Received-SPF: pass
 receiver=logan.com; client-ip=24.25.9.102; envelope-from=eanderson@carolina.rr.com
Message-ID: <000f01c5f944$f582ce90$2402a8c0@edward2>
From: "Ed Anderson" <eanderson@carolina.rr.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
References: <list-863209@logan.com>
Subject: Re: [FlyRotary] Re: Intersting flight
Date: Sun, 4 Dec 2005 21:38:21 -0500
MIME-Version: 1.0
Content-Type: text/plain;
	format=flowed;
	charset="iso-8859-1";
	reply-type=response
Content-Transfer-Encoding: 7bit


> al p wick wrote:
>
>>On Sun, 4 Dec 2005 14:32:10 -0500 "Ed Anderson"
>><eanderson@carolina.rr.com> writes:
>>
>>>I think the old adage KISS goes a long ways - as you know, it is
>>>
>>possible to
>>>decrease reliability (not to mention increasing weight and cost) by 
>>>increasing redundancy pass a certain point - more parts to break.
>>>
>>
>>Wow, I TOTALLY disagree with above statement. But note that I define
>>"redundant" as having independent failure odds (same as logical "or"
>>circuit). We always have risk reduction with redundancy. HUGE risk
>>reduction, because you multiply the odds. So 1 circuit has 1 in 100 odds
>>of failure. 2nd independent circuit jumps the odds to 1 in 10000! That's
>>why they run two power leads to the ECM on OEM cars. Also multiple ground
>>leads. Much much safer.
>>Perhaps you allude to cases where you add a second switch, but power has
>>to flow thru both switches for circuit to operate. In that case, yes, you
>>actually increase your risk.

You are correct, Al.   I should have been more specific, true redundancy 
does reduce the risk of failure even though you still pay the price of 
additional weight and costs.   That said, it becomes increasingly difficult 
for some of us to accurately assess true redundancy as the complexity 
(included that resulting from adding redundant circuits, components, etc) 
increases.  There is also the added element of should the redundant system 
be automatically or manually activated - each adds it's own bit of 
complexity and risk.  But, I will certainly accept the assessment of someone 
with your experience in FEMA - mine was mostly classes in school.  I still 
believe that KISS is a first principal approach, however, when the 
consequence of a failure is high, I will certainly add that "back-up" 
element to a crucial system.

Ed A