Balestron angle of attack control

Discussion in 'Sailboats' started by misanthropicexplore, Apr 16, 2020.

  1. misanthropicexplore
    Joined: Apr 2018
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    Location: Upper middle Missouri River

    misanthropicexplore Junior Member

    In some balestron rigs, the jib is mounted to the boom, like this:

    In others, the jib is mounted to a yard with a pivot point at about 30% back from the jib luff, like this:

    https://rcsails.com/cart/images/A-and-B-rig.jpg

    On that second type, when sailing in the points of sail ranging from beam reach to close hauled, does the sailor need to rotate the mast against aerodynamic force to a best mainsail angle of attack (AoA) for each jib AoA, or does the overall of the jib/mainsail assembly AoA automatically adjust/balance itself to the highest lift AoA in response to aerodynamic force? ie, does the whole thing weather vane to the highest lift AoA in response to whatever the jib's AoA is?
     
  2. gggGuest
    Joined: Feb 2005
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    gggGuest ...

    I can't think of any reason why a rig would settle at an optimum angle of attack. Rather the opposite.
     
  3. misanthropicexplore
    Joined: Apr 2018
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    Location: Upper middle Missouri River

    misanthropicexplore Junior Member

    To me, it seems like it would, because the lift forces on jib and mainsail would work on the pivot of the mainmast, something like the way weight-shift steered hang gliders go to a close to optimal A0A when the weight is centered below the cg. I was thinking something like this sketch, with the mainmast offset on a pivoted arm.
     

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    Last edited: Apr 19, 2020
  4. messabout
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    messabout Senior Member

    I can think of no reason to have the mast mounted on a pivoting arm. I can think of several reasons not to use a pivot arm.
    The sketch shows the boom extending forward of the mast to provide a place to tack the jib. I suspect that there are some delicate adjustments to make for differing wind conditions. The tension on the jib stay will have some influence on the tension on the main leech.

    Normal sailing will need the jib to present various slot openings. Usually narrower when going to windward and more open when reaching and perhaps bat winged when on a dead run. RC Model sailboats often have the jib mounted to a deck secured club. Luff and leech tension is adjusted as in your sketch. The club is held down with a line attached somewhere along the length of the boom. That adjustable distance allows the tuning of the jib such that luff and leech tension is best distributed. In any case the jib sheet is best separate from the main sheet if delicate trim is to achieved.

    I have experimented with RC boats with a rig almost exactly like your sketch. The rig works best without a jib. There are some reasons for using a forward boom as in your sketch. When the main boom is close to the deck there is no place for a conventional vang. The tension on what would be a jib stay will act as a vang. Problem is that unless the forward part of the boom is equal in length to the main boom there will be forward mast bend problems because of the difference in boom lengths and the resulting lever ratios. This presumes that the boom is free to pivot up or down by having it secured to the mast by a pivot pin.

    All that said, there are a few full sized boats that have used such an experimental rig. The design principal has not earned much enthusiasm.
     
  5. misanthropicexplore
    Joined: Apr 2018
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    Location: Upper middle Missouri River

    misanthropicexplore Junior Member

    The hope I had for the pivoted arm was two-fold:

    (1.)Not shown in the picture, I was thinking about putting a buoyant counter weight on the opposite end of the arm. In this way, the counterweight would always be opposite the force, regardless of wind direction, swinging over the boat when the wind is from behind.

    (2.) I hoped that combination of the pivots would lead to some sort of ideal balance in which both the arm's pivot and the mast worked together to balance forces. The Wright Brothers used a similarly sort of "double lever" to measure lift and drag. Lift tensions the arm, drag rotates it back, so the angle it assumed was the ideal angle of attack for a given lift/drag ratio. Perhaps to do that, I need something more like an Ackerman linkage, and less like a simple pivot. It is very easy to make all this vastly too complicated to be worth the bother, of course and that idea might be of that nature.

    My idea here is a about a 1 "man power" sail for a solo plus sized canoe. Being that a person's all day paddling pace is less than 100W, it seems like a 15-25 square foot sail is more than adequate for sneaking into the wind at 2-3 mph. Hence, I've been planning on using RG 65 rigs scaled up. The main pivot is mounted to a bow mounted foil which works like a bow mounted rudder.

    The counterweight would cancel out the rolling moments on the x and z axis, with the foil canceling out the left/right sliding on the Y axis. My hope is resolving all the sail related forces in the rig and foil, so that the canoe shape can still be maximized for paddling. Here's another sketch.

    None of that, however, apparently eliminates the careful management of the relationship of the jib angle, to the overall angle of attack of the whole system.
     

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    Last edited: Apr 19, 2020

  6. gggGuest
    Joined: Feb 2005
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    gggGuest ...

    My feeling is that you are at some risk of over complication.
    The historically popular rig for a sailing canoe, by the way, was two masts, each with a single sail, be it lug sail, bermudan or whatever, with one mast close to the bow and the other well aft behind the sailor(s). The advantage of this, of course, was that the rigs could be low to the deck without interfering with the sailor.
     
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