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Date: Tue, 17 May 2005 14:36:56 -0400
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From: "Stuart Seffern" <sseffern@yahoo.com>
References: <list-946811@logan.com>
Subject: [LML] Airplane Construction Philosophy
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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

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<DIV><FONT face=3DArial size=3D2>Tim,</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>Just one problem with your theory of =
duplicative=20
redundancy in airplanes,&nbsp;engines. The common placement of =
engines&nbsp;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&nbsp;out in a=20
single engine airplane.&nbsp; With two engines the extra weight is very=20
important, which translates into extra fuel usage (also weight) as well=20
as&nbsp;asymmetrical thrust and human&nbsp;reaction issues on =
failure.&nbsp;=20
Instead of extra reliability you actually INCREASE the odds of dying in =
a fatal=20
crash by adding redundancy.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>In electrical systems,&nbsp;redundancy =
does make=20
great&nbsp;sense and is becoming the long overdue norm in certified =
airplanes,=20
Diamond, Lancair, Cirrus, etc...&nbsp; Two plugs, two mags, and =
electrical/vac=20
redundancy has worked well in the past.&nbsp; 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.&nbsp; Having a reliable =
approach=20
coupled to a&nbsp;good&nbsp;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.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>Stuart Seffern</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>Madison, WI</FONT></DIV>
<DIV><FONT face=3DArial size=3D2><A=20
href=3D"http://www.LantzairFlyers.com">www.LantzairFlyers.com</A></FONT><=
/DIV>
<DIV>&nbsp;</DIV>
<DIV>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<BLOCKQUOTE dir=3Dltr=20
style=3D"PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; =
BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
  <DIV style=3D"FONT: 10pt arial">----- Original Message ----- </DIV>
  <DIV=20
  style=3D"BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: =
black"><B>From:</B>=20
  <A title=3Dtspear@tangiblesoftware.com=20
  href=3D"mailto:tspear@tangiblesoftware.com">Timothy Spear</A> </DIV>
  <DIV style=3D"FONT: 10pt arial"><B>To:</B> <A =
title=3Dlml@lancaironline.net=20
  href=3D"mailto:lml@lancaironline.net">Lancair Mailing List</A> </DIV>
  <DIV style=3D"FONT: 10pt arial"><B>Sent:</B> Monday, May 16, 2005 9:32 =
PM</DIV>
  <DIV style=3D"FONT: 10pt arial"><B>Subject:</B> [LML] Airplane =
Construction=20
  Philosophy</DIV>
  <DIV><BR></DIV>
  <DIV class=3DSection1>
  <P class=3DMsoNormal><FONT face=3DArial size=3D2><SPAN=20
  style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial">Hello=20
  all,<o:p></o:p></SPAN></FONT></P>
  <P class=3DMsoNormal><FONT face=3DArial size=3D2><SPAN=20
  style=3D"FONT-SIZE: 10pt; FONT-FAMILY: =
Arial">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;=
=20
  Working in the computer field I was wondering &nbsp;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&nbsp; 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.<o:p></o:p></SPAN></FONT></P>
  <P class=3DMsoNormal><FONT face=3DArial size=3D2><SPAN=20
  style=3D"FONT-SIZE: 10pt; FONT-FAMILY: =
Arial"><o:p>&nbsp;</o:p></SPAN></FONT></P>
  <P class=3DMsoNormal><FONT face=3DArial size=3D2><SPAN=20
  style=3D"FONT-SIZE: 10pt; FONT-FAMILY: =
Arial"><o:p>&nbsp;</o:p></SPAN></FONT></P>
  <P class=3DMsoNormal><FONT face=3DArial size=3D2><SPAN=20
  style=3D"FONT-SIZE: 10pt; FONT-FAMILY: =
Arial">Tim<o:p></o:p></SPAN></FONT></P></DIV></BLOCKQUOTE></BODY></HTML>

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