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Thread: A tinkerers Toys

  1. #11
    Senior Member HighWing's Avatar
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    Default Re: A tinkerers Toys

    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.
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    Lowell Fitt
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  2. #12
    PNWJARED's Avatar
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    Default Re: A tinkerers Toys

    HighWing

    Excellent Post. Very Clean! Very Cool! way to up the bar for the rest of us!

    I assume the results are evident as well.
    Kitfox 7-Flying
    ABW 26", T3, ABW 3200 Tailwheel
    Rotax 912ULS, Warp Drive Taper

  3. #13
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    Default Re: A tinkerers Toys

    Post Number 5.
    When I began this project, there was an article in Kitplanes by the electronics guru, Jim Weir. In it he explained the electrical needs of LED bulbs and explained that for constant light output they needed constant current rather than a set voltage. He then offered a power supply in schematic form. I was hooked. When I finished my first one, I was surprised how large it was. Later experience with DC to DC voltage converters proved the concept. To change from 12 V. to the voltage needed for a typical LED required first conversion to AC to feed a transformer, then back to DC at the new voltage. Without adequate filtering, these can be really noisy. Flying under Sport Pilot, I really didn’t need the lights, but wanted them just in case.
    The first pictures will show how I mounted the aft position lights. To avoid complexity, at least so I thought, I decided to position them on both sides of the rudder so there wouldn’t be a possibility of rudder shadowing. For that I needed some custom lenses. The lenses were made using a vacuum forming technique I learned in the dental office – Mouth guards and bleaching trays. No longer having the equipment, but knowing how it worked meant searching for components and building my own.

    The lights on the wing tips used the same mounting method that I used on 96KL, but using the LEDs rather than the big bulbs. While working at United Airlines as a fueler, I noticed on the B-727s they had an interesting wing tip design that I adapted to the Kitfox. A “door” was cut out of the fiberglass. Then a lip was added to provide positive positioning with screws into nut plates for attachment. A lens was fabricated using heated Lexan forced over a plug made from the wing tip for shape. This was then glued to the “door”. A note on heat forming Lexan (Polycarbonate). A quirk of the material is that it is extremely hydrophilic – it absorbs significant quantities of water. To heat form it successfully, it needs to be dried in an oven for a time determined by its thickness. Otherwise it will look really interesting after forming - lots of steam bubbles within the plastic - large and small.
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  4. #14
    Senior Member jrevens's Avatar
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    Default Re: A tinkerers Toys

    As usual, really excellent, Lowell! You're a man after my own heart, but you are the king of innovation, making your own tooling, etc., etc.!! I love seeing what you have done!
    John Evens
    Arvada, CO
    Kitfox SS7 N27JE
    EAA Lifetime
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  5. #15
    Senior Member HighWing's Avatar
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    Post Number 6 Landing Gear

    The landing gear came as a suggestion from a friend. He gave me some numbers and that became the goal – two inches taller at the firewall and 70 inches beween the brake mounting pads. To ensure the same fore aft relation with the new gear legs as the original bungee gear, it was important that the axles be exactly under the same point on the airframe so that was the first goal. The fuselage was positioned in three point the tail supported by the tail wheel and a support frame forward that held the bungee gear with the axles where they would be if in the wheels. A rail like structure was made as precisely as possible using inverted angle iron and it was fixed to the floor perpendicular to the long axis of the fuselage with Bondo. “A” frames with inverted Vs as feet to slide on the rails provided the means for adjusting the width of the gear legs with no fore and aft deviation and removable supports that fit into the inverted Vs provided the means to increase the gear leg lengths as desired. The A frame adjustment support dimensions were determined to get the desired 2” additional height at the firewall - increased leg length when removed. Then it was a matter of creating landing gear weldments that closed the gap between the axle mounted on the A frames and the gear leg attachments on the bottom of the fuselage. These weldments became the landing gear legs the spring struts and the cabane. The fairings were of thin aluminum to conserve weight.

    A note: with the desire for accuracy, great care was taken to ensure proper tracking if wheels were on the axles. It was found, as many suggest, that the original gear (1992) was significantly toed in and appropriate adjustments were made to correct that.
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  6. #16
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    Post number 7 Baggage Area, Hat Rack, Shoulder Harness Attach Points

    The baggage area is another topic that comes up a lot. Most of the talk is increasing capacity. My goals included that as well as reducing weight and improving accessibility. The floor was made up of Fiberglass with foam strips within the plies to add stiffness. Aluminum angles with slots were then riveted to the outer edges. The slots were to accommodate Velcro straps that would secure the sides to the floor. Also at four points are loops to anchor a net to secure the contents. Small aluminum panels are riveted to the floor on each side to prevent the sack contents from interfering with the flaperon control horns.

    On my first Model IV, I was never comfortable with the shoulder harness attachment points. To keep the right harness on my shoulder, I made a strap that held the right and left straps together when I flew. Modifying that original design became a major focus as I followed the lead of some friends who were modifying the hat rack area during Model IV builds. One of them simply cut out the bracing in the Hat Rack area behind the seats for easier access to the baggage area. My choice was to cut it out as well, but then replacing it with the bracing design found in the skylight area between the wing spar carry through tubes. For the shoulder harness attachments, tabs were welded exactly between the shoulders of both passenger and pilot, then steel tubes were welded between those points and the corners at the aft edges of the turtle deck for strength.
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    Lowell Fitt
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  7. #17
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    Default Re: A tinkerers Toys

    Post Number 8 Engine Mount

    When I did the W/B on my first.IV I found that I was forced to plackard my baggage capacity at 25 lbs. max. This was because of what I had done to the tail airfoils and fairings. Some calculations suggested I could recoup that on the new airplane by moving the engine forward a couple of inches. That and the long held wish of having the ignition modules hard mounted to the firewall half of the engine mount and the oil tank in a better location pushed me to build my own mount. A ring mount that fit the rear of the engine was made first. Then with that mounted to the rear of the engine, the engine was positioned in front of the fuselage on an engine stand in the desired position, and once again, the gap was closed with a welded tube structure. It was found that Kitfox used no thrust offset so the engine was placed in line with the longitudinal access of the fuselage. To determine the thrust line, a photo was taken of a friend’s Model IV as near to the level of the thrust line as I could. Using horizontal and vertical lines available in the editing program, the image was rotated until the prop blades were perfectly vertical which gave the correct horizontal of the thrust line as related to the fuselage. Lines were drawn on the photo to calculates dimensions from known landmarks.

    The rubber isolators were made of a two part Urethane RTV cast in molds made of Delrin.

    The only issue I discovered, was when fitting the cowl, it was found that the cowl contour drifted toward the centerline earlier than I thought and a modification was necessary for the cowl to clear the bottom of the oil tank. With my first Kitfox, I had noticed that the oil tank had several dents on the lower edge. It appeared that the stainless steel was soft, so tapping with a hammer created a dent that allowed for a quarter inch clearance at the bottom. I didn’t like the hammered look, so covered it with Micro and sanded it smooth. I didn’t like the look of the micro and this is the primary reason for the painted oil tank. The ignition coils fit as planned.
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    Lowell Fitt
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  8. #18
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    Default Re: A tinkerers Toys

    Wow Lowell, you are a real craftsman! I would say that what you've shown us is a bit more than tinkering. :-) Maybe more like: an artist at work. JImChuk

  9. #19
    Senior Member jrevens's Avatar
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    Default Re: A tinkerers Toys

    That's all very cool, Lowell! Your mold for the engine mount isolators brought back memories of similar experimentation. Made a mold of aluminum to form urethane tailwheel tires for a Scott tailwheel, with the thought that they would last "forever" - or at least longer than the store-bought ones. The problem with the particular compound of urethane, soft enough to be similar to the factory made tires, was that it would take a set after sitting on the ground for awhile, creating a flat spot until it finally recovered. The "thump, thump, thump" when taxiing (especially in cold weather) drove me crazy. It was a fun project though.
    John Evens
    Arvada, CO
    Kitfox SS7 N27JE
    EAA Lifetime
    Chap. 43 honorary Lifetime

  10. #20
    Senior Member HighWing's Avatar
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    Default Re: A tinkerers Toys

    Thanks, Jim.
    Thinking about your post almost all day, lots of things came to mind. I think one thing I will claim and that is a level of perseverance. I always tell people to check my garbage can. Eventually the project will come out close enough.
    Lowell Fitt
    Goodyear, AZ


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