Return-Path: Sender: (Marvin Kaye) To: lml Date: Fri, 18 Jul 2003 15:34:58 -0400 Message-ID: X-Original-Return-Path: Received: from tomts15-srv.bellnexxia.net ([209.226.175.3] verified) by logan.com (CommuniGate Pro SMTP 4.1b9) with ESMTP id 2478944 for lml@lancaironline.net; Fri, 18 Jul 2003 15:22:43 -0400 Received: from starband.net ([65.92.21.18]) by tomts15-srv.bellnexxia.net (InterMail vM.5.01.05.32 201-253-122-126-132-20030307) with ESMTP id <20030718192241.OQRU21221.tomts15-srv.bellnexxia.net@starband.net> for ; Fri, 18 Jul 2003 15:22:41 -0400 X-Original-Message-ID: <3F1848D6.6040009@starband.net> X-Original-Date: Fri, 18 Jul 2003 12:21:58 -0700 From: Hamid Wasti User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.4) Gecko/20030624 Netscape/7.1 (ax) X-Accept-Language: en-us, en MIME-Version: 1.0 X-Original-To: Lancair Mailing List Subject: Re: [LML] Re: Essential Buss versus Fuel Endurance References: In-Reply-To: Content-Type: multipart/alternative; boundary="------------040606070600080800040302" This is a multi-part message in MIME format. --------------040606070600080800040302 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Shannon Knoepflein wrote: >....like to continue this discussion and keep it grounded >(pun intended) in physics, then by all means let's do it....maybe we'll >all learn something from it. > Rather than keeping the discussion restricted to only theoretical physics, let me include the realm of reality into it. If you KNOW FOR SURE that the only thing that has gone wrong is a dead alternator and nothing else is affected, then continuing the flight, in fact continuing operations till you get back to the home base several flight segments later is not a problem. However, the reality is that you don't know what has gone wrong and why. Did the alternator suffer a catastrophic failure and has damaged other things as well? Did the alternator fail because of excessive load (a resistive short in the system) and the other alternator and the batteries are about to follow in short order? Are there any other secondary failure modes that have compromised the system? Is the apparent failure of the alternator in reality some other failure of the electrical system? Did you learn about the failure when it happened, or are you becoming aware of it when the battery started to get almost drained? In a perfect world you will know the answers to all those questions and will make an informed decision about whether to continue the flight or to land soon. In the real world, you will have to guess, which brings me to the next point. >Sorry, you calling me a "punk" certainly doesn't prove anything. > The choice of the phrase from a classic movie, while amusing, could be considered inappropriate. However, the gist of the message was on point: You are counting on your luck when you press on after an APPARENT failure of an alternator by ASSUMING that everything else is fine. On a slightly unrelated note, let me expand on the term "resistive short" used above. I came up with that term to differentiate from a "dead short" which is a short between two wires with a very low resistance (almost zero). I have come up with the non-standard term "resistive short" to describe a short where there is some small but consequential resistance between the two wires. This could be a 0.5 ohm short between the 12V and ground. It will conduct 24A and generate 288W of heating. In some instances a resistive short can be a worse condition than a dead short, especially when we have not thought about it and included it in our design. The good news is that a resistive short is fairly hard to create and hence rarely encountered in real life. The bad news is that it is most likely to happen as a secondary failure after something else (like and alternator) fails. Hamid --------------040606070600080800040302 Content-Type: text/html; charset=us-ascii Content-Transfer-Encoding: 7bit Shannon Knoepflein wrote:
....like to continue this discussion and keep it grounded
(pun intended) in physics, then by all means let's do it....maybe we'll
all learn something from it.
Rather than keeping the discussion restricted to only theoretical physics, let me include the realm of reality into it.

If you KNOW FOR SURE that the only thing that has gone wrong is a dead alternator and nothing else is affected, then continuing the flight, in fact continuing operations till you get back to the home base several flight segments later is not a problem.  However, the reality is that you don't know what has gone wrong and why.  Did the alternator suffer a catastrophic failure and has damaged other things as well?  Did the alternator fail because of excessive load (a resistive short in the system) and the other alternator and the batteries are about to follow in short order?  Are there any other secondary failure modes that have compromised the system?  Is the apparent failure of the alternator in reality some other failure of the electrical system?  Did you learn about the failure when it happened, or are you becoming aware of it when the battery started to get almost drained?

In a perfect world you will know the answers to all those questions and will make an informed decision about whether to continue the flight or to land soon.  In the real world, you will have to guess, which brings me to the next point.
Sorry, you calling me a "punk" certainly doesn't prove anything.
The choice of the phrase from a classic movie, while amusing, could be considered inappropriate.  However, the gist of the message was on point: You are counting on your luck when you press on after an APPARENT failure of an alternator by ASSUMING that everything else is fine.

On a slightly unrelated note, let me expand on the term "resistive short" used above.  I came up with that term to differentiate from a "dead short" which is a short between two wires with a very low resistance (almost zero).  I have come up with the non-standard term "resistive short" to describe a short where there is some small but consequential resistance between the two wires.  This could be a 0.5 ohm short between the 12V and ground.  It will conduct 24A and generate 288W of heating.  In some instances a resistive short can be a worse condition than a dead short, especially when we have not thought about it and included it in our design.  The good news is that a resistive short is fairly hard to create and hence rarely encountered in real life.  The bad news is that it is most likely to happen as a secondary failure after something else (like and alternator) fails.

Hamid
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