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Thread: Wing incidence

  1. #1

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    Wing incidence

    Ok here we go, my head is in a spin and already completed 20 turns. Lol.... I have read the wing incidence on a PA18-150 should be + 1.813 deg on the bottom of the root rib. Also have seen published +1 degree on the root rib. Of course the airframe level in the longitudinal and lateral axis. I have also been told the reading should be taking in line with bolts that attach the wing. Someone throw some more rudder in.

    This is an Experimental airframe, so if the incidence is measuring + 1 degree and should be + 1.8 how much will it effect flight?

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    .8
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    +.8 degrees? And where should you measurement?

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    Just being a dumbass. I don't know what it'll do but Id rather have .8 degrees more than .8 degrees less. Others would say the opposite. I'd expect your takeoffs will be a few feet longer and your cruise speed a few MPH faster.

    The best two guys I know to ask about rigging measurements are AKPA-18 and Cubflier, both who check in once in awhile.
    Last edited by stewartb; 09-21-2020 at 07:13 PM.

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    BC12D-4-85's Avatar
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    Easiest way on a bare frame is to put 2 AN5’s in the wing fittings and use a 29-1/2” straight edge and a digital level, zero the level out on the 2 tubes between the front gear fittings and the rear fitting’s that should be inline with the horizontal reference line that all angles should be measured against, you can also use the firewall as an alternate. The number should be between 4.4*-5.3* with 4.8 equal to the 1.84* you are looking for, the closer to 5.3 the better.

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    PA-22/20-160
    That's one way I have checked and getting around 4.48* using this method.

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    My head is spinning!

  10. #10

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    Quote Originally Posted by Bucrepus View Post
    My head is spinning!
    What’s confusing? You have a fuselage that meets piper’s spec On the low end but could fly a lot nicer if you fix it now.
    Thanks barrow pilot thanked for this post
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  11. #11

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    Here is an article on wing incidence that will raise some discussion.
    https://www.flyingmag.com/pilots-pla...ing-incidence/
    Thanks barrow pilot thanked for this post

  12. #12

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    It is not just the wind incidence you have to think about. Also the tail angles and engine thrust line. A higher wing incidence will give you a better view over the nose but now you have to adjust the tail for proper decalage, also the engine thrust line. Another thing to consider is are you doing big keller flaps and what effect do they have on the cord line of the wing when deployed and how does this effect the stabilizer decalage? Just more to ponder.
    DENNY

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    With a fixed incedence angle, the decalage is variable in respect to incedence, with the trim of horizontal stab. Just thinking out loud. Is trimming the aircraft nose UP and Down causing the decalage to go positive and negative?
    No tricked out plane here just building a widebody with standard wings.

  14. #14
    skywagon8a's Avatar
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    Quote Originally Posted by DENNY View Post
    It is not just the wind incidence you have to think about. Also the tail angles and engine thrust line. A higher wing incidence will give you a better view over the nose but now you have to adjust the tail for proper decalage, also the engine thrust line. Another thing to consider is are you doing big keller flaps and what effect do they have on the cord line of the wing when deployed and how does this effect the stabilizer decalage? Just more to ponder.
    DENNY
    decalage

    N1PA
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    Right, he should have said "longitudinal dihedral".
    What's a go-around?

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    Or angle of the dangle. Because we all understand what he was talking about.

  17. #17
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    You are closer to the design wing incidence than you think. Read the thread posted by tempdoug. It is the one of the more accurate references to wing incidence and associated angles. As for using AC 43-16, be careful there, as you cannot read that document in literal terms. The wing incidence of 1.843 that Gordon Mandel is referring to is not a reference to bottom of the spar caps. It's a reference to the bottom cord of the wing rib. To convert to a spar cap reference you need to subtract .5 degrees. Another quick measurement is to see if there is a 2.5 inch difference between wing attach points in relation to the HR. In a perfect world you can take this from the tube that defines the bottom of the window to see if you are close.

    In the building process an easy way to add incidence is to use Javron's doublers that can add 1/4 to 3/8 inch as I recall.

    I am curious about your wide body fuselage. Is it new airframes or home grown?

    Have fun with your project.

    Jerry
    If it looks smooth...it might be

    If it looks rough...it is!!
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  18. #18

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    Tempdoug,.

    Curious on how to arrived at 1.8 deg aft of the jackscrew tower. I keep coming up with 1 degree 3 minutes. my calculations were based on 9.574" from the hor. ref line to the center line of top longeron directly below the jackscrew (cluster) and the 10.125 from horizontal reference line at the tail post to top logeron.

  19. #19
    cubflier's Avatar
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    Quote Originally Posted by Bucrepus View Post
    Tempdoug,.

    Curious on how to arrived at 1.8 deg aft of the jackscrew tower. I keep coming up with 1 degree 3 minutes. my calculations were based on 9.574" from the hor. ref line to the center line of top longeron directly below the jackscrew (cluster) and the 10.125 from horizontal reference line at the tail post to top logeron.
    The thread is from another member SD2.

    Here is how I come up with his answer.

    Take inverse sine of ((16 - 5.438 )/29.438 ).

    Notice 10.125 does not extend to the HR.

    Click image for larger version. 

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    Jerry
    Last edited by cubflier; 09-25-2020 at 03:16 PM. Reason: fix the smiley face error with sunglasses from 8 next to )
    If it looks smooth...it might be

    If it looks rough...it is!!
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  20. #20

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    Click image for larger version. 

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    Jerry,

    The print on the right is North Land Drawing, print on the left is other Drawing.
    If you look at the difference in the reference line there's an .437" difference.

    Left Drawing

    angle= 1.897 deg

    Right Drawing

    angle= 1.048 deg

    This is also the reason in another thread I couldn't use the factory aft horizontal support bracket and had to use the other.

    Jerry Thanks for inadvertently pointing me to the reference line. Now the million dollar question how much will this affect flight?

    If I use the other aft stabilizer support bracket I have the correct amount of Trim Travel 4 degrees down 2.5 degrees up.

    Oh the unknown
    Ignorant is Bliss!
    Last edited by Bucrepus; 09-25-2020 at 06:32 PM.

  21. #21
    algonquin's Avatar
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    Look at the difference between the -18 -12’s , i can’t remember the difference but it might give you an idea how it will fly.

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