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.
Here you can see some of the basics: 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 window
hinge half. 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 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 you see the pivot tube from the pilot's side,
along with the tabs that locate the windshield brace tube, and
the tabs which retain the upper rear of the windshield. On the
outside of the windshield (utilizing the same tabs) are aluminum
angle/vortex generators which act as brackets for retaining the
piano hinge which is used to attach the Lexan for the upper rear
fuselage or turtleback. The vortex generators apparently work,
as the turtleback bows upward when flying without the rear side
windows. Must be some lift there somewhere... The turtleback also
has piano hinge along each upper side to attach it to the rear
side windows, the lower edge of which fits into a slotted aluminum
track along the upper fuselage sides. The rear side windows can
be removed in about 2 minutes, and stowed in the cargo area behind
the seats. The whole Lexan rear window assembly can be removed
in about 4 minutes, making the airplane entirely open in back.
Here is what it looks like from behind the vertical
tube, you can see how the piano hinge is used to attach the upper
rear Lexan, and then the side Lexan window has it's own piano
hinge to lock the two together. By pulling the hinge pins, the
whole assembly is easily removed. You can also see the control
arm with the flap pull tube attached.
Here is another picture of it from the outside.
(The blue thingy is my wife's headrest)