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Thread: 109JB's Kitfox IV rebuild

  1. #21
    Senior Member t j's Avatar
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    Default Re: 109JB's Kitfox IV rebuild

    The damage in the photos looks to me like it ended up on it's back. I would stretch a string on all the struts and wing spars to make sure nothing is bent there. Also, you can't change the dihedral much once the attach holes are drilled in the wing spars.
    Tom Jones
    Classic 4 builder

  2. #22
    Senior Member 109JB's Avatar
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    Default Re: 109JB's Kitfox IV rebuild

    Yes it was on its back. That was said in the first post. The only wing damage was one broken tail on a top leading edge short rib. Everything is straight now. This problem existed from the builder as evidenced by the modified trailering strut for that side. It doesn't need much change in dihedral and even if it did one could always fabricate new internal reinforcement plates and rivet them in. Would only need to do the bottom plates. I'll find out if the dihedral is off once the weather is fit to put the wings back on.
    John Brannen
    Morris, IL
    Sonerai IIL (Single Seat)
    Kitfox 3/4 1050 - Rotax 582 (Back Flying and sold)
    Kitfox IV 1050 - Rotax 582 (sold)
    Kitfox IV 1200 Speedster - Rotax 912 UL (project)
    Piper Twin Comanche (Sold)
    Glasair 1 FT (Waiting to start)

  3. #23
    Senior Member jrevens's Avatar
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    Default Re: 109JB's Kitfox IV rebuild

    In analyzing this, one thing that would cause the "misalignment" when folded is a slight difference in the angle or position of the tube that is welded to the spar carry-through tube of the fuselage, that the spar attachment bolt goes through. Just the tiniest misalignment of that tube (the holes drilled in the carry-through for it) when it is installed/welded will result a considerable misalignment out at the wingtip when folded, regardless of how correct the dihedral is in the flying position.
    Last edited by jrevens; 04-15-2020 at 08:50 PM.
    John Evens
    Arvada, CO
    Kitfox SS7 N27JE
    EAA Lifetime
    Chap. 43 honorary Lifetime

  4. #24
    Senior Member 109JB's Avatar
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    Default Re: 109JB's Kitfox IV rebuild

    Lets see if i understand what you are saying correctly. I think you are saying that if the fuselage mounted tube the rear spar bolt goes through is rotated CW or CCW when viewed from the side of the fuselage, that this will affect the height of the wing tip when folded.

    If I am understanding you correctly I will have to disagree. While that may be true if the rear spar was the only pivot point, it isn't. The lower strut mount on the fuselage is also a pivot point. So when folded the strut is still holding up the wing. The three points that are of concern here are the rear spar attach, the lower fuselage to strut attach, and the strut to wing attach. The triangle formed by these 3 points is very stiff and the mechanical advantage in the strut/wing setup will far outweigh any bending moment influence that bolt going through that short 2.5" long tube at the rear spar attach can muster. So in essence if that tube were misaligned/rotated, folding the wing could put undue stress on the spar bolt, reinforcing plates, etc. but it would not have any appreciable affect on the tip position.
    John Brannen
    Morris, IL
    Sonerai IIL (Single Seat)
    Kitfox 3/4 1050 - Rotax 582 (Back Flying and sold)
    Kitfox IV 1050 - Rotax 582 (sold)
    Kitfox IV 1200 Speedster - Rotax 912 UL (project)
    Piper Twin Comanche (Sold)
    Glasair 1 FT (Waiting to start)

  5. #25
    Senior Member jrevens's Avatar
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    Default Re: 109JB's Kitfox IV rebuild

    You’re right, John. I was obviously not thinking very clearly. If the 2 pivot points on the fuselage are not in exactly the same alignment with each other, comparing the right side to the left side, or the fuselage & tail structure isn’t straight, or the wing dihedral and washout isn’t exactly the same, etc., then the position of things when folded may not be in alignment & where you want them to be. You & I and everybody else knows this, so I don’t know why I was thinking the way I was. Sorry about that!
    John Evens
    Arvada, CO
    Kitfox SS7 N27JE
    EAA Lifetime
    Chap. 43 honorary Lifetime

  6. #26
    Senior Member t j's Avatar
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    Default Re: 109JB's Kitfox IV rebuild

    Sorry, I missed that you said in the first post that it nosed over. Blame it on the 70's. I'm 70 now.

    When I started rigging the wings on my classic 4 the instructions said to make sure the wing tips were even when folded. I chased that for two weeks. The best I could do was get the wing tips to about an inch and a half from even when folded back. I studied the situation for some time and finally observed that the rear wing spar to fuselage attach bolt and the lower strut to fuselage bolt formed the pins of a "Hinge" that the wings swing on when folding back.

    To check the alignment of the lower strut attachment bolt holes I leveled the fuselage and dropped a plumb bob with the string running through the top carry through wing attachment lug. On the wing with the high tip, the plumb bob point centered in the lower strut bolt hole. On the wing with the low tip, the point of the plumb bob was about 1/4 inch forward of that bolt hole. It then became clear what was going on. One wing hinge was vertical and one was tilted a little off from vertial.

    I called the old Skystar factory and asked what I should do. He said to just rig the wings when spread and not worry about the uneven tips. Mine was not a speedster so dihedral provided plenty of clearance from the horizontal stabilizer.

    Does this make any sense?
    Last edited by t j; 04-16-2020 at 07:00 AM.
    Tom Jones
    Classic 4 builder

  7. #27
    Senior Member 109JB's Avatar
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    Default Re: 109JB's Kitfox IV rebuild

    Quote Originally Posted by t j View Post
    Does this make any sense?
    Sure does. I have a IV-1050 and I know that one wing sits a little lower than the other when folded too, but since the long wing IV has more dihedral it still clears by plenty. I had thought that maybe the lower pivot was too far forward and was going to check. Not sure anything could be done about the short of welding on a new strut mount to the fuselage. That would probably result in the strut not bent right and having to make a custom length set of struts. Lots to think about. First thing will be to get the wings back on and measure a ton of stuff. I probably should just leave it alone but it's supposed to be a folding wing airplane so I'd like to fix it. We'll see.
    John Brannen
    Morris, IL
    Sonerai IIL (Single Seat)
    Kitfox 3/4 1050 - Rotax 582 (Back Flying and sold)
    Kitfox IV 1050 - Rotax 582 (sold)
    Kitfox IV 1200 Speedster - Rotax 912 UL (project)
    Piper Twin Comanche (Sold)
    Glasair 1 FT (Waiting to start)

  8. #28
    Senior Member 109JB's Avatar
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    Default Re: 109JB's Kitfox IV rebuild

    I was looking through the paperwork I got with the airplane for something else and happened to see notes from the second owner who re-did the airplane back in 2007 and one of the entries read "Why doesn't right wing fold correctly? So it seems that the right wing didn't fold right way 13 years ago either. I know that guy so I'll give him a call and see if that note was referring to this issue (I think it must be) and if he ever found anything out about it.
    John Brannen
    Morris, IL
    Sonerai IIL (Single Seat)
    Kitfox 3/4 1050 - Rotax 582 (Back Flying and sold)
    Kitfox IV 1050 - Rotax 582 (sold)
    Kitfox IV 1200 Speedster - Rotax 912 UL (project)
    Piper Twin Comanche (Sold)
    Glasair 1 FT (Waiting to start)

  9. #29
    Senior Member 109JB's Avatar
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    Default Re: 109JB's Kitfox IV rebuild

    Having completed my initial assessment of the airplane I decided it was time to get the shop ready and to do more disassembly. I'll have some pictures of the airplane later, but wanted to comment on a practice that just flat out puzzles me. I even went into the builders manual that came with the airplane and it is in there so it isn't a one-off builder screw up. What am I talking about? Rivets in steel tube structure. Now I'm not talking about cases where there may very well be a valid reason for doing it. I'm talking about doing it just because it is easier.

    For example, the firewall on the Kitfox IV at least, is riveted to 3 different tubes at the firewall station using aluminum pop rivets. There are probably 30 rivets for that alone. That is 30 places for potential water intrusion and if water does get in it has no way to get out. Can you say "rust". Sure, the firewall needs the rivets to hold the different pieces of the firewall sheet metal together, but it doesn't need to be riveted to the tubes. It can't go anywhere because it is sandwiched between the engine mount and the fuselage and any more security it needs can be handled with a few tabs. I've now have all of those drilled off rivet tails inside of those tubes and can't get them out. At least not easily. I'm going to wind up welding all of those holes shut and putting on maybe 6 tabs for the firewall security.

    Another example is a hole drilled into the top of door sill tube. What is it there for? A little wire clip that you can drop into the hole to keep the door open about 3 inches at the bottom. Ok fine, but it is also about 3/16" diameter and in the top of the tube. There is obvious rust around the hole telling me that water has had a chance to get in there and there isn't any other hole at the low point for the water to get out. I'm seriously debating whether I should just replace that whole tube or at least cut out the rear section of one to see if it is rusted inside.

    I could give several more examples from my airplane from nose to tail but you get the point. I would much rather see a screw and a little sealer that a rivet. Aluminum pop rivets have a mandrel that many times falls out leaving a hole and they also work loose. Probably 1/3 of the rivets I removed were loose.

    From my perspective drilling holes into steel tube structure for no good reason is an unnecessary practice. I previously built a Sonerai IIL and when I welded that fuselage it wound up with exactly 4 holes that go through into the interior of the tube structure. Those holes were put in specifically for a path to introduce preservative coating to the inside of the tubes. These holes were then plugged with sheet metal screws and a sealer (they don't leave tails inside if removed.). It can be done, and in my opinion should be done this way if possible.

    OK. I'm coming down off of my soapbox now.
    John Brannen
    Morris, IL
    Sonerai IIL (Single Seat)
    Kitfox 3/4 1050 - Rotax 582 (Back Flying and sold)
    Kitfox IV 1050 - Rotax 582 (sold)
    Kitfox IV 1200 Speedster - Rotax 912 UL (project)
    Piper Twin Comanche (Sold)
    Glasair 1 FT (Waiting to start)

  10. #30
    Senior Member 109JB's Avatar
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    Default Re: 109JB's Kitfox IV rebuild

    Have had other things going on but did receive my Garmin stuff and have had a chance to play with the G5. Super easy to get going in a basic sense. 2 wires and an old serial port plug got it going. I'll be putting it in with a GMC507 autopilot controller, and servos, so I want to be able to pipe in navigation data so it can fly a planned route. In that vein, I played around with a $5 bluetooth module, and a $2 TTL to RS232 module, and was able to get Avare on my Android phone talking to the G5 without any problem. You can tell that the nav is working in the picture below because the CDI needle on the G5 has appeared. Without a nav signal the CDI isn't there. There is also a pic of my current plan for the instrument panel. I may or may not mount the standard airspeed indicator. Also, to answer the inevitable questions, the green LCD below the G5 will be an engine monitor that I will build myself, and the green LCD on the right side of the panel will be a home-brew instrument that has the basics in digital format in case I want to fly from the right seat.

    IMG_0806.jpg

    Instrument panel.jpg
    John Brannen
    Morris, IL
    Sonerai IIL (Single Seat)
    Kitfox 3/4 1050 - Rotax 582 (Back Flying and sold)
    Kitfox IV 1050 - Rotax 582 (sold)
    Kitfox IV 1200 Speedster - Rotax 912 UL (project)
    Piper Twin Comanche (Sold)
    Glasair 1 FT (Waiting to start)

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