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Thread: Therapy Project

  1. #281
    RVBottomly's Avatar
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    A little barnyard engineering follows. It may be my concerns about wing twist are a little overblown.

    Basically, through various approaches I come up with calculated loads leading to a maximum of some 1200 pound-inches of torque on the rear spar over a 9 foot long 18 inch chord flap. If that is spread over 4 hinges, then there is 300 pound-inches for each hinge (figuring center of pressure at 1/2 chord).

    So I was wondering what my frail-looking ribs could handle. I decided to put a piece of 3/4 ply in a vise and stick the rear spar opening of a partially completed rib, and then apply force at the front spar opening to see what would break.

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    At 9 pounds 15 ounces, my plywood-in-a vice failed.

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    I reattached the plywood and got up to 10 pounds before the rib started to twist (in a wing, twist is prevented by cross taping).

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    So, one rib with only half of the gussets on it can hold a torque of 310 pound-inches on the spar without failing. (31 inch center X 10 pounds).

    Then there is the fact that at 14" spacing for each rib, 9 feet of spar is supported by 7.7 ribs. 300 pound-inches times 7.7 ribs is 2100 inch-pounds of demonstrated torque support.

    I suppose that is why people put flaps on the 2+2 without giving it much thought--there seems to be quite a bit of reserve just in relying on ribs, not including stiffness of the spar and other reinforcing.

    I still want to add a stiffening compression rib near hinge points, belt and suspenders I suppose.

    Because I'm a hopeless nerd, the other thing I want to do is empirically verify the torque forces of such a flap at various speeds. I'm contemplating a set up in the back of my pickup that would allow me to measure actual forces at various highway speeds and angles.
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  2. #282
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    Quote Originally Posted by RVBottomly View Post
    A little barnyard engineering follows. It may be my concerns about wing twist are a little overblown.

    Basically, through various approaches I come up with calculated loads leading to a maximum of some 1200 pound-inches of torque on the rear spar over a 9 foot long 18 inch chord flap. If that is spread over 4 hinges, then there is 300 pound-inches for each hinge (figuring center of pressure at 1/2 chord).
    Remember that in order for the flap to exert twist loads on the spar it has to have two points of attachment. One at the top and the other at the bottom. The actuator push rod is the one at the top and the hinges (however many there are) are the one at the bottom. The bottom force will be distributed among the hinges. The twist force will be concentrated at the push rod. In order to reduce the spar twist load you will need to add actuators spread out along the spar. My 110" flap has two actuators tied together with a cable. For spar twisting protection, place the actuator(s) adjacent to a compression rib which will transfer the twist loads to the front spar where it converts to a low vertical load reduced by the lever arm length of the compression rib.
    N1PA
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  3. #283

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    I also will be using two actuators on my 120" flaps. My three hinges hang a stupid long distance below the wing and have structure that travels half way to the front spar. These obviously need additional structure to carry the loads such as you are considering the Pitts style Compression rib. Alternately you can get by with a weldment at each hinge point.
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  4. #284
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    Quote Originally Posted by skywagon8a View Post
    Remember that in order for the flap to exert twist loads on the spar it has to have two points of attachment. One at the top and the other at the bottom.
    You are right, Sky. For simplicity I was putting imaginary actuators at each hinge. The actuator loads will be different if fewer.

    I'm starting to see why Javron put in that reinforcing web aft of the spar.

    In any event, I'm contemplating a torque tube to control actuator arms. It seems that would be easy to keep aligned.

  5. #285

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    I am using a torque tube on mine as well. They can be expensive to make light but they do a very good job keeping the action synchronized with the fewest parts.
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  6. #286
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    Quote Originally Posted by RVBottomly View Post
    In any event, I'm contemplating a torque tube to control actuator arms. It seems that would be easy to keep aligned.
    Good idea, use roller or needle bearings at each support block to reduce actuating loads on the entire system.
    The Citabrias use a torque tube mounted in the fuselage with the control arm mounted just outside the fuselage. This then has just one push rod connected to the inboard end of the flap. The flap then is designed to absorb the torsion loads within itself. The Lake LA-4 with it's long flaps is the same.
    N1PA
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  7. #287
    RVBottomly's Avatar
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    Things are getting tight in my little shop

    Having gotten the ribs completed (sanding and finishing, plus cove reinforcement remains), I felt like laying out some spars and marking locations. I see I'm going to need to do some rearranging of things if I want to work efficiently.

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    I don't have any other shelter for the boat right now, but that would be the obvious solution. Other possibility is to hang the fuselage from the ceiling toward the back during the wing phase.

    One thing I'm still looking for is some data on torque tubes, e.g. twisting strength tolerances relative to diameter and tube thickness. For another barnyard experiment I took some scrap 3/4 x .035, stuck one end in a pipe vice, and twisted the other end with a spring-bar torque wrench and a pipe chain fitting. At about 80 lb-ft the end crumpled but there was no twist over 2 feet. Welding actual arms on it would be a better test. I'm wondering if there is some easy-to-find chart that would give recommended dimensions.
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  8. #288

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    How long a torque tube, just across the fuselage driving the inboard of a flap? Or out to the outer or middle flap hinge as well?
    The length is quite important in this case.

  9. #289
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    Quote Originally Posted by CharlieN View Post
    How long a torque tube, just across the fuselage driving the inboard of a flap? Or out to the outer or middle flap hinge as well?
    The length is quite important in this case.
    I'm trying to get educated enough to weigh the options. Assuming in the neighborhood of 12 feet from approx. midpoint of flap on one wing to the other. That's not a fixed idea, but a starting point.

    That's 3.25 pounds approx. of 3/4 4130 at .035. It seems like 1 inch, even with thinner wall, would be more robust. I'm wondering about other materials too.

    I think I'll have a handle on the actual flap actuator loads in a few weeks.

    Vic

  10. #290
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    Quote Originally Posted by RVBottomly View Post
    I think I'll have a handle on the actual flap actuator loads in a few weeks.

    Vic
    Intentional or not, nice pun
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  11. #291
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    Quote Originally Posted by CamTom12 View Post
    Intentional or not, nice pun
    Unintentional at first, but before I hit post I saw it....

  12. #292
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    Lift Strut Attach hurdles

    Before I assembled the wing, I wanted to get some hardware in order to locate it on the spars. I looked at the Lift Strut attachment fittings and decided I ought to just buy them because of the compound curve in the bend.

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    Great plan, except: "This item is no longer available" at Wag Aero.

    So I launched into an experiment at trying to form these pieces with what I had on hand. It's .063 4130 sheet.

    First I tried the old vise bending approach:

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    It looked sort of OK. But I was nervous about the radius of the bend being too tight. I had to free-hand the compound bend, and it looks sort of ragged.

    So I decided to mill a template out of some 1/4 angle I had.

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    I put an approximately .14 radius in the template, and then decided to try using heat to see if I could bend the sides more easily.

    Of course, I could, but I ended up with nice hammer marks on the upturned sides and tool marks on the back where the work slipped a little.

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    So now I have an assortment of tries, and my head is getting sore from the scratching.

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    These are critical parts, and sort of rare because I'm building a wood wing. I was looking on ebay to see if I could find something. There are wood spar J-3 fittings, "used", and looking more dinged up than what I have already.

    I'm wondering if I need to buck up and fabricate a decent set of dies and get a bigger press. Hammer blows on this sort of thing kind of worry me.

  13. #293
    Gordon Misch's Avatar
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    Maybe take 'em to a fab shop that has a press brake with the correct radius dies? I know of one local here that knows aircraft fabrication very well (super-12.com), but no doubt you have options there as well.
    Gordon

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    My SPOT: tinyurl.com/N4328M (case sensitive)
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  14. #294
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    Quote Originally Posted by Gordon Misch View Post
    Maybe take 'em to a fab shop that has a press brake with the correct radius dies? I know of one local here that knows aircraft fabrication very well (super-12.com), but no doubt you have options there as well.
    Thanks for jogging my memory. It caused me to remember that I met a guy who is a pilot for an aeronautical machine shop that subs work for Boeing and others. He told me if I needed something made up, the local shop has 5 different presses.

    That's exactly the solution.
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  15. #295
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    Did you try a stiff backing plate on the back side with thru bolts going through the pattern, piece to be formed, and then the backing plate to form a sandwich ?
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  16. #296
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    Quote Originally Posted by jimboflying View Post
    Did you try a stiff backing plate on the back side with thru bolts going through the pattern, piece to be formed, and then the backing plate to form a sandwich ?
    That sounds interesting. I haven't tried that. Maybe I'll give it a try this long weekend.

  17. #297
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    I feel your pain....I bent and cracked a front end loader mounting plate on my tractor and I'm just about ready to go buy a new one since it's 1/2" steel and there are 6 holes I need to align and get back where they are supposed to be so I can bolt it back in place. I can weld it just fine but each time I do the heat changes placement of the bolt holes...I feel like the old Johnny Cash song about trying to get the transmission to bolt up to the engine.

    Good luck on yours RV!

    Best wishes to the fellow vets on 11/11/2019.
    Somewhere along the way I have lost the ability to act politically correct. If you should find it, please feel free to keep it.

    There are no new ways to crash an airplane no matter how hard you may try!
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  18. #298
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    Quote Originally Posted by jimboflying View Post
    Did you try a stiff backing plate on the back side with thru bolts going through the pattern, piece to be formed, and then the backing plate to form a sandwich ?
    In addition use a dolly against the part to be bent and hit the dolly with the hammer. This will spread out the impact points reducing the possibility of hammer marks. Make a curved dolly of the proper radius for the compound section.
    N1PA
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  19. #299
    Cub junkie's Avatar
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    Forming .063 4130 like this is a challenge. Your tooling has to be able to withstand the forming process.
    Piper made these out of mild steel. Big difference in the effort to make those curves. There is still a lot of wood wing J3 parts still around.
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  20. #300
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    Wag has them
    ......... It doesn't cost any more to go first class! You just can't stay as long.

  21. #301
    Cub junkie's Avatar
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    Those are wing root fittings. He's trying to duplicate strut attach fittings that also hold a compression member.

  22. #302

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    opps

  23. #303
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    Quote Originally Posted by Cub junkie View Post
    Those are wing root fittings. He's trying to duplicate strut attach fittings that also hold a compression member.
    Right. Wag used to have them...I saw them in an old catalog. They quit stocking them, probably because they were hard to make. I ran across some references about cracks showing up in the bend-- -- the radius was just too small for 4130.

    I spent most of the day fabricating a stout pattern from some scrap railroad rail. I ran out of steam drilling bolt holes, plus I had to tend to a flat on my pickup. But I think I'm on course.

    Sent from my SM-J320V using SuperCub.Org mobile app
    Last edited by RVBottomly; 11-11-2019 at 08:26 PM.

  24. #304
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    RV

    I MIGHT have a set that came with an old Wag 2+2 kit project I bought years ago. I'll check............. Might save you a little grief.
    ......... It doesn't cost any more to go first class! You just can't stay as long.

  25. #305
    RVBottomly's Avatar
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    Quote Originally Posted by Southern Aero View Post
    RV

    I MIGHT have a set that came with an old Wag 2+2 kit project I bought years ago. I'll check............. Might save you a little grief.
    That would be cool!

    Vic

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  26. #306
    www.SkupTech.com mike mcs repair's Avatar
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    also a clue when bending short sides like that, is to cut over size, bend, then trim to size.... i use that quite allot.... also for when rolling things like cowl doors.... form, then cut to final size..

  27. #307
    www.SkupTech.com mike mcs repair's Avatar
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    Quote Originally Posted by mike mcs repair View Post
    also a clue when bending short sides like that, is to cut over size, bend, then trim to size.... i use that quite allot.... also for when rolling things like cowl doors.... form, then cut to final size..
    I think i show that in this video... .062 aluminum

  28. #308
    RVBottomly's Avatar
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    Quote Originally Posted by mike mcs repair View Post
    I think i show that in this video... .062 aluminum
    Mike, I watch your videos and realize I have a long way to go in this fabrication game. Very nice.

  29. #309
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    I think I may have located them.............. in a neighbor's hangar...……. We did some "swapping" years ago. Should find in a day or two. All brace wires and compression struts should be with them if interested. They are the WAG version of the J3 wood spar parts. I'm sure they will need bead blasting and priming/painting.
    ......... It doesn't cost any more to go first class! You just can't stay as long.

  30. #310
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    Quote Originally Posted by Southern Aero View Post
    RV

    I think I may have located them.............. in a neighbor's hangar...……. We did some "swapping" years ago. Should find in a day or two. All brace wires and compression struts should be with them if interested. They are the WAG version of the J3 wood spar parts. I'm sure they will need bead blasting and priming/painting.
    Yes, I'd be interested in the whole lot. PM me when you uncover them.

    Thanks!

    Vic

  31. #311
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    Vic

    Found them.......... sent you a PM
    ......... It doesn't cost any more to go first class! You just can't stay as long.
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  32. #312

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    Amazing project! I was hoping to some like that some day. I just hope I have the right equipment for the projects.
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  33. #313
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    Projects like this are good excuses for buying or making equipment that you might not otherwise have or need.

  34. #314
    RVBottomly's Avatar
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    Quote Originally Posted by jimboflying View Post
    Projects like this are good excuses for buying or making equipment that you might not otherwise have or need.
    Exactly! My material budget and tool/equipment budget are running neck to neck.

    Vic

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