Welcome! Becoming a registered user of ShortWingPipers.Org is free and easy! Click the "Register" link found in the upper right hand corner of this screen. It's easy and you can then join the fun posting and learning about Short Wing Pipers!

Thanks Thanks:  0
Likes Likes:  0
Page 1 of 2 12 LastLast
Results 1 to 10 of 13

Thread: Dihedral Dilemma

  1. #1
    Chris Iriarte's Avatar
    Join Date
    Nov 2012
    Location
    Grosse Ile, MI
    Posts
    326
    Post Thanks / Like

    Default Dihedral Dilemma

    Question about dihedral.

    I suspect mine is off ... threads exposed on the lift strut forks are unequal; 1 thread on the right and 11 threads on the left. The string test per Piper SM 20 shows about an inch more than the specified 4-7/8" from the spar hinge fitting, and the right wing can't be lowered anymore w/o the door hitting the wing.

    First, leveling the airplane. When I use the plumb bob method, the fuselage doesn't look level when I step back and look at the plane. Putting a level on the cross member just behind the windshield from spar to spar and using that produces a more "level" looking fuselage. Anyone else encounter that?

    When I use the 30-inch "off level" check it looks like the left wing has 1/4" more dihedral than the right wing. Rough math shows this would probably correct the approx. 1/2" disparity between the strut forks on the two sides.

    The plane flies straight and level now, trues consistently at 113 mph, but it seems to me the dihedral could be corrected. Any advice from you hard-core riggers out there?

    Chris

  2. #2
    Jim's Avatar
    Join Date
    Nov 2007
    Location
    Fennville, MI
    Posts
    842
    Post Thanks / Like

    Default Re: Dihedral Dilemma

    Hi,

    ......when I use the plumb bob method, the fuselage doesn't look level....

    My upper window channel has several holes from past screws around where the proper hole is located. Are you certain you've found and used the right one to plumb from?

  3. #3
    mmoyle's Avatar
    Join Date
    Mar 2013
    Location
    Platinum Alaska
    Posts
    2,046
    Post Thanks / Like

    Default Re: Dihedral Dilemma

    Drawing 12510 has the centerline drawing fore to aft. 28" below the front wing spar mount bolt center line. Aft it's one inch above the centerline intersection of the lower longeron and tail post. Need to verify that by visiting the drawing again. I'll have to use a laser level for the first rigging. Will shoot a rotating laser through the airplane at the doors.... Could do it through the door and window....if no left door. Measure up from the laser line to the wing spar bolts and down to the tail or laser on the tail dimension mark...


    Sent from my iPad using Tapatalk

  4. #4
    Administrator Steve Pierce's Avatar
    Join Date
    Nov 2007
    Location
    Graham, Texas, United States
    Posts
    12,780
    Post Thanks / Like
    Blog Entries
    1

    Default Re: Dihedral Dilemma

    ve run into similar situations. Fuselage was usually previously repaired and not done so dimesionally correct. All you can do is get it as close as possible. Helped a friend rig his Super Cub that was similar to yours. We had to adjust one side all the way in and then adjust the other side to match. My experience is they don't feel quite as nice with more dyhedral but no change in stall and slow flight. Now you know what you have to do at recover.

  5. #5
    Chris Iriarte's Avatar
    Join Date
    Nov 2012
    Location
    Grosse Ile, MI
    Posts
    326
    Post Thanks / Like

    Default Re: Dihedral Dilemma

    Thanks everyone. I'm pretty sure I'm using the correct door frame hole but I know the plane's been bent in the past. Based on what you say Steve, I think it would be worth the effort to lessen the dihedral.

    Chris

  6. #6
    Administrator Steve Pierce's Avatar
    Join Date
    Nov 2007
    Location
    Graham, Texas, United States
    Posts
    12,780
    Post Thanks / Like
    Blog Entries
    1

    Default Re: Dihedral Dilemma

    I had to bottom out the strut on one side and then match the dyhedral on the other. Fuselage repair is in the works in a year or two.

  7. #7

    Join Date
    Jun 2010
    Location
    Hutchinson, MN
    Posts
    732
    Post Thanks / Like

    Default Re: Dihedral Dilemma

    Like Steve said it is likely the fuselage is tweaked from a past event. I had a similar issue with my Pacer when we went through the rigging. From a functional perspective we finally ended up leveling the plane across the forward wing attach fittings and then progressing from there. When all done it looked much better and were able to get the dihedral correct. Not sure were the issue really was.

  8. #8
    Chris Iriarte's Avatar
    Join Date
    Nov 2012
    Location
    Grosse Ile, MI
    Posts
    326
    Post Thanks / Like

    Default Re: Dihedral Dilemma

    I started this thread 5 years ago, but I'm finally tackling this issue once and for all.

    Steve, for a (tri)pacer, have you found there is a certain number of threads per degree adjustment on the struts? I need to take at least 1 degree out of the left wing.

    Chris

  9. #9

    Join Date
    Mar 2017
    Location
    Frederick MD
    Posts
    857
    Post Thanks / Like

    Default Re: Dihedral Dilemma

    Had a J3 a couple years back that has the fuselage out of square. When we went to adjust dihedral, one side had the strut fittings out as far as I was comfortable and the other all the way in. Before you cover a fuselage itís always a good idea to trammel the thing for square. That J3 was more like a parallelogram then a rectangle when we checked from strut fittings to wing attach fittings!


    Sent from my iPad using Tapatalk

  10. #10
    Chris Iriarte's Avatar
    Join Date
    Nov 2012
    Location
    Grosse Ile, MI
    Posts
    326
    Post Thanks / Like

    Default Re: Dihedral Dilemma

    I did a so-so leveling a few years back and convinced myself the fuselage was bent since it flew hands off and when you stepped back with it "leveled," it still looked off. This time, I really paid attention to the leveling process, cross-checked that the floor was level, firewall was plumb, etc. and the left wing is 1 degree higher than the right. I think what was throwing me is the line formed by the top of the windshield is not level so when you step back, it throws off the picture. But, everything else lines up, the the struts aren't equal, so here we go!! I'm a one-person show so I'm hoping I can get away with "disconnect the wing end, full rotation, reconnect."

    I've done wash out corrections but this is the first time moving the whole wing. I'm guessing I'll have to take the rear strut completely off, adjust the dihedral, then reinstall the rear strut and set the wash out.

    Chris
    Last edited by Chris Iriarte; 06-29-2020 at 06:39 PM.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •