Trim Tabs & Wheel Pants


Below is the aileron trim tab. It is adjustable by loosening the wing nut and sliding the wire pushrod. The wire is a looped oval, and passes under a flat washer and wing nut. The wing nut is secured by a safety ring & clip looped through the wire. The trim tab is not rigidly attached to the trailing edge but is hinged with large RC model airplane nylon hinges to eliminate stress on the Lexan. The wire pushrod, nylon clevis, and control horn are all RC model airplane items. There is a 1/4" aluminum tube riveted to the tab to keep it from twisting. The tab gets adjusted down for flying solo, and adjusted up level when carrying a passenger. But if you forget, it is just a minor nuisance for that flight.


Below left is the rudder tab. It is fixed, & about two rib bays long. The attaching rivets do not go into the trailing edge, but into the curved rear portions of the ribs, where they attach to the trailing edge. Just below the trim tab is the rear nav light. BAD MISTAKE. Put it somewhere else. Excess weight on the trailing edge of a MKIII rudder will cause rudder flutter when you relax pressure on the rudder pedals, which will then cause you to need a rudder counterweight, on the right.

My fix was to make up a counterbalance from a 19" long 1/2" 4130 tube welded to the top of a 3/4" 4130 tube which fits down into the front rudder spar. The front half of the counterbalance was made from available scrap, including iron (heavy) water pipe. Added oversleeves of pipe until the wobblies went away. Since the rudder on 20P was non standard & squared off, (like the rest of the MKIII) the task was simplified. If the rudder had had the standard curved top, adding the counterbalance would have been more challenging. I suspect the ideal way to balance the rudder would be after painting it, but before installation on the aircraft. Then you could lay it over sideways, arrange to pivot it on the hinge pin, and adjust the rod weight until it became level.


If you have never seen how wheel pants get mounted to the landing gear, it's pretty easy. My method is not at all original, I learned it out of Tony Bingelis' book; "The Sportplane Builder", an excellent resource. The picture to the left shows how to modify the axle nut: Take a flat washer with a 5/16" or 3/8" hole and weld an AN-4 nut to the inside. Weld the washer to a length of 1" steel tubing, and then weld the tubing to the top of the castellations of the axle nut. (Leave the slots open for the cotter pin) Weld it true, or the mounting point moves when the nut is adjusted. The real trick is figuring how long to make the steel tubing. Mine is 2 3/8" from the washer face to the outer edge of the castellated axle nut, but that will vary depending on brakes, non standard wheel bearings, spacers, type of wheel pant, etc. Note the balance weight: stops wheel shake just after takeoff.

The inside wheel pant bracket is made by taking two 1" X 1" aluminum angles, overlapping them, and riveting them together. Then bolt one to the brake backing plate, and the other gets two AN-3 blind nuts riveted on the wheel side, for the AN-3 bolts that go through the fender and hold it in place. Not shown, but a good idea, is adding metal doublers epoxied to the inside of the wheel pant to reinforce the fiberglass in the bracket area.

These pictures depict the Kolb aluminum gear legs and axle brackets. I am no longer using this gear, or wheel pants, but the basics typically stay the same.


Gullwing Doors

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