X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Tue, 17 May 2005 14:36:56 -0400 Message-ID: X-Original-Return-Path: Received: from smtp105.mail.sc5.yahoo.com ([66.163.169.225] verified) by logan.com (CommuniGate Pro SMTP 4.3c5) with SMTP id 947514 for lml@lancaironline.net; Tue, 17 May 2005 14:26:51 -0400 Received-SPF: none receiver=logan.com; client-ip=66.163.169.225; envelope-from=sseffern@yahoo.com Received: from unknown (HELO StusComputer) (sseffern@66.188.114.248 with login) by smtp105.mail.sc5.yahoo.com with SMTP; 17 May 2005 18:26:04 -0000 X-Original-Message-ID: <073501c55b0e$28a3cb60$6601a8c0@StusComputer> From: "Stuart Seffern" X-Original-To: "Lancair Mailing List" References: Subject: [LML] Airplane Construction Philosophy X-Original-Date: Tue, 17 May 2005 13:28:00 -0500 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0732_01C55AE4.3F2B8FF0" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.2527 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2527 This is a multi-part message in MIME format. ------=_NextPart_000_0732_01C55AE4.3F2B8FF0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Tim, Just one problem with your theory of duplicative redundancy in = airplanes, engines. The common placement of engines is on the wings and = in this configuration you are 4 times more likely to die in a single = engine out in a twin engine airplane than the only engine out in a = single engine airplane. With two engines the extra weight is very = important, which translates into extra fuel usage (also weight) as well = as asymmetrical thrust and human reaction issues on failure. Instead of = extra reliability you actually INCREASE the odds of dying in a fatal = crash by adding redundancy. In electrical systems, redundancy does make great sense and is becoming = the long overdue norm in certified airplanes, Diamond, Lancair, Cirrus, = etc... Two plugs, two mags, and electrical/vac redundancy has worked = well in the past. I just spent 4 hours behind the Garmin G1000 = yesterday shooting 12 approaches and I will tell you that the = Chelton/Garmin/Avidyne systems are amazingly less complex than the wavy = steam gage needles, once you learn how to use them. Having a reliable = approach coupled to a good autopilot with great situational awareness at = all times is a great example of the benefits of the advances made = possible by reliable electrical system redundancy. Stuart Seffern Madison, WI www.LantzairFlyers.com =20 ----- Original Message -----=20 From: Timothy Spear=20 To: Lancair Mailing List=20 Sent: Monday, May 16, 2005 9:32 PM Subject: [LML] Airplane Construction Philosophy Hello all, Working in the computer field I was wondering why so much = time in the aircraft industry is concerned with minimizing the mean time = between failure (MTBF) on a single component. For example in the = computer field we have moved extensively to a concept called RAID = (Redundant Array of Inexpensive Disks), in the "old" days a mainframe = disk drive with an average of a one MTBF every million hours cost tens = of thousands, versus a PC drive had an MTBF of a thousand hours and sold = for a few hundred. With RAID you would mirror the data between two PC = drives, and the chance then of a both failing at the same time was back = up to a million hours. Two PC drives would cost significantly less than = the equivalent mainframe, the result is that the cost of disk drives for = servers has gone down significantly. In addition, computer staff has = become used to a failure mode for disk drives resulting in reduced data = loss and better recovery procedures. In the aircraft industry we have = continued to engineer for the MTBF of a million hours, with two = consequences. One, everything is very expensive, two pilots are not used = to any failures; so when a failure occurs the pilot does not know how to = effectively deal with it. Therefore, why do we not accept a lower MTBF = and have two complete avionics systems, fly by wire controls, engines.. = The point could continue to everything except core structural elements. =20 =20 Tim ------=_NextPart_000_0732_01C55AE4.3F2B8FF0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Tim,
 
Just one problem with your theory of = duplicative=20 redundancy in airplanes, engines. The common placement of = engines is=20 on the wings and in this configuration you are 4 times more likely to = die in a=20 single engine out in a twin engine airplane than the only = engine out in a=20 single engine airplane.  With two engines the extra weight is very=20 important, which translates into extra fuel usage (also weight) as well=20 as asymmetrical thrust and human reaction issues on = failure. =20 Instead of extra reliability you actually INCREASE the odds of dying in = a fatal=20 crash by adding redundancy.
 
In electrical systems, redundancy = does make=20 great sense and is becoming the long overdue norm in certified = airplanes,=20 Diamond, Lancair, Cirrus, etc...  Two plugs, two mags, and = electrical/vac=20 redundancy has worked well in the past.  I just spent 4 hours = behind the=20 Garmin G1000 yesterday shooting 12 approaches and I will tell you that = the=20 Chelton/Garmin/Avidyne systems are amazingly less complex than the wavy = steam=20 gage needles, once you learn how to use them.  Having a reliable = approach=20 coupled to a good autopilot with great situational awareness = at all=20 times is a great example of the benefits of the advances made possible = by=20 reliable electrical system redundancy.
 
Stuart Seffern
Madison, WI
www.LantzairFlyers.com<= /DIV>
 
 
 
 
----- Original Message -----
From:=20 Timothy Spear
Sent: Monday, May 16, 2005 9:32 = PM
Subject: [LML] Airplane = Construction=20 Philosophy

Hello=20 all,

           = =20 Working in the computer field I was wondering  why so much time = in the=20 aircraft industry is concerned with minimizing the mean time between = failure=20 (MTBF) on a single component. For example in the computer field we = have moved=20 extensively to a concept called RAID (Redundant Array of Inexpensive = Disks),=20 in the =93old=94 days a mainframe disk drive with an average of a one = MTBF every=20 million hours cost tens of thousands, versus a PC drive had an MTBF of = a=20 thousand hours and sold for a few hundred. With RAID you would mirror = the data=20 between two PC drives, and the chance then of a both failing at the = same time=20 was back up to a million hours. Two PC drives would cost significantly = less=20 than the equivalent mainframe, the result is that the cost of disk = drives for=20 servers has gone down significantly. In addition, computer staff has = become=20 used to a failure mode for disk drives  resulting in reduced data = loss=20 and better recovery procedures. In the aircraft industry we have = continued to=20 engineer for the MTBF of a million hours, with two consequences. One,=20 everything is very expensive, two pilots are not used to any failures; = so when=20 a failure occurs the pilot does not know how to effectively deal with = it.=20 Therefore, why do we not accept a lower MTBF and have two complete = avionics=20 systems, fly by wire controls, engines=85. The point could continue to = everything except core structural = elements.

 

 

Tim

------=_NextPart_000_0732_01C55AE4.3F2B8FF0--