A tinkerers Toys

[HighWing]

Some kind words from you guys have prompted me to start this thread. I plan on posting some of the Modifications I have done mainly on Model IV number two, but possibly some from No. 1 also.

I welcome comments and the critiques that come to mind as well. Also if any of you have had the "Tinker" addiction prompt you to make mods, feel free to share

Since we all tend to start in the back, That will be where I will start.

Post Number 1 -
This will focus on the fairings and gap seals I put on the empennage.

I did it as well on 96KL, but this time a bit different in design. I wanted an airfoil from leading edge to trailing edge without the hour glass shape at the hinge lines. The vertical stabilizer to rudder was fairly simple as the rod end hinge design gave ample space for a complete arc on the leading edge of the rudder. The hinge at the horizontal stabilizer to elevator was the challenge due to the limited space provided by the welded tube hinge design. This required some real effort. I made up some molds to use to get several shapes I could use. Some fit as molded, some needed trimming and re working while in place to provide an unencumbered range of movemtent - both vertical and horizontal. All ribs were fabricated from 1/4" LAST-A-FOAM from ACS. After cutting, the foam was coated both sides with a medium weight fiberglass cloth and epoxy resin. After final trimming, the edges were coated with "Micro" and sanded smooth.After covering, I did riblace for reasons that will be explained later.

[airlina]

lowell, thanks for sharing your ingenuity with the rest of us. After the first installment, I can' wait to see what else you have come up with. Great job on the empennage gap seals. Bruce N199CL

[av8rps]

Ditto, ditto... !!

Keep em coming. This is some great stuff Lowell!

[Paul Z]

Lowell,

Do you have a picture of the tool to make the fiberglass fairing on the horizontal stabilizer? Very impressive and simple design to build the molds used to fabricate the gap fill parts.

Paul Zimmermann

[HighWing]

Lowell,

Do you have a picture of the tool to make the fiberglass fairing on the horizontal stabilizer? Very impressive and simple design to build the molds used to fabricate the gap fill parts.

Paul Zimmermann

The link is to one of my albums.
http://www.teamkitfox.com/Forums/album.php?albumid=474

[HighWing]

Post Number 2
Elevator trim is a must in my mind.
On my first Model IV, I ordered the Speedster Elevator and it worked well. This time elevator trim became an an add on. The first thing I did was make a trim tab by folding a piece of aluminum to the desired dimensions and shape. I wanted it to fit between the two outer welded in tubular ribs. The chord of the tab then determined the cut out dimension of the middle rib. I found that if the trailing edge is cut out first, the weld stresses would result in the hinge spar bending toward the trailing edge, so the first cut was to remove some of the #2 welded rib to clear the tab and for the welding of the square tubing. After the half inch square tube was welded in, the trailing edge could be cut out without distortion to the spar. Piano hinge was used to connect the trim tab to the square tube. The servo was attached by welding in tabs – one offset to secure the servo. The 4-40 screws were welded to the tabs to avoid the need for a wrench on top of the tab. A servo cover was made to cover the servo at the bottom of the elevator. The attachment arm for the servo at the trim tab was made by hysoling a couple of pieces of aluminum angle together to form a T, then cutting and sanding to the final shape.

With the gap seal and trim tabs, I found elevator authority a nonissue with three point landings.

As a side note, a local pilot – Avid - wanted a different profile on his elevator for additional chord and brought some drawings. I helped him with the assembly and liked the design a lot. I would be tempted to use the design if building again. Two photos are attached to give an idea of that design. The first shows the trailing edge tube and its relationship to the existing profile of the Kitfox elevator giving significant additional surface area. The second shows aweldding jig with parts in place. One thing I really liked about it is the hinge on the top surface rather than between elevator and trim tab - much simpler.

[Dave S]

Although I have never achieved the status of "tinkeringhood" that Lowell has, wanted to take Lowell's invitation to share a very small effort in that direction.

Back a while this year I decided to add a rudder trim....probably no big deal except that some of the more elegant designs that were done by builders on this list who made their modification before the fabric was on......too late for that in my case so it had to be an add on.

Here's some photos and a description of my thought processes.

1) Our friend from Oz on the list was kind enough to share what tab size and position on the rudder worked for him. Both measurements worked out perfectly.

2) Checking how simple add on rudder trim tabs are done on other aircraft, with one observation that normal certificated tube and fabric aircraft which have thick trailing edges due to the tube frame often have the tab on the right side, bent around behind the trailing edge so I decided to try that. I figure the tab is "lifting" the rudder to the right anyway and this installation allowed for less of the tab sticking out in the airstream on the left side.

3) Rather than having a sharp bend in the tab, decided to go with a curved bend which theoretically might allow for a smoother air flow over the tab.

4) In fastening the tab to the rudder I decided to go with the 3M double sided high strength trim tape....since it comes in 1/2" wide strips, it was necessary to use two strips to account for the one inch wide contact. One caveat with the adhesive method is the paint must have been prepared and applied correctly so there is no delamination of the paint layers....thought about that and it has not been a problem. Considered the traditional drill the tube and use screws; but, I like to stay away from that to avoid potential moisture penetration of the tubing.

5) The two holes in the corner of the tab are not some super-secret-vortex-generators....just a practical way to support the tab for painting before it was stuck on the plane

The last photo is looking up from the bottom to show the amount of curvature which resulted in a hands and feet off cruise.

[HighWing]

Dave,
I like your thinking. My next post will cover the very complicated rudder trim, I just had to try. More later on that.

[HighWing]

Post Number 3
Rudder trim is an often mentioned subject.
Long before the start of Model IV #2, I had fantasized on the “Wright” technique of wing warping and its possible use for rudder trim. I needed to at least try it. The plan was to make two bottom ribs out of a flexible material, tying them together and having something move the two piece bundle right or left to create an airfoil shape in the desired lift side.
One of my favorite structural materials – Carbon Fiber arrow blanks were used for the ribs. They were tied together at the cam actuators by drilling adjacent holes and using Hysol to glue in a short length of control cable across the gap. To keep the ends in place against the steel structure, I welded projections on to the tubing and threaded the ends of the carbon fiber tubes on the nubs. I also fabricated thin aluminum U channels to be glued on the outside of the tubular ribs to give a flat surface for the fabric to be glued to.
Carbon fiber tubes were also used to connect the cams needed to control the two ribs to conserve weight along with welded steel bell cranks as needed. The servo was attached in a fashion similar as that used on the elevator trim. I decided to rib lace to help support the tubular ribs as they moved against each other. For continuity, I rib laced the entire empennage.

The system works! And to answer the question, “Was it worth the effort?” I have to say yes from the tinkerer’s point of view. The idea has been put to the test and essentially put to rest. However as Dave and others will likely suggest, movable rudder trim is pretty much a nonessential item with our airplanes – sort of a set it and forget it item. Thinking about it, if I were to do the rib warp again, I would have a little hole, probably in an extension of the leading edge fiberglass, that I could insert an Allen wrench into to make fine adjustments and save the weight and complexity of the electric servo.

The last two pictures show the relative curvatures of the two sides needed for the same result Dave and many others have gotten with a simple tab. I do like the clean, though

[n85ae]

Nice stuff here Lowell! I like what I see,

Jeff