Match: 
#3
Message: 
#20265
Date: 
Oct 07, 2004
From: 
"Robert L. Nuckolls, III" <b.nuckolls(at)cox.net>
Subject: 
Re: Horizontal contactor



The contactor orientation issues came to a boil more than 10 years
ago when some airshow performer landing and discovered a trashed
starter and chewed up ring gear. Theory was at the time that g-loads
during the show teased the contactor shut and welded it.

In all likelihood, the performer was concentrating on the task
ahead and did not notice that the starter contactor stuck when
the engine was started . . . he probably flew the whole event
with the starter motor engaged.

Let's noodle through how these things work:

The battery contactor has a fairly light spring and yeah,
one MIGHT be able to tease an OPEN contactor CLOSED with
g-loading . . . but we fly with this contactor already
engaged. You're NOT going to drive it OPEN with g-loading.

Starter contactors have much heavier springs (for the express
purpose of driving contacts open even when they may have stuck
a little bit). Starter contactors usually mount on the firwall
with their axis of operation parallel to waterlines. Not only
is the starter contactor relatively immune from effects of
g-loading due to much heavier spring, it's mounted in the
airplane such that it doesn't experience g-loads due to
aero-maneuvers.

Consider further that many folks don't have battery boxes.
The battery sets in a shallow tray on a horizontal shelf.
There are no vertical surfaces upon which one might mount
the battery contactor . . . I sure wouldn't build a bracket
for the sole purpose of standing the battery contactor up.
That puppy lays down on the shelf right beside the battery.

Is there an "ideal" mounting position? Perhaps for the
battery contactor . . . a vertical mounting with the business
end down will have a very small operating benefit. The greater
benefit is to gather condensate in the lid away from the
contacts. I might even drill a #40 drain hole in the lowest
part of the lid.

I'll suggest that 99% of the worrying about contactor
orientation adds no real value and will at best influence
service life by perhaps +/- ten percent. Since we're
designing failure tolerant systems from the get-go,
I wouldn't loose any sleep over contactor service life.

Bob . . .


>
>
>In a message dated 10/7/2004 1:27:40 PM Central Standard Time,
>mick-matronics(at)rv8.ch writes:
>
>Hi  Bob,
>
>You may want to update the B&C guys on this issue,
>since I  asked them this question a couple of hours
>ago, and they said that I should  mount the contactor
>vertically.
>
>I didn't like the answer, so I  searched through the
>archives, and found this Q&A.  I'm happy to  hear
>they don't have to be  vertical!
>
>Mickey
>
>
>Good Afternoon Mickey,
>
>For What It Is Worth.  I had an Essex 8449 contactor in service for  about
>twelve years that I had mounted with the coil horizontal. It started 
>to  become
>intermittent.  I contacted the manufacturer and asked about the old  mounting
>rumor.  I was told that it should have been mounted with the coil  vertical
>and the business end down.  I switched to that when I replaced the  contactor
>about three years ago.  So far so good, but who knows for  real?
>
>I had about two thousand hours of flight time with the coil  horizontal.
>
>Happy  Skies,
>
>Old Bob
>AKA
>Bob Siegfried
>Ancient Aviator
>Stearman  N3977A
>Brookeridge Airpark LL22
>Downers Grove, IL 60516
>630  985-8502
>
>
>---


        Bob . . .


      --------------------------------------------------------
      < Throughout history, poverty is the normal condition  >
      < of man. Advances which permit this norm to be        >
      < exceeded -- here and there, now and then -- are the  >
      < work of an extremely small minority, frequently      >
      < despised, often condemned, and almost always opposed >
      < by all right-thinking people. Whenever this tiny     >
      < minority is kept from creating, or (as sometimes     >
      < happens) is driven out of a society, the people      >
      < then slip back into abject poverty.                  >
      <                                                      >
      < This is known as "bad luck".                         >
      <                                    -Lazarus Long-    >
      <------------------------------------------------------>
                   http://www.aeroelectric.com


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#3 

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