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  1. #1
    H5487's Avatar
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    Need help with lightweight twin rudder linkage

    Howdy Guys,

    I picked up a BMJR Twin Lizzie with the intention of installing a small electric motor and RC gear. The Lizzie has only a 30" span and is designed for .020-.049 power so building light is important. Because this model was originally designed for free-flight, the plans don't show how to build movable rudders. So, I've got a couple of questions for y'all...

    1. Since the rudders are not on the fuselage centerline, a belcrank will be necessary. What would be the lightest setup for rudder control?

    2. To save complexity and its accompanying weight, can I get by with only one moveable rudder or do I really need both?

    The plane won't be built for aerobatics; just a nice little Sunday afternoon flyer.

    Thanks for your help,

    Harvey

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    Weather Geek

  2. #2
    mgnostic's Avatar
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    RE: Need help with lightweight twin rudder linkage

    A pull - pull system with Spiderwire fishing line would be very light. Sounds like you are looking for R/C assist so if you do just one rudder there will be a little bit of asymmetrical drag but it should fly like a plane with a small rudder and a big fin. The Twin Lizzie has been on my to do list for a long time. I have a Lulla-Bi fuse framed up and need to finish cutting wing ribs some day.
    Matt Kirk

  3. #3
    H5487's Avatar
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    RE: Need help with lightweight twin rudder linkage

    Hi Matt, thanks for your reply. How would you route the spiderwire?

    Harvey
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  4. #4
    combatpigg's Avatar
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    RE: Need help with lightweight twin rudder linkage

    The bell cranks and control horns can be made with 1/16" plywood. I would press eyelets into the bellcrank pivot holes for durability. You could also make the bellcranks out of thin nylon or aluminum.
    The bellcranks might need to be built up into 2 tiers so that the incoming thread doesn't rub against the out going thread.
    Once you dive into your project and start locating the major pivot points and end points it will become obvious to you what details you need to hurdle to get there.
    To take up slack in the rigging, I run the thread in a continuous loop starting at one side of the rudder horn, through both holes in the bellcrank, then terminate the thread in the opposite side of the rudder horn.
    Take a T pin and wind it up on any part of the loop of thread to take up slack, then secure the pin to the thread so it can't unwind.
    To keep the rudder centered, use a #2 screw and locknut to clamp the thread to the bellcrank and hit it with thin CA.
    WHO GUNNA FEED MAW KEEEIDS..???

  5. #5

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    RE: Need help with lightweight twin rudder linkage

    This is from the airboat section of this forum . I know that this is built far heavier than you would want but the idea is there . .... D.J.
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  6. #6

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    RE: Need help with lightweight twin rudder linkage

    I used a torque rod setuip on my Pee Wee Pal. Worked great!

    Bob Harris
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  7. #7

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    RE: Need help with lightweight twin rudder linkage

    Found this here on RCU: a way to use the elevator hinge wire to actuate twin rudders!
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  8. #8
    H5487's Avatar
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    RE: Need help with lightweight twin rudder linkage

    These are all interesting ideas.

    Thanks!

    Harvey
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  9. #9
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    RE: Need help with lightweight twin rudder linkage

    Hmm. with the Spiderwire one could tie the rudders together and set it up as a closed loop with horns on the outboard side of the rudder. The down side is that your linkage is all hanging out in the breeze. I find myself linking BobHH's setup. Simple and light.
    Matt Kirk


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