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)

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