Bearhawk Aircraft Bearhawk Tailwheels LLC Eric Newton's Builder Manuals Bearhawk Plans Bearhawk Store


No announcement yet.

Is it possible to have a rib come out of the wood former flat/straight?

  • Filter
  • Time
  • Show
Clear All
new posts

  • Is it possible to have a rib come out of the wood former flat/straight?

    Hi guys

    ive been practicing making some flap and aileron ribs and they all seem to come out of the jig with a slight bow..that I then fix with a few I doing something wrong I thought these should emerge from the forming process flat...

    is there any method that can make a rib that has no airfoil curves be flat....or do all ribs made in wood formers regardless of the amount of curve in them come out with a bow(just the nature of the process)

    happy Father's Day
    Last edited by way_up_north; 06-17-2018, 12:32 PM.

  • #2
    If you’re bending with a hammer, there are always going to be uneven bending stresses. They should tweak out pretty easily. You could potentially use an air hammer or rivet gun with a flow forming head and get a more even hammer/stretch. But if you can tweak them flat with fluting pliers or similar, then I’d just go with that. Otherwise you’re probably looking at expensive hydroforming processes.
    ​Christopher Owens, EAA #808438
    Project "Expedition"
    Bearhawk 4-Place Scratch Built, Plans #991
    Bearhawk Patrol Scratch Built, Plans #P313
    Germantown, Wisconsin, USA


    • #3
      When you form the flange, you are stuck with too much metal in the flange and you also expand the flange a bit as well. If the ribs were straight on the sides and not curved, you would not have the problem. The tighter the radius you bend around the more distortion you will get. This is why we have fluting pliers. When you flange the lightening holes, you will have to opposite problem.

      Find a way of marking where you want to put your flutes so all the ribs will have the flutes in a straight line along the wing.


      • #4
        The rib taking a curve is normal as bending the flange leaves the outside edge vertical of the fold and on the curve the outer edge is longer than the line along at the bend so it has to curve. The curve is more pronounced on the nose ribs. The joggles take the excess material out so the rib straightens out by shrinking the outer edge with pie tucks.
        As S Lathrop said. Mark all your rivet lines so that you do not joggle on the rivet row. It also makes for consistent ribs. We marked our rivet lines on the hammer form and transferred the lines onto the rib flanges. Check that the flange is square to the work surface once you have the rib flat on the table. It usually requires a few gentle taps to get it perfect. After a few joggles it comes pretty natural as to how deep to set them. We made joggle pliers out of a large set of vice grips and once we had the grips dialed in the process went fairly quick.
        Last edited by Glenn Patterson; 07-11-2018, 12:05 AM.


        • Glenn Patterson
          Glenn Patterson commented
          Editing a comment
          If you have some cupping across the rib that is from forming the flanges. Use a Bob stick and pry up on the hole flanges on both sides of the flanged holes on the long centerline and they will flatten out. That's a tip that I read on the old BH Forum before we started our ribs and it worked good. To get press a rib is efficient and run from there as you have jumped a lot of steps.

      • #5
        I am pressing my nose ribs with a thick rubber block into a wood form block. That folds the outer flanges about 80 % and does the holes all the way
        to 30 degrees. I finish the outer edge with a rubber dead blow hammer. I say finish---- but that doesnt get it all the way either.
        Then it goes through the "cornering tool" that the RV builders use. That brings the edge to about 90 degrees--- but there is some front to back
        curve. Then I fluit the edges......which afterworld---- it is generally flat or nearly flat.

        I THINK---- the cupping is an artifact of the material being allowed to stretch in the zones which are not intended to be stretched.....
        and I think it happens because the sheet is not trapped tight enough (or not at all) in the areas we want to keep flat.

        I have made a video of the hydroforming but I have to figure out how to edit the chunks together.......