Message-ID: <37AC7C9B.543B3C6@mc.net>
Date: Sat, 07 Aug 1999 13:36:11 -0500
From: jerry@mc.net
Reply-To: jerry@mc.net
To: Lancair Mail List <lancair.list@olsusa.com>
Subject: Re: New Pre-Flight Item
References: <fb8a1f51.24daf30f@cs.com>
Mime-Version: 1.0

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For Rick Argente et al

My 320 will not have micro switches for the gear over center links
position.  I'm going to Radio Shack and purchase "normally open" reed
switches which are closed when in close proximity to magnets.  These
will be placed in or close to the drag link operating mechanism.  When
the drag links are fully locked over center the magnet will close the
reed switch giving a green light.  This can be done without the wires
moving with the movement of the drag link.

My plan is to mount the switch into one of the lightening holes of
GM4.  It will be mounted in an adjustable eccentric so as to align
with the magnet fastened to the over center link.  When the over
center link is just coming home and firmly locked the reed switch will
be just coming closed.

This same switch can be used to show the nose gear in the down and
locked position with no wires, at all, inside the nose tunnel.  This
avoids  all the fury that goes on in there....I read where one
builder/pilot had a bird strike to his nose micro switch and it failed
to show safe gear.  One could mount the reed switch in the nose tunnel
glass/foam on an adjustable mounting pad of phenolic.  This would go
on the right side of the tunnel inside the cockpit.  The magnet would
be mounted on the tab arm of GM27.  Adjusted so that as the over
center just comes home and locked the switch makes and turns on the
green light.

The switch/magnet method is clean, sophisticated, less vulnerable to
the elements of dirt oil and grease, adjustable, cheap, allows builder
creativity.  You can also place another reed switch along side this
switch.  The second switch would be the "normally closed" type and
opened when in the influence of a magnet.  This second switch would
light a "gear in transit light".  The intransit light would confirm
gear down by going out when the over center link locks.  So if the
green light burns out you would still have confirm of gear reaching
the over center position.

These little Radio Shack switches are good for many things in the
build of our airplanes.  They are manufactured to accommodate the home
security system installations.  So the switches are plentiful and
cheap.  They are also sealed with silicone stuff to keep the elements
out and come with two wires potted into the switch housing.

Boeing uses super sophisticated magnetic switches for all kinds of
stuff.  A partial list is..... to show the gear up and down, to tell
the computers managing airplane systems that the airplane is on the
ground or in the air.  We could use these for flap positions, trim
position, gear door position, They have been used in measuring fuel
levels in a cheap/easy to build standpipe systems.  Your imagination
is the only limit.  Good luck and have fun with reed switches.

Jerry Grimmonpre'

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