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Thread: New trim lever

  1. #1
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    Default New trim lever

    Hi guys, I've been flying my Kitfox 4 with 912 as often as I can, and wanted to do something with the elevator trim for landing purposes. I have the Ray Allen servo, and a trim tab I installed when I rebuilt the plane. If I don't use trim for landing, I tend to come in faster then needed, and float quite a bit further down the runway. I've been using the electric trim, but it's very slow, maybe 20 seconds to go from neutral to full trim. And then back again before takeoff. I took a bungee and ran it around the seat truss and joy stick, and made a notched piece of aluminum for keeping the bungee where I wanted it for faster trim. That did work, but was kind of clumsy and so I tried another way of tightening the bungee. This is what I came up with. And it does really work well. Takes nothing to pull the lever back, and it trims the stick to where ever you want it for you approach. Some leather between the moving parts for friction. Now I use the electric trim for cruise and this for landing. If the tension is set right, when you push the stick way forward, the trim lever moves and the trim is removed. This was the proto type, and looks a bit clunky, When we ramp up full time production, we will make it shine. Just kidding, no production planned. Anyway, laugh if you like, or copy it if you want to. This would probably work for some one with no trim tab as well as long as you only need nose up trim. JImChuk
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  2. #2
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    Default Re: New trim lever

    WARNING! WARNING! WARNING. This afternoon I went for a flight and on my second landing when I was slowing up and started to raise the nose, the elevator was jammed. I think it was my trim lever was pulled back to far, and the arm that pulls on the bungee cord was hitting the seat. I jerked the stick side ways and back and on about the fourth try, it let loose. I think I had forward stick, but was afraid to use it if I Iost the neutral elevator position I was able to have. I'm going to make a stop that will limit the travel of the trim lever so that can't happen again. I'm also going to take everything apart from stick to elevator to make sure it wasn't something else. A half hour before this, I had landed at a friends grass strip, and forgot to move the trim lever back to normal flight after landing with it in trim mode. When I took off, it started to climb to much, and I right away pushed the trim to neutral setting. I probably pushed it way further then normal and set myself up for the exciting finish of the flight. It all ended ok, but was hairy for a bit. So if anyone liked my trim system and want to copy it, make sure you have some kind of stop to keep it from jambing the controls.

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  3. #3

    Join Date
    Dec 2019
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    Idaho
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    Default Re: New trim lever

    20 seconds to adjust trim sounds like a really long time. Could there be something wrong with the trim control motor/mechanism? I'd
    rather get that working than the solution you built. Anything that can get in the way of the stick seems like an accident waiting to
    happen.
    Building SS7
    915iS
    Garmin G3x

  4. #4
    Senior Member 109JB's Avatar
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    Morris, IL
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    Default Re: New trim lever

    Yank the electric servo and run a 1/4 turn locking push-pull cable to the tab. That is how my Sonerai is rigged and going from neutral to either stop is as fast as you can push or pull the cable. It works very smoothly and once you get used to it you just know where it needs to be for the most common flight configurations.
    John Brannen
    Morris, IL
    Sonerai IIL (Single Seat)
    Kitfox 3/4 1050 - Rotax 582 (Back Flying and sold)
    Kitfox IV 1050 - Rotax 582 (sold)
    Kitfox IV 1200 Speedster - Rotax 912 UL (project)
    Piper Twin Comanche (Sold)
    Glasair 1 FT (Waiting to start)

  5. #5
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    wales,ny
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    Default Re: New trim lever

    Quote Originally Posted by VictorV View Post
    20 seconds to adjust trim sounds like a really long time. Could there be something wrong with the trim control motor/mechanism? I'd
    rather get that working than the solution you built. Anything that can get in the way of the stick seems like an accident waiting to
    happen.
    Jim , I gotta agree with Victor here, too much going on on your what should be your primary flight control , your control stick. Some other solution with a secondary control not on the stick should be your answer. Glad you and the airplane survived this "learning experience" unscathed Bruce N199CL

  6. #6
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    Default Re: New trim lever

    Thanks for the replys everyone. As far as a trim cable, I have one on my Avid Flyer, and had the cable break off once. It would bend a bit each time it was used and eventually got brittle and cracked. A trim tab will flap up and down if not connected, and that was an exciting experience as well. Talk about a stick shaker. I really do like the trim adjust I made, but should have put stops on it right away.

  7. #7
    Senior Member 109JB's Avatar
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    Default Re: New trim lever

    If flexing broke the cable, one of 2 things happened. First it was a cheap cable. Second the sheath was attached too close to the bellcrank on the trim tab. In either case it was a design flaw, not a cable problem. On my Sonerai the cable wire is 0.085" diameter, not the 1/16" most cheaper cables come with. You can even get thicker than that. I got mine at McMaster Carr. Push-pull cables are used for primary controls on many ultralights, are used for the controls on the Velocity aircraft, and are used to retract landing gear on some Pipers. A properly designed and maintained push pull cable system will not break.
    John Brannen
    Morris, IL
    Sonerai IIL (Single Seat)
    Kitfox 3/4 1050 - Rotax 582 (Back Flying and sold)
    Kitfox IV 1050 - Rotax 582 (sold)
    Kitfox IV 1200 Speedster - Rotax 912 UL (project)
    Piper Twin Comanche (Sold)
    Glasair 1 FT (Waiting to start)

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