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Thread: extended leading edge

  1. #1

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    extended leading edge

    Hey all, I'm rebuilding a cub, the wing's I thought were ready for cover, my IA overseeing the project and also a very experienced and great cub builder, suggests I extend aft of the leading edge skins, another 6" or so on the upper surface. My question is: Why would you want to do this? I know Heavy fabric causes scalloping between the ribs. Does this extension reduce the scalloping? Thx

  2. #2
    www.SkupTech.com mike mcs repair's Avatar
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    yes, and it's about 15" you want...

    the scalloping is caused by someone shrinking/installing the fabric wrong...

    you need to tighten end to end FIRST in the bowed area that tends to scalp, NOT front to back! then there will not be much scallop

  3. #3
    www.SkupTech.com mike mcs repair's Avatar
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    also the weight added for a set of 2 wings is about 7 Lbs... with .020" 2024 T3... if anyone cares..

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    It makes for a stiffer wing. Soooooooo depending on how much twist you want in your wing put them on with the wing twisted the amount you want on the plane. You can still adjust but easier if they are set close to what you want.
    DENNY
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  5. #5
    cubpilot2's Avatar
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    Unless you are experimental then you may be out of luck. Can’t get field approval on this anymore even in Alaska. (Unless something has changed).

    This has been discussed quite a bit here. I will try to find it.
    Ed

  6. #6
    www.SkupTech.com mike mcs repair's Avatar
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    Quote Originally Posted by cubpilot2 View Post
    Unless you are experimental then you may be out of luck. Can’t get field approval on this anymore even in Alaska. (Unless something has changed).

    This has been discussed quite a bit here. I will try to find it.
    Sure you can. Use pk screws


    Sent from my iPhone using SuperCub.Org mobile app

  7. #7
    cubpilot2's Avatar
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    Quote Originally Posted by mike mcs repair View Post
    Sure you can. Use pk screws


    Sent from my iPhone using SuperCub.Org mobile app
    So are you getting it field approved or viewing it as minor because of the screws?

    This is the old discussion.

    http://www.supercub.org/forum/showth...light=Scallops
    Ed
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  8. #8

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    Personally I wouldn't recognize a stiffer wing and Jerry Burr debunked the scallops being a lift issue about 15 years ago. I like the extended metal because it protects the ribs from broom damage when sweeping snow. The top caps on my new ribs are a lot tougher than original Piper, though. Probably unnecessary now.

    I wonder what the fabric life difference would be if there was reliable data available. All the lift tugging on the rib lacing through the years must take a toll.
    Last edited by stewartb; 02-12-2019 at 11:12 AM.

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    Untrue, I know of lots of certified cubs with the heavy fabric applied and the extension of the leading edge over the top...


    Quote Originally Posted by cubpilot2 View Post
    Unless you are experimental then you may be out of luck. Can’t get field approval on this anymore even in Alaska. (Unless something has changed).

    This has been discussed quite a bit here. I will try to find it.

  10. #10

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    What is the current FAA attitude? 10 years ago when I asked about extending LE metal I was told there would be no chance of any wing mods being field approved. Any wing mod including extended leading edge metal would need to go through engineering. I haven't heard that anything's changed since. Anyone have any current info? Nobody cares about yesterday's news.

  11. #11
    cubpilot2's Avatar
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    Quote Originally Posted by stewartb View Post
    What is the current FAA attitude? 10 years ago when I asked about extending LE metal I was told there would be no chance of any wing mods being field approved. Any wing mod including extended leading edge metal would need to go through engineering. I haven't heard that anything's changed since. Anyone have any current info? Nobody cares about yesterday's news.
    That was my experience as well. I have one cub with it that was field approved years ago and like it.
    I haven’t tried lately.
    Scalloping for me is no longer an issue as I found that installing the wing fabric with sewn seams chordwise nearly eliminated them. 1/8 inch max.
    Ed
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    skywagon8a's Avatar
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    Quote Originally Posted by mike mcs repair View Post
    yes, and it's about 15" you want...

    the scalloping is caused by someone shrinking/installing the fabric wrong...

    you need to tighten end to end FIRST in the bowed area that tends to scalp, NOT front to back! then there will not be much scallop
    Quote Originally Posted by cubpilot2 View Post
    That was my experience as well. I have one cub with it that was field approved years ago and like it.
    I haven’t tried lately.
    Scalloping for me is no longer an issue as I found that installing the wing fabric with sewn seams chordwise nearly eliminated them. 1/8 inch max.
    Start by shrinking over all the ribs first. Then after it is shrunk spanwise shrink between the ribs. This will lift the fabric and hold it up while you finish. This will minimise scalloping.
    N1PA
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  13. #13
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    Quote Originally Posted by skywagon8a View Post
    Start by shrinking over all the ribs first. Then after it is shrunk spanwise shrink between the ribs. This will lift the fabric and hold it up while you finish. This will minimise scalloping.
    I agree. I will do an envelope, but prefer blanket for the cleaner finished look., It's about how you put it on and how you shrink it.

  14. #14

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    Got any in flight pics that demonstrate the fabric lifting? Are concave scallops while parked directly proportional to convex scallops under a lift load? I could imagine that some concave scalloping may prevent fabric lifting, but I have nothing to back that up. One way to keep the airfoil shape whether parked or flying is to use extended metal.

  15. #15
    BC12D-4-85's Avatar
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    Cubcrafters has several photos of their aircraft taken from above showing scalloped fabric: http://cubcrafters.com/topcub

    Here's a screen grab of another from Kitplanes:
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  16. #16
    www.SkupTech.com mike mcs repair's Avatar
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    With the extended leading edge the fabric is basically stuck/adheared to the metal. So no ballooning at least at first.


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