Fine Tuning the Flaps
One of the biggest challenges to getting better
airflow over the top of the windshield and under the wing was
the position of the flap actuating rod. It was in the way of good
airflow, and I wanted that area free of any non structural obstructions.
So I moved it down, flipped the control horns over, and made it
direct actuating without any linkage.
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Here you can see some of the basics: (Picture on
the right & the next two lower ones are from a couple years
ago) There is now a 5/8" x .028 4130 tube that is welded
to the uprights and diagonals and extends from the outside of
the airplane almost to the middle of the airplane, one tube on
each side. The flap actuating rod runs through this. It is a length
of 1/2" x .058 4130. The tube has a number of tabs welded
to it that extend ahead of it, this is to attach the windshield
and the rear cabin top. You can also see an aluminum u-channel
attached to the rear of the vertical upright, this is what the
front edge of the rear side sliding window fits into.
The flap
lever itself was welded to the rod and gusseted, everything was
assembled and then the tubes were welded to the uprights, so there
was little margin for error. The lever is just to the passenger
side of the center upright. I replaced the original 3 position
slider/locator detent piece with a new strip that allows me a
number of positioning options for the flaps, they can be down,
normal, or reflexed, depending on whether I am solo or carrying
a passenger. This helps the trim situation more than you could
imagine. The MKIII responds quickly to trim inputs from the flaps.
Lowering the flaps causes the airplane to nose down, as the center
of pressure on the wing moves aft as the airfoil changes, and
raising (reflexing) the flaps causes it to nose up as the center
of pressure on the wing moves forward. The flap handle now has
a small bushing welded into it, and a roll pin driven into the
bushing. The roll pin fits into the holes in the strap similarly
to how the original positioner worked, however it is now possible
to have three holes quite close together at the up position to
fine tune the airplane's pitch trim. There are seven holes total,
the top three for trimming the airplane, only the bottom four
actually lower the flaps to any extent. The handle is longer than
originally, as there was not enough leverage with the original
length of handle to get that last position for about 35 degrees
of flaps.
I cut the whole original assembly off with a Moto-Tool
and rewelded it about five inches down from the wing, and then
fabricated a locator strap separately and bolted it in position,
it was easier to get everything to line up that way.
Here's how it looks with the new cabin top in place.
