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Thread: Therapy Project

  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
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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
    RVBottomly's Avatar
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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?


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  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
    Southern Aero's Avatar
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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
    RVBottomly's Avatar
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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....

  22. #382
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    Year-End Update

    So, more than three months have gone by since my last post. And a little over 3 years have gone by since I started the thread.

    I took some time to re-read the thread. I'm struck by how much help and encouragement I've gotten. I really am thankful for all the support and ideas that have come up. Some of them I had forgotten. I should re-read things more often.

    Not a whole lot has gone on since September. I took the fuselage down from the rafters to test wing attach points, and found out, to my surprise, that they were a little askew. More than a little, like 3/16" off. Rather than jury-rig a fix, I took out the cut-off wheel and started over. Everything now is aligned well. Labrador Cub has me beat by a little, but my wing attach fittings line up so that they are parallel with each other measured at the tail within 1/16". 1/16 over more than 100" seems pretty satisfactory.

    Other than adding a few tabs and starting on fabricating float fittings, little else has happened. I have excuses. My world has readjusted drastically.

    I started the thread talking about how I wanted some therapy from public-defender work stress. From June until October, the stress doubled at least. I had four serious-crime jury trials in 5 weeks--all during the Covid restriction phase. In fact, our county was the first in our state to start having trials. Bigger counties came to see how we were doing it, maintaining social distancing with jury pools of 80-100, etc. It took a lot of creativity.

    The most recent trial did me in. It was a serious sex crime trial involving a young girl. When it was over, I told the prosecutor I was done. He is the elected prosecutor--the boss--and he looked at me and said, "me too. My deputies will handle these from now on."

    The other excuse was that my wife was diagnosed with dementia. It progresses rapidly. I spent the last couple months wrapping up my other cases so we can spend more time fishing. She loves fishing and it is one thing she remembers well.

    Normally I wouldn't go into such details of life's troubles, but I consider a lot of you my friends. My friends here locally know what is going on, I figure you all should too.

    So, I am very much a part-timer these days. My days are still occupied, but with other things. And the project still calls out to me. After these few months of regrouping, I am looking forward to picking up where I left off and pressing on.

    Plus, as I've mentioned elsewhere, I'm an airplane owner. I bought the Commonwealth 185 I talked about last Spring. She was airworthy, but I was suspicious of it a bit. I flew it a few times and was delighted with how she flew, but I didn't like that she had broken stringers from a too-tight fabric job. The owner sold it to me for the value of the C-90, which is in excellent shape. When I finally convinced an IA to do an annual on it, he was suspicious too. But he dug in and looked hard everywhere, fixed the stringers and did a partial recover. She is sound. I hope to have her back in a couple of weeks. I ought now to have time and resources to make it to Johnson Creek this summer, should we all have that chance.

    End of ramble. Thanks to all who have given me encouragement and help. This is a great community, and I look forward to meeting some of you in person in the not-so-distant future.

    Happy New Year!
    Last edited by RVBottomly; 12-31-2020 at 10:39 PM. Reason: typo

  23. #383
    BC12D-4-85's Avatar
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    Best wishes for strength RV and a better New Year.

    Gary
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  24. #384
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    Vic, I had a good friend (now gone west) who also was in the same occupation as you. His therapy was rebuilding airplanes in his garage. He wasn't good at it, but his enthusiasm was boundless. His wife also was in the same situation. Our thoughts and prayers are with you. Good friends are very important during these times.
    N1PA
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  25. #385

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    Got to be nice to finally say "I am done" To stand at a riverside or spend some hours in a boat. Maybe even get a nice meal out of it.
    I stare at my plane, trying to figure out how to get my mind into it while being overwhelmed with other tasks.
    Regards, Charlie
    Super Coupe E-AB build in process
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  26. #386
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    RV you and your wife are in my prayers
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  27. #387
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    RV, take the time to enjoy life, as it is short. Sounds like you are on the right track.
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  28. #388
    Southern Aero's Avatar
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    Vic

    I can relate to what you are up against, been there, a little different, but been there .............. The project will still be there when the time comes
    ......... It doesn't cost any more to go first class! You just can't stay as long.
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  29. #389

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    So this looks like a good place to start with my question: I have a PA-18A that I am doing some work on. Several of the tubes in the door frame and aft cockpit need replaced. The drawings I have are calling to 1025 steel tubes. Is there a specific reason fro this. Has anyone replaced these tubes with 4130? What would the Super Cub community recommend?

    Cheers

  30. #390
    mike mcs repair's Avatar
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    Quote Originally Posted by mstocker1983 View Post
    So this looks like a good place to start with my question: I have a PA-18A that I am doing some work on. Several of the tubes in the door frame and aft cockpit need replaced. The drawings I have are calling to 1025 steel tubes. Is there a specific reason fro this. Has anyone replaced these tubes with 4130? What would the Super Cub community recommend?

    Cheers

    either is fine...
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  31. #391
    RVBottomly's Avatar
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    Thanks everyone for the encouragement. I'm starting to regroup and engaged in a few sub-projects.

    The Wag design for the pedal assembly calls for a torque tube within a torque tube. Because it is side-by-side, you have to make both right and both left pedals work as a unit.

    My Commonwealth Skyranger simply has two sets of rudder torque tubes next to each other. It works fine and I still might go that route in this project.

    But, I decided to try to do it as designed (mainly because I saw pictures of jimboflying's pedals and they looked nice.)

    Layout:

    Click image for larger version. 

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    I didn't take a picture, but after this I nested the tubes in some 1/4" angle iron and clamped them in two axes to keep them straight. I also kept the thick-walled 3/4 tube inside the 7/8 tubes to maintain alignment.

    Initial welding:

    Click image for larger version. 

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    The inner tube has been removed, but there was a story behind that. I knew that things would be tight after welding and the resulting distortion, etc. But this was TIGHT.

    I put the triangle in a large vice, found an 11/16 round stock bar and ended up using 5 pound hammer to drive it out. The inner tube is supposed to rotate. Not yet, obviously.

    So the next idea was to ream it out somehow. I ended up making a barnyard reamer out of thick-walled 3/4 4130. I cut some notches in the end, heated the tip up to cherry red, and quenched it in water.

    I know, pretty sketchy.

    Click image for larger version. 

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    I loaded the tube with cutting oil, and put the "tool" into the assembly until I hit a blockage, tapped the end with a hammer to go another 3/16" or so, and turned the vice grips. When it loosened up, another tap. Continue.

    After about 10 minutes the entire assembly allowed rotation. It's still stiff--I might try some lapping compound or maybe rig up a red-neck cylinder hone, but even just turning the tube with lubrication shows improvement over time.

    Click image for larger version. 

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    In the heat of the moment, I didn't get more pictures or take videos, but I was pleased with how it turned out.

    I'm also working on the stick torque-tube assembly. The problem I'm having though is committing to an approach. After laying out the pedals, I'm starting to think this project ought to be a wide-bodied tandem. I'll have to sleep on it a few nights.
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  32. #392
    Gordon Misch's Avatar
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    Give some thought to material removal - and - how much is left in that outer tube. Another possibility would be to drive a hardened bullet through that outer tube, with heat on the outer tube if necessary.
    Gordon

    N4328M KTDO
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  33. #393
    RVBottomly's Avatar
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    Quote Originally Posted by Gordon Misch View Post
    Give some thought to material removal - and - how much is left in that outer tube. Another possibility would be to drive a hardened bullet through that outer tube, with heat on the outer tube if necessary.
    Right now, the only stuff removed was slag from the weld penetration. The outer tube is 7/8 with .058 wall thickness. I like the bullet idea, but I think I'm so close now that it's just a matter of polishing a little.
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  34. #394
    skywagon8a's Avatar
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    Be certain there is copious lubrication between the tubes on final assembly. They will not be moving in relation to each other a great deal so could over time build rust, restricting smooth motion. Place a grease zerk in the middle or apply a liberal coating of anti-seize or waterproof grease between the tubes. This has been an issue on the stabilizer connecting/pivot tube at the tail post. Small motion = increased susceptibility to rust build up.
    N1PA
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  35. #395

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    I like to use bushings, When I make that type of structure I utilize tubes with enough difference in diameter that I can install Delrin or HDPE bushings for the inner tube to ride in.
    Regards, Charlie
    Super Coupe E-AB build in process
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  36. #396
    RVBottomly's Avatar
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    Quote Originally Posted by skywagon8a View Post
    Be certain there is copious lubrication between the tubes on final assembly. They will not be moving in relation to each other a great deal so could over time build rust, restricting smooth motion. Place a grease zerk in the middle or apply a liberal coating of anti-seize or waterproof grease between the tubes. This has been an issue on the stabilizer connecting/pivot tube at the tail post. Small motion = increased susceptibility to rust build up.
    I agree, Sky. All my years building and working on farm implements makes me want a grease zerk whenever there is steel to steel movement. But looking more into it, I noticed that the Aztec rudder pedal assembly below (found on ebay) is almost identical to what is drawn on my plans. Do these call for lubricant every annual or so?

    Click image for larger version. 

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  37. #397
    RVBottomly's Avatar
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    Quote Originally Posted by CharlieN View Post
    I like to use bushings, When I make that type of structure I utilize tubes with enough difference in diameter that I can install Delrin or HDPE bushings for the inner tube to ride in.
    I knew you'd say that! I really want to use bushings like that here and on the stick torque tube assembly. So far I've kind of been overwhelmed in locating supplies and also design. Would you use a simple bushing that is free to rotate within both tubes, or fixed to one part, so to speak?

  38. #398
    Gordon Misch's Avatar
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    Bushings would be pressed into the outer tube.

    Along the lines of what Sky was saying, you don't want too close a fit between inner and outer tubes. If too close it wouldn't take much to get them sticking to each other.

    No need for great precision. I'll suggest you check out these references re fits. Metal to metal, maybe RC 7 or 8? With bushings, maybe RC 5 or 6?

    https://www.engineersedge.com/mechan...tolerances.htm
    https://www.engineersedge.com/calcul...tolerances.htm
    Gordon

    N4328M KTDO
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  39. #399
    skywagon8a's Avatar
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    Quote Originally Posted by RVBottomly View Post
    Do these call for lubricant every annual or so?
    I would think so, though I wouldn't be surprised that they never get lubed.
    N1PA

  40. #400

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    Quote Originally Posted by RVBottomly View Post
    I knew you'd say that! I really want to use bushings like that here and on the stick torque tube assembly. So far I've kind of been overwhelmed in locating supplies and also design. Would you use a simple bushing that is free to rotate within both tubes, or fixed to one part, so to speak?
    One source to look at is Mcmaster All sorts of wall thicknesses, diameters and material. I like to plan on a 1/16 minimum wall bush so call it about 1/8 between the inner OD and outer ID. You can run thinner. Being these applications the bush is a rather low load, generally snug on the OD. With a steel tube I would prefer the inner tube to be a bit loose simply to allow oil to remain as an anti-corrosive. I am prone to use stainless steel where the loads allow. This allows a more snug fit since the need for corrosion protection is reduced.

    Material choice, Bronze is readily available but with today's engineering plastics the plastic holds up better.

    If you need to add clearance to make something free running, use an appropriate outer tube clamped in the lathe allowing you to cut the ID. Other option is a reamer should you have one or justify the cost.

    Do NOT try to drill these, it might work but probably will not.

    Plastic bushings for high loads should be snug, low loads can be loose.
    Regards, Charlie
    Super Coupe E-AB build in process
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