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REFLECTOR: Re: Main Gear Position Switches
In an effort to adhere to the K.I.S. principle (Keep it simple) I use a single
microswitch under the pilots side overcenter linkage to detect the "Up and
Locked" state of the main gear. While separate switches for each gear leg is
perfectly fine, it does add components and wiring requirements over and above
what is actually needed.
With the gear retracted and the main gear cables adjusted properly, the inside
angle of the inverted "V" formed by the main gear overcenter linkage should
remain constant while the gear is "Up and Locked". If either side (or both
sides) should start to drop the angle will increase.
Mount your microswitch on an aluminum bracket so that the "arm" of the switch
is away from the base of the angle. With the gear in the "Up and Locked"
position, slide this assembly up between the angle formed by the linkage until
you just hear the switch 'click' (make). Mark the position of the bracket
carefully on the linkage. You must now attach this bracket to the linkage in
the exact same spot as you just marked. I attach my switch bracket with a "V"
pattern of 1/8" pop rivets with the two of three rivets located closer to the
side that the switch is mounted on. NOTE: I remove the switch from the bracket
to properly install the rivets.
My wiring for both the gear "Down and Locked" switch and the "Up and Locked"
switch gets routed across the top of the carry through spar to the middle of
the airframe. With the gear in the "Down and Locked" position, I then let the
harness form a very comfortable "J" and attach the loose end with a tywrap to
the pilots side of the linkage close to the "Down and Locked" switch. From the
tywrap, 3-4" of wiring is all that is needed for the connections to the "Down
and Locked" switch to be made comfortably. Attach the remaining wiring going
to the "Up and Locked" switch to the linkage with a tywrap near the bracket
location for the "Up and Locked" switch.
During the operation of the gear, there should be no tight bending or pulling
of the wiring, just a smooth, slow 'rotation' in the loop at the bottom of the
"J". Any concerns about this harness getting caught on anything during the
retraction / extension process should be alleviated once you see the operation
As always, Safe and Speedy Construction!