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Flap and Aileron Aft Rib different on plans???

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  • Flap and Aileron Aft Rib different on plans???

    I am expecting my order for .025" aluminum sheet this week and was preparing the forms for the various ribs and noticed that the Aft rib on the flaps is different than the aileron on the plans.

    The aft rib on the flaps is almost flat where the aileron has some curve to it... does anyone know if it should be built flat or with the curve of the full size rib provided on SHT 4?

  • #2
    I just checked a factory aileron and flap rib on a very flat plane. No sign of a curve in the aileron rib flange area. All flanges common to the fabric covering lie flat on the plane. Don't have the dwgs close by, I'm curious.
    Patrol #30


    • #3
      Here are a couple pictures from the plans, what got me started on this was that I thought that I would use the same form for each and just shorten the flap to get the aileron... but when I looked at the aileron I noticed that it was much different.

      Aileron Aft Rib.jpg

      Flap Aft Rib.jpg
      Last edited by Derrick; 04-06-2020, 07:09 AM.


      • #4
        I don't have an answer, but I speculate that the aileron rib should follow the contour of the airfoil unless things have changed.

        Your aileron nose rib sparks my curiosity. I wonder when it was changed, why it was changed, and which design is the latest. Suspect yours is latest, but your plans don't have a date on them. Drawing 12 on my plans are dated 10-11-2000 and are Plans #303 purchased may 6 to 7 years ago. The name of the aircraft on my plans is not Bearhawk Patrol, rather Bearhawk (2 Place). The aileron from the Kit is built IAW my drawing.

        Screen Shot 2020-04-06 at 8.21.47 AM.png
        Attached Files
        Brooks Cone
        Southeast Michigan
        Patrol #303, Kit build


        • #5
          Derrick, I would call Bob and ask him if this is intentional. The Patrol and B model Bearhawk have a Ribblett airfoil. It's interesting that in his book, Ribblett says that control surfaces can have a slightly thicker curved upper surface to improve effectiveness. The diagram he shows has the upper surface of the aileron noticeably above the basic airfoil shape, which your plans don't show, although you can certainly see more curvature than on the flap.


          • #6
            Brooks, I assume you can still get an updated set of plans from Bob for a very reasonable fee. I did that awhile back with my 4-place plans.


            • #7
              At the end of the day I don't think it will have a huge difference... it is just at the point where if there is a "right" or "better" way then I want to take that route.


              • #8
                This topic sounds vaguely familiar, but at any rate I'm pretty sure I used the mylar for all the aileron and flap contours. The mylar shows the location of the aileron and flap spar centrelines so I went with that to size up those ribs.
                Scratch building Patrol #275
                Hood River, OR