A tinkerers Toys

[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

[HighWing]

Post Number 4
A buddies 604 lb. empty weight Model IV was in the back of my mind during my entire build. With all the gadgets I was putting on my airframe, I wanted to subtract some weight. I had heard that the extruded PVC lift strut fairings could add up to 14 lbs. so thought of ways to possibly reduce that. At one of the factory fly-ins, I saw Dan Denney’s highly modified Kitfox and noticed that he had aluminum fairings, so that became my challenge. Then watching a neighbor having a new roof put on with the gutters rolled from a coil of sheet aluminum established my goal. I started working on a rolling mill.

My first goal was to roll a sharp angle at the trailing edge to capture the free trailing edge to avoid what happens sometimes with the aluminum flaperon. Sadly, that is about as far as I got as personal pressures wanted the airplane flying. After rolling a section I used a brake to fold an angle mid span on the aluminum and after folding, that became my airfoil. My shear and brake only had a 30 inch capacity, so there needed to be four lengths of fairing for each section of lift strut – sixteen in all. One thing became clear early that presented an unexpected challenge. When a section of the fairing was folded, being held together with the angled trailing edge, it was not stable. It could be twisted into a near helix just by rotating leading edge against trailing edge. If not careful, this could result in a twist on the fairings. The PVC sections being long enough to cover the entire span avoided this problem, but it still was a slight possibility if not checked carefully. The solution was to glue one length together with great care, ensuring it being perfectly straight. Then an assembly jig was made from that section. This also provided an unexpected benefit – mentioned later. To hold the fairing in place on the lift strut foam spacers were cut using a home made punch.

The lift strut was supported vertically, Wing end down. A section of aluminum fairing was placed over the lift strut and held in place with a complete section of foam at the bottom end, then the clamping fixture was placed and clamped to secure the partial foam section against the strut on the upper end. A 1 oz. mix of twopart Urethane foam was then poured into the fairing shape and allowed to cure. The clamping fixture was then moved to the next location and the process was repeated. I had learned that the Urethane foam was very adhesive and found no need to add adhesive to the aft joint. The benefit of using the clamping jig was when I made sure that each joint between fairing sections had the clamping fixture overlapping to help form a smooth joint. Once complete, the trim to allow for wing folding was accomplished and the V connection covered with a small fiberglass section faired with Micro. The final finishing touch was to form and glue on thin sections of aluminum to cover the joints between sections. The aluminum I used was .010 thick. Early I felt the need to placard with a NO PUSH decal, but decided it was not necessary as the Urethane foam gives a really firm feel to the fairings. Before and after weights indicated that the fairings were very close to 5lbs. total.

[Bluebird19kf]

Hey highwing, how does the hinge work on your aluminum trim tab on page 4. Is the one picture (with it uncovered) showing the servo and tab installed in full down position? It would seem you would have very little or now down and a lot of up movement available do to the hinge being fully closed. Did you mount your square hinge attach bar rotated slightly down to get some down movement? Also is this the hinge that is used in this.

http://www.aircraftspruce.com/catalo...pianohinge.php

Spuce # 03-00052-3

Thanks

[HighWing]

Hey highwing...

super busy today and out of the area tomorrow - 60th HS reunion. Will respond in full Thursday.

[HighWing]

The aluminum tab used was formed to the shape pictured. This gives a profile that allows for the full range of motion of the servo - up and down. Regarding the hinge. What I used is not the hinge in the link. I did find the description of what I used lower on the page -

MS20001P aluminum hinge is extruded. The closed hinge loops cannot be pulled apart. Furnished with hinge pin. Anodized finish.

But or some reason, I couldn't find it as an order item.