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Wing Chord

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  • Wing Chord

    I just wanted to ask a question about the wing chord of the Patrol. My problem is that I looked up the Riblett 30-413.5 information then started to measure drawing #4 , the full scale wing drawing, and noticed that the dimensions I calculate for a 60", 65" and 66" chord don't match up to the drawing. I made a copy of drawing #4 by hand then glued it to a mdf board to make the master forum block. It has been a while since I did any math like this, the last time I did it was in A and P school 8 years ago but being a machinist I wanted to make sure my copy was accurate. The original drawing lines up exactly on the copy.

    Dose anyone know if the drawing center lines are the same as the airfoil chord and what length of chord the Patrol wing is?

  • #2
    The way that the Bearhawk and Patrol wings are constructed, the angle of incidence is accounted for in the attachment plates on the root end of the spars. So no worries about alignment. The chord should be somewhere near 65-66". The wing plan with a scale, or the full size rib sheet Mylar and a ruler/tape will tell the story.

    Im not sure what you're asking about related to center lines, though. Do you mean the camber arc?
    Last edited by Chris In Milwaukee; 03-30-2017, 08:12 AM.
    ​Christopher Owens, EAA #808438
    Project "Expedition"
    Bearhawk 4-Place Scratch Built, Plans #991
    Bearhawk Patrol Scratch Built, Plans #P313
    Germantown, Wisconsin, USA


    • #3
      You can always get another mylar original from Bob.
      You mean the dash CL on the mylar drawing? Yup, chord. I can't get my CAD to open but I recall it's very close to 65". Are you saying the coordinates of 30-413.5 don't match up with your measurements of the drawing? How do they compare?
      Scratch building Patrol #275
      Hood River, OR


      • #4
        That is right Chewie. I don't have very many numbers right now but I plan on making an excel sheet to calculate the numbers then I am going to draw it out on a blank sheet and compare the two. One example of the measurements I have plotted out is at 33" from the nose the top of the wing should be about 5.414" for a 60" chord and somewhere around 6.6" for a 65" chord however I measure the drawing at about 6.1".


        • #5
          Well, after working on a jig to build wing ribs for an Aeronca L3 I finally put pencil to paper and calculated all the station numbers and plotted them out on a piece of paper for the Patrol. I then compared them to mylar drawing I got with my plans. There is a difference between the two, on the mylar drawing, the top surface of the wing is closer to the chord line and the bottom surface is further from it.
          I don’t think my mylar drawing is in error because I also bought the plans for the 4 place Bearhawk Model B. It uses the same airfoil as the Patrol. The mylar drawing that came with it matches the one for the Patrol.
          Also on the Bearhawk website where they discuss the difference between the Patrol and Super Cub they say the airfoil is
          An efficient, modern Riblett GA30-4135 airfoil developed by Bob Barrows with assistance from airfoil designer Harry Riblett
          So when I cut out my templates I will cut along the line of the mylar drawing.


          • #6
            How much of a difference are you seeing?


            • #7
              I am seeing about of 1 inch on some points of my drawing for the lower surface and 3/4” on the upper. If the pictures get uploaded they are of a copy of the mylar drawing I made and glued to a MDF board.


              • #8
                I'm glad I was sent the link to this topic. I've been studying the same thing and this answers my question. The drawing on the Mylar is actually a slightly modified version of the 30-413.5. I suspect Bob altered it to take the slight "cusp" out of the airfoil and slightly reduce drag. I have plotted the 30-413.5 (with cusp) and the 30A-413.5 (without "cusp") and the 30-413.5 is the closest of the two with the "cusp" removed and a slight camber in its place. I will stick to the Mylar drawing.