Pat's build thread

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

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  1. Jun 13, 2018 #21

    IanJ

    IanJ

    IanJ

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    Could you add an "arch" that comes to midway up the baggage door to raise the shoulder straps? It would make the baggage access ridiculous, though with a sufficiently strong latch and sturdy hinges, the arch could be part of the baggage door. ;)
     
  2. Jun 15, 2018 #22

    Larry Lyons

    Larry Lyons

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    I wondered about the bending force pushing out too. But as its a one time two use jig probably doesn't matter if they do spread a bit.
     
  3. Jun 15, 2018 #23

    pbrannan

    pbrannan

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    I am going to think about the arch after I get the seat in and see where I think it needs to be. I think what Larry is saying, is that if you hit hard enough to bend it, you have some bigger problems. The only point in raising the shoulder harness is to prevent spinal compression in a serious forward crash.

    I suppose I could put the baggage access on the side. I've thought about that. I'm all for simple.
     
  4. Jun 15, 2018 #24

    pbrannan

    pbrannan

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    In light of my simple comment above, I've been thinking about the fuel system. I was talking to a guy who owned a Marquart in the past that had a larger fuselage fuel tank and no wing tanks. Given that I'm putting an O-290 in mine, I think it would only take 21 gallons to give me 3 hours of endurance. So If I can get 5 or 6 more gallons in the main tank I would have something on the order of 24 or 25 gallons. This seems like plenty.

    Benefits: simplicity, weight, eliminate fuel management error, lower cg, fewer places to leak, less drag, nicer looks, less work, totally accessible fuel system, ability to use fuel injection without piping a return to the wing if I so desire.

    Negatives: A little less gas, possibly less passenger room, some engineering, structural issues?

    I don't really think there is a safety problem with extra fuel in the fus. Once you have 1 gallon of gas on fire in your lap you might as well have 50. Ideally, all the fuel would be in the wings, but that's not going to happen.

    I've been toying with electronic fuel injection for the engine. I know it's not possibly justifiable in any economic sense and that it's extra work and money. But it's the kind of work that I personally enjoy. The wing tanks make the fuel return difficult.
     
  5. Jun 15, 2018 #25

    IanJ

    IanJ

    IanJ

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    I think was Larry was saying was that your bending die might itself bend, but because it's only used a few times, it doesn't matter too much, responding to my comment about how I probably would have put in diagonals.

    I also have given thought to the side-mounted baggage access door. Given the shoulder belt issue (which I hadn't considered before), it makes a lot of sense to do side access to baggage, like a Stearman, and build up an arch to raise the shoulder straps to a better height. I've considered how to make the turtledeck easily removable as well, to simplify tail inspection and maintenance access. I don't imagine having the side-access door there or not would really change how the removable turtledeck would be built, though.
     
  6. Jun 18, 2018 #26

    pbrannan

    pbrannan

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    My not so great machining skills are getting me again. I am moving my seat back to it's original position. The seat frame is made of 5/8 tube and attaches in 4 places by sliding into a 3/4 inch rectangular tube.

    The original plan is to drill the rectangular tube under size and match drill the seat frame and tube when in place. Other than the fact that this wall thickness rectangular tube is no longer in stock anywhere, that's a fine plan.

    My problem is that my seat was already installed and match drilled. I now have to install it with the seat frame already drilled. So I need to make the rectangular tube match drill from the inside out.

    Does anyone have any idea how to go about this? Drawings are below. The seat frame parts highlighted with red arrows have to fit inside the -488 bracket part.

    Thanks.

    Screen Shot 2018-06-18 at 5.12.21 PM.png

    seat-attach.png
     
  7. Jun 18, 2018 #27

    IanJ

    IanJ

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    Could you weld the existing holes closed, so it can be re-drilled from "virgin" material?
     
  8. Jun 20, 2018 #28

    bneub

    bneub

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    Two possible options.
    1. Could you sleeve the seat tube, rosette weld it in and then drill a new set of holes through the sleeve?
    2. Increase the hole sizes and insert a bushing or go up one fastener size.
     
  9. Jun 21, 2018 #29

    pbrannan

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    Yeah, both are good options. What I ended up doing was matching one side hole very closely, and then drilling through the tube to the other side using the tube as a guide. The results aren't perfect but are satisfactory for the application.
     
  10. Jun 23, 2018 #30

    williamnear

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    I’ve been looking in to this also. I bought a Charger in need of quite a bit of work so I took out the old fuel tank which was highly modified to hold 29 gallons but it took up a lot of space in the front cockpit. I make a mockup of a new tank with dimensions closer to the original tank as shown in the plans. The front or rear face dimensions are 275 sq.in. I then tried different depths like 14” as described in the plans up to 19”

    The formula is 275 sq in x (depth) x .00453 gal/ cubic inch = tank volume.
    For instance: 275 x 17 x .00453 = ~21 gallons
    The 14 gallon tank in the plans appears to give a 17.4 gallon tank
     
  11. Jul 10, 2018 at 1:28 AM #31

    pbrannan

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    Anybody have a simple way to compress the landing gear shock struts? Overall length is 9.5".

    My discs are cracked and need to be replaced. I am also punching several 5/16" holes in the new discs to make them a little less stiff.

    Screen Shot 2018-07-09 at 6.46.41 PM.png
     
  12. Jul 10, 2018 at 2:50 AM #32

    pbrannan

    pbrannan

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    My thoughts on the compression struts are to buy a couple of 7/16 bolts and a couple of turnbuckles and crank it down on each side. It's crazy stiff right now, maybe because the donuts are old.

    Check out my <$49 fuselage spinner. It's stable as a rock and helped immensely with my welding. Nonetheless, I urge all Marquart builders to find a way to weld the lower pilot's seat brackets onto the cross tube before welding the cross tube in place. The uppers are easier to get to. Or maybe just become a much better welder than me.

    I'm back at work after a 10+ days of non-plane-building BS and am mostly finished putting the seat back where it's supposed to be. Two more tubes to fit and weld, then prime and paint. After that I will be rigging the plane. Something I should have done 3 months ago. Fingers crossed.

    Screen Shot 2018-07-09 at 8.40.54 PM.png
     
  13. Jul 10, 2018 at 11:58 PM #33

    pbrannan

    pbrannan

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    This is how I squeezed the compression strut. Look at those six inch long 7/16" bolts bend! These struts are stiff.

    I put in new shock discs from Univair after punching six 5/16" holes in each. I don't know how much the holes will help and haven't devised a scientific way to test. At any rate, I don't think I'll end up putting a prop in the ground:)

    When I got the project the engine was on the fuselage and plane was on the gear. I put a large guy in each seat and had them jump up and down. It didn't budge. Discs might as well have been made of concrete. I think the extremely hard gear contributes a lot to the Marquart's gear problems because it won't let the gear ride up over anything. I would like to be able to fly off of a non-perfect grass strip routinely without tearing things up. Also would like not to spend $$$ on the Belleville washers. The donuts are cheap, and in some ways failsafe.

    Even before punching the holes, I checked the old discs against the new discs with a pair of channel locks. The new discs had noticeably more give.


    Screen Shot 2018-07-10 at 5.47.54 PM.png Screen Shot 2018-07-10 at 5.48.04 PM.png
     
  14. Jul 11, 2018 at 7:09 AM #34

    IanJ

    IanJ

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    I hope the donuts work well for you. I'm cautiously optimistic about my Grove gear plan, since I can design the fuselage from day one for the new gear type.
     

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