Pat's build thread

Discussion in 'Marquart Charger' started by pbrannan, May 1, 2018.

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  1. May 1, 2018 #1

    pbrannan

    pbrannan

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    Ok, I think I need a build thread for my project as there will be multiple questions related to my build and I don't want to pollute the forum with 75 different topics.

    Here's the first question: Can anyone tell me for certain what type of tailwheel this is? I believe it is an older Maule but no picture matches exactly. The groove for the leaf spring is 1.5 inches. There may have been a center detent at some point, but I think it's pretty well worn down. The bearings seem fine. I would like to know so that I can investigate the possibility of parts.

    There should be a google photos link and an attachment

    https://photos.app.goo.gl/NCzZYU83QTaRgL14A
    [​IMG]

    Screen Shot 2018-05-01 at 1.05.18 PM.png
     
    Last edited: May 1, 2018
  2. May 1, 2018 #2

    gmann750

    gmann750

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    Looks like a API Tailwheel single fork 6” wheel
     
  3. May 1, 2018 #3

    Knight Twister

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    Yup. API and that fork will fit their flat spring mount or their round spring mount.
     
  4. May 4, 2018 #4

    pbrannan

    pbrannan

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    OK. As I posted when I joined the biplane forum, my Marquart is a bit of a repair project because it was in storage so long.

    I discovered a few weeks ago that the paint on the wing fittings was terrible and had to be redone. I've taken care of the left wings and am working on the right wings now.

    In the picture attached, you can see that the nose stringers, which are installed on the right upper, interfere with the top bolt on the forward cabane fitting.

    I know that bolts are supposed to be forward to backward, but would a DAR really go nuts if the bolt was inserted from back to front? I can't see how it would be a safety issue in this case.

    Screen Shot 2018-05-04 at 11.21.17 AM.png
     
  5. May 4, 2018 #5

    Cameron

    Cameron

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    I doubt the DAR will care either way.
     
  6. May 4, 2018 #6

    IanJ

    IanJ

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    Doesn't seem like it should matter. Either way, the bolt and nut are enclosed and can't be inspected in the normal course of events. If there were an inspection ring there, it would be better to have the nut-side exposed so you could see if it was backing off, but even that doesn't seem like a strong consideration, since it should be impossible for the nut to back off if it's secured per plans.

    I'm not sure you'd want to follow my method since your wings are already built up, but I'm assembling my wings without stringers on the leading edge. Since I'm going to build up birch ply leading edges, the stringers are redundant -- they're there to support the ribs side-to-side, and to support the very thin .016" aluminum that's specified for the leading edge material. Because I can glue the rib noses to the ply LE, that covers the side-to-side support of the stringers, and the plywood is strong enough between ribs to not need further bracing.
     
  7. May 5, 2018 #7

    pbrannan

    pbrannan

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    I'm just going to run the bolt in the other way. This particular bolt is one of the long AN4 bolts that holds the plate on. The nut is a typical fiber lock nut. You have to hammer (lightly) the bolt through the hole. Risk of coming loose seems to be zero to me. Either that or cut the stringer.

    One of my local friends here told me Wicks doesn't even sell .016 any longer so it will probably be .020 for me on the leading edge.
     
  8. May 6, 2018 #8

    Alaskamech

    Alaskamech

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    Can you post pics of the project plz. i always enjoy seeing what folks are working on and especially chargers. thx Terry
     
  9. May 8, 2018 #9

    pbrannan

    pbrannan

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    Here are some pics of the project:

    https://photos.app.goo.gl/VBq3UXtasYNJvNpg1

    I have also been taking time lapse of everything on my GoPro. Those are not all that detailed, and are large so I did not post.

    As I explained a while ago, I bought the project partially finished with no build logs. I did this after consulting EAA and local DAR and careful analysis of the FAA task list. My conclusion was that I could conclusively document 51% of the tasks being done.

    The project came with several broken ribs, all but one of which I have fixed. The last one is in progress now. Turns out that fixing ribs is not as terrible as I thought.

    The thing I really hate about the project is that the rear seat was moved back 3" and I am not happy with how it was done. My desire is to change back to plan, but I have not mapped out, weld-by-weld, exactly what I will do to repair yet.

    What I like about the project is that the wood work, drilling measuring, etc., seems to be first rate.
     
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  10. May 12, 2018 #10

    pbrannan

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    Well, all the hardware is painted and the wings are going back together soon. I believe the next step is to fit the wings and drill the lower spar butts.

    To do this I will need to make a wing drilling jig. There's an EAA video on the topic that seems fairly simple and I plan to make something like the example and test on scrap wood.

    If anybody has any better ideas or suggestions to make this less error prone, feel free to let me know. I need to get this right the first time.
     
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  11. Jun 12, 2018 #11

    pbrannan

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    So I'm back from vacation and working on the Charger. As some of you may remember, my frame had the seat moved back 3 inches. I posted a separate thread about this. After much thought, modeling, computation and general hand wringing I decided to cut out the mods and return to plan, and that is what I've done over the last few days. All of the old stuff is cut out, and some of the new tube is notched and ready for welding.

    I did run into a problem with the seat support bracket, -458, on sheet 14 . As it turns out, 3/4" square .058 tube is no longer available. Instead you can get .065. The unfortunate thing about that is that the seat frames are 5/8" round tube, which fits nicely inside .058 square tube, but does not fit inside of .065 inch square tube. So I bored out a couple of .065" tubes and made the brackets.

    It seems like Marquart must have had a large stock of every possible size tube ever made.
     
  12. Jun 12, 2018 #12

    IanJ

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    I've had this same impression.
     
  13. Jun 12, 2018 #13

    pbrannan

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    Ok. I'm sure this is going to make me look like an idiot, but here goes. Attached is an excerpt of the Charger plans. It's the simplest thing in the world, a harness attachment. Basically, it's a loop bent out of a 3/4" strip of 090. 090 isn't exactly wet spaghetti.

    Getting the strip cut is not the problem. Getting a decent bend is. I have a vice, torch, bench, and assorted hand tools. I would be happy to buy something like an arbor press, but would prefer not to buy a massive chunk of equipment for the few parts I have left to make. Seems like it should be dead simple. detail-n.png
     
  14. Jun 12, 2018 #14

    IanJ

    IanJ

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    I think the way I'd tackle this one (the way I most likely will tackle this one, when I get to it) is with a torch, vise and a hammer. Do the "outward" bends (closest to the ends) first, then form the strap around a solid bar of the appropriate size, using heat and hammer as necessary. I'd probably use propane to start with, and switch to MAPP or OA if that clearly wasn't enough heat. Probably the "right" way to approach it would be to make a U-cross-section die that's the OD of the strap, and use a bar to cold-press the strap into the die, though you'd still have to form the outward bends before pressing it.
     
  15. Jun 13, 2018 at 12:19 AM #15

    cwilliamrose

    cwilliamrose

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    That's one beefy part. It is very similar to the Pitts seat belt attach clamps. Those are made from .063 4130. I will be making some of these for my S-2 to add to and enhance the attach points currently in use. Since your need is for a shoulder harness mount you could compare them to the Pitts shoulder harness lugs which are single ear parts welded to the fuselage structure well aft of the seat. Those are .100" thick and there are two of them. I think that means they are the equivalent of your clamps made from .050" thick material. There's a limit to how much load can be transferred into a structure made from .035" tube.

    I plan on using the hydraulic press to make these (out of .063" material). I can't use heat to finish the bend on the airframe since the airplane is whole and not disassembled. .063 will be difficult enough, .090" would, I think, be impossible.
     
  16. Jun 13, 2018 at 12:28 AM #16

    pbrannan

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    Well, the 16" crossbar to which these are welded is 3/4 .049. Which is welded across a 'V' structure made out of 5/8 .035. It occurred to me that the pilot might actually be safer if the tube bent under that kind of impact, but I have not done the analysis to prove it, and probably won't. The reason for the .090 might be for the edge distance bolt load stuff or it might be that Ed had it lying around the shop and it's clearly strong enough. Anyway...

    My success in bending this stuff with heat is not great. Just never comes out well. For one, you need 4 or 5 hands unless you have it set up really well.

    I got fairly good with the drag strips, but this is a new level. Shorter part, thicker metal makes it much harder.
     
  17. Jun 13, 2018 at 12:52 AM #17

    cwilliamrose

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    Make it long to provide leverage and trim it after you get it formed.
     
  18. Jun 13, 2018 at 6:25 PM #18

    IanJ

    IanJ

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    Doing the math on this is interesting. The belts will have somewhere between 3000 and 6000 lb breaking strength (1" = 3000, 2" = 6000). AN4 bolts have a single shear strength of 3680 lbs through the full diameter (ie, not the threads), which I think means they'll withstand more (7360 lbs?) in the scenario we're looking at here (a .100" thick bracket pulling against two .090" brackets on either side, making for a double shear). The .090" tabs have an ultimate tensile strength of 6561 lbs per leg, or 13,122 lbs through both legs. I'm not sure how to calculate the tear-out strength of the bolt hole in the .090" brackets, since I don't know how the materials math works, but if it were a super simplified 1/4" x .090" section, that strength would only be 2187 lbs per leg, or 4374 lbs for both legs. I strongly suspect that number is low, probably by a lot.

    If you went with .063" brackets, you'd have a strength of 4592 lbs per leg (9185 total), and 1530 lbs tear-out (3061 total) again with my unrealistically low math for the tear-out strength. It looks to me like .063" brackets should be adequate for the job, just looking at the brackets in isolation. I would guess that the crossbar they're attached to would deform, possibly catastrophically, before the brackets or bolts let go.

    To put all this in perspective, consider that a 200 lb person is only going to put maybe 50 lbs of pressure (half their weight in the torso, split between two belts) on any given bracket at 1G, so we're looking at a 120G acceleration before the 2" belts break, and a 61G acceleration before the unrealistically low .063" bolt tear-out strength is reached.
     
  19. Jun 13, 2018 at 9:40 PM #19

    pbrannan

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    Yeah. It's overkill. I love his +.000 -.002 drilling specs on the assembly that is strong enough to crush you like an ant.

    The whole seat belt setup is not ideal. But I don't know if the fixes are worth the effort. Maybe if I was starting from scratch, I would make -428 heavier and run the belt there. That would alleviate the risk of spinal compression in the event of a hard forward impact but wouldn't be as overwhelming as some of the other fixes. I'm going to do my best not to fly it into a brick wall.

    Anyway, I spent $78 the Harbor Freight 6-ton press this morning. Nothing makes me smile like a new tool. Then i welded a "die" out of angle iron and pressed the fittings. It makes child's play out of bending the brackets. Using heat is very difficult, even on the drag strips, because the metal only wants to bend where it is hottest and it's hard to keep a large section uniformly hot. Perhaps if I went to blacksmith school...

    Based on today's experience, I heartily recommend the press. Sometimes HF is OK.

    Screen Shot 2018-06-13 at 3.28.32 PM.png


    Screen Shot 2018-06-13 at 2.50.33 PM.png
     
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  20. Jun 13, 2018 at 11:20 PM #20

    IanJ

    IanJ

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    Ah, cool. I have the 10 ton HF press. I like your solution. I would have added diagonals against the vertical pieces bending outward, but I'm not yet very experienced with steel, so I probably fall into the "overkill" camp too easily. :D
     

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