IanJ's Marquart Charger Build Thread, part 2

Discussion in 'Marquart Charger' started by IanJ, Aug 3, 2018.

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  1. Sep 19, 2018 #101

    IanJ

    IanJ

    IanJ

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    Thanks Randy, that's good to hear. I worry a little bit about the burned-looking sections just inboard from the weld bead. Up-thread someone mentioned I might be using too much heat, but perhaps that's just what gas welds look like.
     
  2. Oct 3, 2018 #102

    IanJ

    IanJ

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    Many thanks to Alaskamech, who was kind enough to help me get drag strips cut today. And who pointed out that switching to drag wires would be about half the cost of doing it the Marquart Way. :D With this, I think I've got all the "parts" I need to build the wings. Probably have to spend ~30 hours making these drag strip blanks into actual parts, but it's all part of the fun. (No picture taken; imagine a pile of about 40 pieces of .063" 4130 that are 36" long and half an inch wide.)

    The plans call for the edges of these things to be polished without specifying quite what that means. Polished like free of noticeable scratches, or polished like I can see my face reflected in them? I know it's to prevent stress risers, but I've never been clear on how finicky you have to be about this particular operation.
     
  3. Oct 3, 2018 #103

    pbrannan

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    Let me know if you need individual drag strip lengths. I think the plans are off on a few. It’s nice to get them right the first time.

    Or just wait till you are putting you wing together and measure.
     
  4. Oct 4, 2018 #104

    IanJ

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    I'd appreciate it if you wanted to send me your lengths. I'm planning to build the drag strips before assembling, though maybe that's not a great idea if the plans are inaccurate. Maybe I should just build the folded-over end of each of them and leave them too long, for eventual measurement and installation. The non-folded end will be much less trouble to assemble one at a time.

    dragstripsxcf.png
     
  5. Oct 4, 2018 #105

    IanJ

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    Finally got back to the project tonight after a couple weeks not having time. It was a silly task, but I think worthwhile: I faced all the bushings I welded into the compression tubes, so they'll sit perfectly flat against the brackets when they're installed in the wings. Gotta love having a lathe.

    [​IMG]
     
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  6. Oct 4, 2018 #106

    pbrannan

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    I would advise doing the loop and cut first then waiting. I’ll PM you my lengths.
     
  7. Oct 4, 2018 #107

    Kiwi

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    Polished in this case means rubbed with some sandpaper. If I was making these, with a fine file of large dimensions, I would file the sheared edge until the "sheared" appearance is gone, run along the corners to remove the burr and then give them a bit of a polish with something like 240 grit paper. Frankly, if you don't end up with chatter with the file, that would be good enough, but the polish is probably worth it to say you've done a nice job. Then paint, because corrosion will just make it rough again.
     
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  8. Oct 4, 2018 #108

    taff

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    Ian.
    In other parts of the world, polish means different to the US. Polish in the US means compounding and/or bringing the surface up to a high gloss (such as polishing and waxing the car)
    In Holland , maybe Germany and other parts, polish means sanding something, usually with something fine like P400 and above. Sanding in this case would be P180 grit and below.
     
  9. Oct 4, 2018 #109

    Kiwi

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    Eric & Ian,
    Polish is a common term used in engineering and it does have a different connotation than polishing a paint surface. The techniques used and surface finish expected will differ depending upon the application. The objective is to remove stress raisers. These drag / anti-drag strips are not highly stressed and 4130 isn't that notch sensitive, so a surface finish to match that application is appropriate.
     
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  10. Oct 4, 2018 #110

    IanJ

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    Thanks Andrew, that's what I figured. I have some lovely new Swiss pattern files that should do the job well. The strips are a tiny bit oversize in anticipation of the polishing operation.

    I keep thinking that switching to wires would be so much easier. The chief advantage I've thought of for the strips-and-turnbuckles approach is that if you need to adjust the tension once the wing is covered, you need one fewer access cover per wire with turnbuckles. I suppose you don't have to worry about the rolled-vs-cut threads "controversy." I assume that much like Pete Bowers and his Fly Baby, Ed Marquart must have been sitting on a huge pile of surplus turnbuckles at a few bucks a pop, and neither anticipated that you might be spending $30-50 per turnbuckle in the future (or that anyone would be building these things 50 years later).

    Unrelated, but I read "Biplane" by Richard Bach recently, and it struck me how strongly he considered his 1929 Parks biplane to be ancient, at 35 years old. It was, to be sure, much older than new planes of the era with that much progress having been made, but the different perspective was oddly jarring. Perhaps it's that we still look at a 1965 Cessna 172 and think it looks pretty much like a 172 from 2018. Nothing like the jump from biplanes to "modern" monoplane trainers and cruisers. I suppose the design of modern new-design planes like jet fighters or jet transport planes doesn't have much reflection back on the GA fleet, compared to the way WWII revolutionized airplane design in general.
     
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  11. Oct 5, 2018 #111

    pbrannan

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    It’s funny. I started out thinking that the strips were a good solution. I still think that they get the job done. But as I’ve learned more I’ve come to the conclusion that they are unnecessarily difficult and expensive for most homebuilders.

    How to bend a nice loop? How to cut a reasonable 070 slit in a home shop? How to get the lengths right? Leave enough room on the doubler side for safety wire? And safety wiring 48 turnbuckles takes some time as well.

    In my case I started this because I wanted to learn. Have to keep reminding myself of that.
     
  12. Oct 5, 2018 #112

    IanJ

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    The more I think about it, the less I understand the choice of drag strips over wires. It's not like 4130 rod/wire wouldn't have been available, and cutting threads is cutting threads, that's very homebuilder-accessible. The only thing I can think is that he had a bucket full of AN-150-16S turnbuckles (or they were the cheapest option at the time), and wanted to figure out a way to use them. Or maybe he had some strong aversion to cut threads in 4130 rod, I know the contention is that they're not as strong as rolled threads.
     
  13. Oct 5, 2018 #113

    pbrannan

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    Doesn’t really matter if they are “not as strong” as long as “how strong they are” can be measured and they are strong enough.

    At any rate, I made it through the drag strips and am pretty sure they’ll do the job for a year or two.

    Changing this would be high on my list for updating plans. Strengthening landing gear would be tops. Easier to build struts way up there too.
     
  14. Oct 5, 2018 #114

    IanJ

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    Yeah, I'm 60% of the way to having drag strips (if you count spending money as being part of the path), so I'll just keep going with that. I don't mind having more brainless work to do right now, so that works fine for me.
     
  15. Oct 7, 2018 #115

    IanJ

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    In the absence of a proper metal brake, I decided to build a bending jig for the drag strips. I probably went a little overboard with the materials, all 1/4" thick mild steel. I definitely do not like fitting up the AW208 tip and firing up the jet engine howl of that thing, and having a weld puddle 1/2" across is frankly kind of freaky. Still, it'll be very nice when it's all done. No pictures yet, as it doesn't really look like anything yet. Hopefully tomorrow I can actually get it finished. Maybe the huge ingots of steel will have cooled down enough to touch by then. :D
     
  16. Oct 8, 2018 #116

    Lotahp1

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    Interesting approach to a fairly easy task for sure. I’m still a huge fan of the Starduster Too 4130 tubes as drag/antidrag “wires”. Once bolted up there is zero chance of loosening, cracked corner blocks, no zillion $$$$ items needed or crazy tubes inside of tubes with welded in nuts. BUT maybe there is a reason I’m missing such a design isn’t used more often...as I’ve only seen it on Stolp designs? The weight has to be higher than regular “Pitts” style solution, but lighter than the Charger solution.
    I’m about to assemble my lower RH wing on my Starduster Too and could weigh all the items...I’d just be curious what the chargers all weigh ?

    I assume the tube solution doesn’t work here because of the wing sweep?

    Sorry to get off base...just trying to learn the why’s of design. You are doing an AMAZING job! Your plane will be a show stopper I can tell. With tolerances down to .000 I can tell you mine does not have! And it seems to be ok. Keep up the great work!

    Lastly, I’m about to buy some bottles for my Smith torch I got from NDTOO awhile back (I bought a good set of regulators from miller at Oshkosh last year) what size bottles do you recommend? I’d love to see a video of you welding...as a rookie, your welds look VERY good...even for a long time welder they look good.
     
  17. Oct 12, 2018 at 6:46 AM #117

    IanJ

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    Thanks for all the kind words!

    For the drag/anti-drag solution, I suspect that the Charger-style strips are roughly on par with the Pitts/Eagle style, probably 10% heavier with the turnbuckles. I'm not familiar with how the Starduster does it, but I'd assume it would be a similar weight -- they all design for about the same pull (or, I suspect, push-pull on the SDII). If one was vastly better than the others, everyone would do it. I think the Charger has the system it does with split compression tubes to deal with imprecise placement of angle blocks resulting in slightly variable tube lengths. The drag strips are a bit of a mystery to me, compared to threaded drag wires. I just finished my bending jig and it works like I'd hoped it would (but it's ugly as all get out). I'm seriously considering switching to drag wires, though, as the strips are going to take dozens of hours to finish compared to wires. I assume that drag tubes wouldn't work in the Charger for the same reason the compression tubes are split -- unpredictable lengths.

    My welding setup is the Smith Airline torch (from Ebay), the regulators that came with the torch (had them checked out by a local shop before using them), super skinny kevlar hoses (highly recommended, they complement the light weight torch very nicely, makes it much easier to handle), a ~30" tall acetylene cylinder, and a ~45" tall oxygen cylinder. I don't know the size names. I picked the bottle sizes by chatting with the salesman at the welding store: I told him what I was doing (fuselage, .035" wall tubes, etc.) and he recommended a couple sizes that he thought would work. I think I picked the one either in the middle, or slightly on the large size among his picks. I actually think I got way too much O2, because his recommended size was taking into account a bunch of oxy cutting, which I have definitely not been doing -- I tried cutting one of my 1/4" thick pieces with the torch, shot fat hunks of red-hot metal everywhere, started a fire (fortunately confined to a bucket and quickly put out), and had a really horrible jagged cut. I decided that was not for me, and used the angle grinder to cut the rest of the pieces. I need to get the $250 HF horizontal bandsaw, that's the right solution for what I'm doing. I'm a wilting flower in the face of high-BTU torch work, as it turns out. The .035" welding is much more my speed.

    I can tell you that not all of my tolerances are in the thousandths of an inch. I'm trying to be as accurate and precise as possible, but particularly the wooden ribs are kind of variable. I think it's a matter of picking your battles. Holding everything to a .001" precision will definitely make the build take a lot longer, so I'm only being a stickler in places where it doesn't add much to the time I'd have to spend anyway.
     
  18. Oct 12, 2018 at 6:53 AM #118

    IanJ

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    Here's the horrible bending jig. The thing in the foreground is the pressing blade (with a hunk of 1/4" round welded to the edge for a high quality 1/4" curve), and it fits down into the slot of the contraption on the left. Those jaggy verticals align the drag strip so the bend is pretty well square, and keep the blade from falling over when pressure is applied. It works based on a few test bends, but it's only part of the solution. I'll also be employing the vise to finish the bend, with another hunk of 1/4" round in place to keep the hoop open as the strip is bent closed. IMG_20181011_195150.jpeg
     

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