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Engineering Change Notice for Max Flap Speeds: 4-Place Model B, Companion, and Patrol

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  • #31
    Richard, I think the best course of action may be to contact Bob directly so that you can tell him what you need and have him provide it. If the international logistics are a challenge, I'm happy to help, just let me know. In the USA we don't have the regulatory concerns that you do there.


    • #32
      The language for this update has been revised slightly to clarify that the deflections are based on air loads. I have modified the original post with the updated language and also updated the entries at


      • #33
        I am building a 4-Place with Model A wings. I really enjoyed the recent paper by Russ Erb that discusses his testing of inflight flap deflections vs. on the ground. He did a great job of explaining how cable stretch is a major contributor to the inflight deflection being less than half of the deflection on the ground. He states at the end of the article that Bob Barrows suggested that flap torque tube twist should also be examined. Since the formulas for calculating twist are outside of my current knowledge, I decided to simply measure it. My measurements show with 40 ft-lbs of torque on the flap torque tube results in 10 degrees of twist. I used 40 ft-lbs based on my estimate of 80 lbs of pull at the flap lever ratioed up by 3 to find lbs pull, divided by 2 to get the per flap pull, and then dividing by 3 to get the torque acting on a 4" flap arm. This reinforces what Kestral has observed on his cable-less flap system. Kestral's system also has a cross plane torque tube which add an additional 4 degrees of twist totaling 14 degrees. Very significant!

        Does this make sense or am I way off?


        • #34
          Given that I have 45 degrees on the ground and 30 degrees at stall (less at any higher speed), your numbers look reasonable.