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  1. #361
    RVBottomly's Avatar
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    More wing work. Marked out and cut out wing attach fittings

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    Stacked for match drilling

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    Add doublers. Needed to locate them using wood scraps

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    Prepped for edge weld

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    Next was to weld nuts into the wing root compression tube
    I was skeptical.

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    But it worked.

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    The welding made the strut 1/16 too long, but that's what lathes are for. I faced off the ends to make square and to get to the right final dimension. No pictures, though....


    Installed the compression strut to measure the diagonal.

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    I didn't take pictures of how I fit the diagonal, but it was simply a matter of flattening the tube at both ends, bolting one end in place, and then check for square. It was very close because the next bay was square. Adjusted approx 1/16 and vice gripped the other end, made a mark, and drilled the diagonal. Once it was bolted in the bay was right on with the trammels.

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    But now I have to sister in an upright for the rib because of interference.

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  2. #362
    Cub junkie's Avatar
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    If you haven't already give rota-broach's a look. They make round holes instead of five sided holes like twist drills do, especially when stack drilling parts.
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  3. #363
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    I've been lazy posting things, but still working. I ended up doing more wing attach fittings because one of the ones I built before was just slightly too wide for the spar.

    Layout again

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    I don't think I mentioned it before, but I've found cutting .090 4130 works with a cheap jigsaw. For me it's a lot easier than a cut-off wheel. Of course, a bandsaw would be best. I need more room.

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    Match drilled. I didn't use a rotary broach, which looks cool, but I did drill slightly undersized and used a reamer. My mill drill is really handy for these kinds of things.

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    Pretty bad photo, but the mill drill also was useful for trimming things up.

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    Set up the two pieces for tack welding. I milled a scrap steel bar to match the spar thickness, which made a nice jig.

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    Next I girded my loins and drilled the spar holes. Not pictured were square and level I used to make the hand drill go perpendicular to the spar. At first I was going to make a nice jig, but it got complicated...or I ran out of time...or I lost interest. Anyway, I decided to eyeball it using the square and level. The holes went through perfectly, so on I went.

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    Then came trial and error fitting a butt rib

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    Primed things

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    Then put it back together

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    Cut out some nose ribs while paint or epoxy was setting.

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    And, since this is an experimental airplane, I decided to experiment.

    Leftover polystyrene epoxied together

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    Hotwire rig from an old drag wire. I ran 50 amps through it from an AC welder, which seemed to get it hot enough to cut the foam.

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    One thing I learned is that when it gets hot the wire goes loose. So I tightened it some more and was real gentle making cuts. The other thing I learned is that when the wire reached the epoxy joint, things slowed down a lot. Forcing it makes a mess.

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    The point of all this was to make quickly flap prototypes for fitting the flap coves, hinges, and actuator points. It sort of worked, but I'm still mulling over the next steps.
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  4. #364
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    Wow, June is gone and I have little to show for it. It's been kind of rough for the project because my day-job has been opening up. I've been feeling the flood from the backlog.

    I sanded and fine-tuned the flap coves and pinned down where the hinges should go. Then I decided to make hinges.

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    I'm planning to use some 1mm birch ply to enclose the flap coves. A layer of light fiberglass ought to stiffen it up. But first I want to locate the hinges so I know where to put openings through the plywood.

    Other than that, I purchased a new toy (tool). I have an old General vernier caliper, but it reads in 128ths of an inch. My cheapo digital ones are not pleasing to use.

    But this one is:
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    Took me a little while to get used to it, but I get consistent readings +/- 2 thousandths now.
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  5. #365
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    Quick test on flap hanger

    I decided to see how the flap hanger works on a spar. This isn't a perfect test, but it points me in the right direction.

    I bolted one hanger to a 1X4 and put some stress on it. The "spar" is supported 8 inches from the hinge point, which corresponds to the distance from a rib the hanger could be located. Of course, in real life it would be supported by both ends.

    I did some rough lift equation calculations and estimated 27 pounds per hinge at 60 mph. Of course, that would be split with pushrod forces, too, so this is very rudimentary. I pulled it a little past 29 pounds.

    The hanger is very stout. Probably too much so. The spar twist causes me some concern. The real spar is 4.5 inches wide instead of 3.5 inches.

    I think I'll mock up a real test with proper spar size when I get a chance, with ribs on both sides of the hinge. I'm probably over-thinking this, but I want to avoid spar twist with flap deployment.


  6. #366
    Southern Aero's Avatar
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    RV

    Another thing to consider is the "false spar" properly attached to the hanger will help support the hanger and spreads this load thru the ribs t the spar. Its a valid concern as this type of wing structure usually doesn't have flaps.
    Last edited by Southern Aero; 09-21-2020 at 02:45 PM.
    ......... It doesn't cost any more to go first class! You just can't stay as long.
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  7. #367

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    As to your math calculations, I do not see the 1.5 safety factor applied to your loadings?
    For some reason, to me 27# per/ seems very low. I would think normal flight loads when retracted are higher than that for the retracted flap surface area. Mine sure are.
    Regards, Charlie
    Super Coupe E-AB build in process

  8. #368
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    Quote Originally Posted by CharlieN View Post
    As to your math calculations, I do not see the 1.5 safety factor applied to your loadings?
    For some reason, to me 27# per/ seems very low. I would think normal flight loads when retracted are higher than that for the retracted flap surface area. Mine sure are.
    I wasn't even getting to the safety factor yet. You are right, 27 pounds is way low. Looking at it simply from percent of the wing while retracted (3 hinges) it would be 40-45 pounds approximately.

    Back to a closer look at the numbers....

  9. #369
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    Man progress has been slow! I'm doing everything I can to shed some day-job work, but it's getting worse.

    But I'm still obsessed pinning down what happens on a wood spar with bigger flaps. I changed my flap hangers a little.

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    Then I rigged up a little better test stand. The scale in this picture started out at around 29" horizontal moment arm from the spar. As I lifted, the scale was 38" from the spar. So at 30 pounds I was putting 1140 pound-inches torque on the spar. The video shows the ribs starting to distort, but I didn't notice that while staring at the scale. It also is interesting seeing the spar twisting.



    For some reason I didn't reset the camera, but I got re-positioned and was able to get the scale up to 39 pounds. At that point the scale was 40 inches from the spar, so torque was 1560 lb-inches and the table the assembly was on started to lift from the floor.

    I don't know what I was thinking, but I decided to lift up on the bar again until the table started to lift, so I could get a second measurement of the horizontal spacing where the scale attached....SNAP!

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    So I got a pretty cool shot of the failure mode of unsupported ribs.

    And also some useful information. The approximate center of lift of the flaps I have designed is 13.5 inches from the rear spar. That means that 115.5 pounds of lift would be close to the strain I was applying just before failure. I'm still trying to figure out how that works with three hinges and one or two actuators, but I'm thinking that some reinforcement would be a good idea.

    Of course, in real life the ribs would be restrained, but I'm thinking more support against spar twisting is needed. This all is time-consuming, but interesting, nevertheless.

  10. #370
    BC12D-4-85's Avatar
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    Are inter-spar torque brackets at the hanger stations not an option? Metal (typical) or wood. Edit: Like Bellanca?

    Gary
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  11. #371
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    Quote Originally Posted by BC12D-4-85 View Post
    Are inter-spar torque brackets at the hanger stations not an option? Metal (typical) or wood. Edit: Like Bellanca?

    Gary
    Everything's an option! I'll have to look at the Bellanca wing.

  12. #372
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    Aaaaa ok. Simple tubes (round or square aluminum) with end plates that fit between the spars and bolt through them to the hanger brackets. Carry torque loads created by the flap and aileron brackets on the outside of the spar at that station to the front spar. Reduces or stops spar twisting and loads on the ribs. Trammel wire ends typically attach to them. Could be made of wood square stock with glued ends as well.

    Gary
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  13. #373
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    Well done Vic, that is just what a manufacturer would do to verify his design. As Gary mentioned, it is necessary to provide something to tie the two spars together at this location in order to prevent the twisting. By locking your rear spar to a long arm which is anchored to the front spar the twisting loads on the rear spar are removed. This is called a compression rib. Here are some examples.



    This last one is a compression rib which is not designed to prevent twisting. Only as a spar spacer and an anchor location for the drag and anti-drag wires.



    Your ribs which failed are only designed to hold the fabric in it's proper shape. They do not provide any structural strength to the wing. Well a little, but that is not their purpose. All of the loads which are applied to the wing should be considered without these ribs installed. As you have found, they are very flimsy.
    N1PA
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  14. #374
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    Those are good ideas. One of my hangers is in the fuel tank bay., though.

    Maybe move it closer to the wing root?


    Sent from my iPhone using SuperCub.Org

  15. #375
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    How long are your flaps? Can you place one hangar at each end of the fuel bay? That should work out nicely. The compression ribs could double as the ends of the tank bay. Then equally space the hangars over the total flap span. How many hangars are you using? Perhaps you could change the hangar count?
    N1PA

  16. #376
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    Sky, I've settled on 80 inches long, but with a longer chord. I had been going with three hangers, but 4 might do what you suggest. I'll look over things this evening. Good thoughts.
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  17. #377
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    Vic

    I used this method on the outboard aileron hinge, similar to sky's black and white pic above


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    ......... It doesn't cost any more to go first class! You just can't stay as long.
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  18. #378
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    I'd still have a look at what Bellanca did to their wood spar wings, especially the aerobatic focused models. There was always some moveable brackets in the couple I owned if enough force was applied by hand. I could not get the wing tip to visibly twist in flight with full aileron application. Pushing up on a deflected flap would cause some minor movement. Eventually they had problems with loosening nails so maybe there was movement in flight. Better to flex a little than break however.

    Gary
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  19. #379
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    Quote Originally Posted by Southern Aero View Post
    Vic

    I used this method on the outboard aileron hinge, similar to sky's black and white pic above


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    That looks good, but now it has me thinking some more...LOL. The diagonal looks adjustable?

    I'm moving the ailerons out some to fit the flaps. I pretty much decided to keep them as designed, but I had a nagging thought that I'd have to do something like that, too.

    As designed, the ailerons are pretty much stock cub ailerons, approx 105" long, with cable pulls. Three hangers separated by 33 and 35 inches. If I move ailerons out 17 inches, it changes the load centering. Right now the outboard hanger aligns with a rib--no compression strut nearby. The other two are adjacent to compression struts.

    For a moment I thought of trying to imitate the PA14 or PA12 ailerons and use push-pull as actuators, and then I got nervous about getting too carried away.

  20. #380
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    The small rod is just a drag brace after the last compression strut...... no tip bow. I wish you had gone with the metal spars, could just copy Pipers methods with only one bolt in the spar for the hinges and stabilized by the false spar........... How about maybe sheeting the aft section of the ribs with a good bond into the spar and use the false spar method to stabilized them like the metal spar? The loads would be the same as a metal wing just have to get the load from a false spar thru a rib strong enuff to take it. Piper's original ribs weren't exactly beefy but were strong enuff. I try to stay away from wood but there has to be some good "wood" guys on here.
    ......... It doesn't cost any more to go first class! You just can't stay as long.
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  21. #381
    RVBottomly's Avatar
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    Wayne, I'm laughing because I agree with you. More than once I've been visiting the various wing kit websites!

    I have been investigating making a "box" with plywood instead of sheet aluminum. Around and around I go.

    Steady....

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