Stall progression

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by pictsidhe, Mar 25, 2019.

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  1. Apr 6, 2019 #61

    Heliano

    Heliano

    Heliano

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    aileron kinematics.jpg

    Differential aileron deflection (the upward deflegtion larger than downward deflection) in light aircraft is the rule to reduce adverse yaw, not the exception. It really reduces (but does not eliminate) adverse yaw. Usually the aileron bellcrank is designed to produce this kinematics. Larger aircraft use roll spoilers in conjunction with ailerons to practically eliminate adverse yaw.
     
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  2. Apr 6, 2019 #62

    radfordc

    radfordc

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    Of course it's true. Airfoils should be designed for the purpose of the planes usage. As a glider flyer, you are concerned with maximum performance and your airfoil should be one that provides best lift over drag....at the expense of gentle stall behavior. For an ultralight, maximum performance is less important and an airfoil that provides relatively gentile handling and stall is needed. Most any flat bottom/curved top/reasonably thick airfoil will do that.

    As for model airplanes even flat plate airfoils work adequately. Here is a video of me flying a 1/3 scale Fokker triplane that uses a flat plate airfoil (Kline-Fogelman type 2). Again, for light wing loadings airfoils are less critical.

     
  3. Apr 6, 2019 #63

    Sockmonkey

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  4. Apr 6, 2019 #64

    pictsidhe

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    Good stuff BJC. I have pondered using something like a 5 digit to facilitate mild aerobatics, but then I was looking at tip stalls as the stall would move outboard, and my good sense took over. Maybe for the next plane...
     
  5. Apr 6, 2019 #65

    BJC

    BJC

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    I have no experience with reverse taper ailerons. My neighbor developed an 8 aileron set-up on a biplane for a well known airshow pilot. As might be expected, the outer four deflect more than the inner four. That airplane has a big rudder that can deflect up to +/- 60 degrees. It will tumble all the way to the ground.


    BJC
     
  6. Apr 6, 2019 #66

    radfordc

    radfordc

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  7. Apr 6, 2019 #67

    Sockmonkey

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    Unless the inner ones also doubled as flaps, reverse tapered ailerons would have let him use one per wing, assuming that they didn't confer any other specific advantage.
     
  8. Apr 7, 2019 #68

    lr27

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    Flat plate airfoils are good for aircraft that are grossly overpowered, very light, and are either made of unobtainium or are small enough to avoid structural issues. KF "airfoils" have no advantage beyond being easy to build.

    It's not always necessary to sacrifice stall behavior to get good L/D. I've flown a couple of gliders that were excellent performers but had relatively soft stalls. For instance, Mark Drela's famous Bubble Dancer.

    For ultralights, if my investigations are any guide, some sections will provide significantly more lift than arbitrarily chosen TLAR airfoils. And not necessarily at the expense of bad stall behavior. Why pick a mediocre airfoil with good stall behavior when you can have a good one?
     
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