHI9cpLcN3z8KCRNdO.HggLyBE2kaKymRPbr hWX1u7LRsehtleYANggeuKb6DVBPRQwq9eZYfjPUBMpDgovNFT4XrcoWC4sK t5ui8OPBrlXfBQfnpqFZgxkhefh3NFZdPlh4mp_OQzId.IObshU55Z7Ktylz RMEqTt0ZuOB.jplCENi9JQ35_ctfPnVktxuvwl_9cmSJwAmLZcJMoU0mcqZn 2c24nL_Zi2NGwQ_hvVOnpRFRGV_N.27YGwGDILAkL4bW7rJvoJFp4eJE8mb. QO9S7gA37tGNbLUcNrJ0zKwynmdDnttsMYLyLB3hQKoPJgV4sk.TBsA0H6mG vN_7Y6EstY1cqrgTP8uJRM6qL52M- Received: from [97.122.154.57] by web125602.mail.ne1.yahoo.com via HTTP; Wed, 08 Jun 2011 03:38:08 PDT X-Mailer: YahooMailRC/570 YahooMailWebService/0.8.111.303096 References: X-Original-Date: Wed, 8 Jun 2011 03:38:08 -0700 (PDT) From: Gary Casey Subject: Re: L-IV Choice of Engine X-Original-To: Lancair Mailing List In-Reply-To: MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="0-706737465-1307529488=:66156" --0-706737465-1307529488=:66156 Content-Type: text/plain; charset=us-ascii Certainly there is some testing that goes into propeller selection, but I'm not sure I would categorize it as "a lot." That would imply that most combinations are bad, there is no science that allows a correct selection, and therefore it is just luck. Sure, there is testing that confirms performance optimization, but that's not what we are talking about here. If my memory serves correctly, to certify a propeller installation in a given airframe the FAA requires a torsional study be performed, which involves internal sensor be installed to measure the torsional vibration of the crankshaft. This costs money, so STC's for new propellers come slowly. Frankly, I don't understand at all the requirement for the prop/engine/airframe combination to be verified. The engine is stiffly connected to the prop (big bolts, metal/metal joints, etc) and softly connected to the airframe (rubber), so how could the torsional vibrations involve the airframe? In any event, I recall that the number of operational hours required is small, something like 50. And then to confuse and obscure the issue further, the only FAA requirement for experimental aircraft is that if the engine/prop combination (not airframe) has been certified the fly-off requires only 25 hours - otherwise 40. So they sort of admit that the airframe has nothing to do with it. Finally, I don't know of any prop failures related to the engine to which they were attached. So with great trepidation I might slightly disagree with Brent in that I doubt that attaching an otherwise-successful prop to a V8 engine will almost certainly result in a prop failure. In the end, we have to decide on the odds with which we are willing to play. Is being "pretty sure" something will work good enough? For some it seems so, but for others not. Gary Casey Ted, A lot of testing goes into propeller selection for engines. Jeff Edwards --0-706737465-1307529488=:66156 Content-Type: text/html; charset=us-ascii
Certainly there is some testing that goes into propeller selection, but I'm not sure I would categorize it as "a lot."  That would imply that most combinations are bad, there is no science that allows a correct selection, and therefore it is just luck.  Sure, there is testing that confirms performance optimization, but that's not what we are talking about here.  If my memory serves correctly, to certify a propeller installation in a given airframe the FAA requires a torsional study be performed, which involves internal sensor be installed to measure the torsional vibration of the crankshaft.  This costs money, so STC's for new propellers come slowly.  Frankly, I don't understand at all the requirement for the prop/engine/airframe combination to be verified.  The engine is stiffly connected to the prop (big bolts, metal/metal joints, etc) and softly connected to the airframe (rubber), so how could the torsional vibrations involve the airframe?  In any event, I recall that the number of operational hours required is small, something like 50.  And then to confuse and obscure the issue further, the only FAA requirement for experimental aircraft is that if the engine/prop combination (not airframe) has been certified the fly-off requires only 25 hours - otherwise 40.  So they sort of admit that the airframe has nothing to do with it.  Finally, I don't know of any prop failures related to the engine to which they were attached.  So with great trepidation I might slightly disagree with Brent in that I doubt that attaching an otherwise-successful prop to a V8 engine will almost certainly result in a prop failure.  In the end, we have to decide on the odds with which we are willing to play.  Is being "pretty sure" something will work good enough?  For some it seems so, but for others not.
Gary Casey

Ted,
 
A lot of testing goes into propeller selection for engines.
 
Jeff Edwards
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