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  • #61
    Awesome Write Up, Nev! Wow!!! You guys are very creative and I learned a lot from your testing. Our community will attract and thrive with material like this.

    I'm thinking outloud.

    -The lower cap body control with the Engagement Pin for positive control the O-ring crush is awesome. I had been accommodating it, but never saw it as a risk like you did. You two codified, exposed and fixed it. Great work.

    -You say you removed .005" from the shank surface where the O-rings ride. Would you declare a shank dimension for us? I suspect that slight variations exist (change in venders?)



    Brooks Cone
    Southeast Michigan
    Patrol #303, Kit build

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    • Nev
      Nev commented
      Editing a comment
      Hey Brooks, Thanks. Mostly Grahams work of course.
      Yes I'll get a shank dimension for you. (Left my calipers at the hanger!)
      Last edited by Nev; 08-03-2022, 05:05 PM.

    • Nev
      Nev commented
      Editing a comment
      We discovered today that the shanks are not identical in diameter. We have 3 that measure approximately 34.35mm. The one we altered was slightly wider initially, and Graham has now turned it down to 34mm. If we turn it down any further it won't have enough holding friction. We are going to try a couple of other ideas, then will report back.

  • #62
    Can anyone confirm what material the original O rings are ?
    Nev Bailey
    Christchurch, NZ
    Builders-log
    YouTube Bearhawk Blog

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    • Mark Goldberg
      Mark Goldberg commented
      Editing a comment
      They are called VITON o rings here.

  • #63
    OK, I finally took the fuel caps out of the bubble wrap. I assume the large O-Ring goes on the position I put it, it looks like the white nylon washer goes between the two pieces. Where does the smaller O-Ring go?

    8997AE59-EDC7-4B37-894A-4F1612764805.jpg

    It seems there is a gap between the O-Ring and the two different threaded pieces.

    N678C reserved
    Revo Sunglasses Ambassador
    https://www.youtube.com/channel/UCQ0...tBJLdV8HB_jSIA

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    • #64
      See if this helps.....

      703F3C6B-0A26-4EA3-95D9-A3FF357EDA21.jpg
      Nev Bailey
      Christchurch, NZ
      Builders-log
      YouTube Bearhawk Blog

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      • #65
        My wings are still in the crates (coming out in a few months), but this thread got me curious about the fuel caps. After Nev posted the photo the design makes perfect sense. Of course I am clueless having not used one yet, but through some trial and error I would think that one you got the proper index it is a fool proof design. The only think I am surprised a bit about is that there is not a type of “Y” hanging down from a chain in the tank to retain the cap during refueling. IF someone was so inclined it would be an easy addition. But finding the correct cap index and then possibly tweaking the O-Rings the system should be damn good
        N678C reserved
        Revo Sunglasses Ambassador
        https://www.youtube.com/channel/UCQ0...tBJLdV8HB_jSIA

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        • Mark Goldberg
          Mark Goldberg commented
          Editing a comment
          There is a little hole at the bottom for a cotter pin that keeps someone from unscrewing it enough to drop the bottom into the tank. The fuel caps were not originally designed with the hole in the bottom. We added 1/4" of length so there was room for that hole for the cotter pin. Bob agreed to let us add the 1/4" of length even though it adds weight.. Mark

        • Utah-Jay
          Utah-Jay commented
          Editing a comment
          Mark Goldberg I saw that hole and the cotter pin makes a lot of sense, thanks!

      • #66
        I've been thinking about this and wondering why I've never lost a cap. There has to be something uncommon between those that have lost caps and those that haven't.

        My procedure for refueling is basically:

        1. Twist cap 180 deg to loosen. Always 180 deg so I know where to position the cap so it faces forward when tightened.
        2. Gently rock cam back and forth while lifting up to remove the cap.
        3. Add fuel to the bottom of the filler neck. I don't like the cap sitting in fuel, it happens sometimes but I prefer it not.
        4. If the cap was difficult to remove then I take a couple of drops of oil from the engine breather tube and apply it to the o rings.
        5. Install cap with vent facing to the rear and the top lip against the filler neck.
        6. Tighten cap. Should be the same 180 deg turn to make it tight and clocked correctly facing forward.

        Perhaps some fill the tanks fuller and the hydraulic pressure from fuel expansion pushes the caps out. The seems pretty unlikely to me as the fuel would just flow out the vent holes unless it expands quickly or the vent is constricted.

        The only issue I've had with the caps is the threads on one galled. I was able to get the cap off, chase the threads and then applied anti-seize to the threads on both caps. No issues since.
        Scratch Built 4-place Bearhawk. Continental IO-360, 88" C203 McCauley prop.

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        • Bissetg
          Bissetg commented
          Editing a comment
          Hi Whee, my experience was pretty similar, except like Nev and others I was having to pry the caps off with a screwdriver. I think Marks advice of turning the shaft of the cap down a sniff would have helped this but both Nev and I were advised to lube the caps with EZ lube which we did. It made the caps much better to put on and off but reduced the locking friction in the filler neck. In hindsight I probably overfilled the tank (I usually leave a little headroom in the tank) and with a bit of turbulence I suspect the slosh hydraulics the cap out. It’s interesting to see that others have been working on solutions to this problem in the past, I’m sure we will soon get at least one and maybe more ways to address this. Until it happened to me I thought Nev hadn’t put his cap on properly.

      • #67
        This is interesting Whee. I never had any issue with my caps staying on initially. The problem was I couldn't get them off. I was having to use a screw driver. It was also difficult to install. I could only ever get a 90° twist out of the threads (not 180°). Sometimes it would turn further, but that turned out to be the lower body turning with the threads and wasn't actually tightening it further.I suspect that the small variation in shaft size might be affecting how consistent they are to do up.

        It was because of the difficulty installing and removing it that I added a lubricant to the O rings. But as a result, the lower body spins even more. Grahams idea of adding a pin completely stops this and a 180° twist always provides exactly the same amount of compression every time. Currently we have a cap that is much easier to install and remove, and can be tightened to remain secure. It does need to be tightened properly, but the force to remove it now is very similar to the original fuel caps with engine oil on the rings.

        One thing I discovered yesterday is that the addition of fuel on the O rings after installation and tightening, significantly reduces the locking friction. It appears that the lower ring is keeping the upper ring relatively dry.

        Graham has ordered some more tooling for his lathe and next week we are going to try a couple of small changes.

        So far what I've learn't Is that every change we make causes a couple of other things to change. There seem to be pros and cons to each possible solution. One example is I made up some locking tabs so that a 30° twist of the cap itself locks the tabs into place, before tightening the threads. It stops the cap coming off mechanically. However when fixing the tabs to the cap, you need to have them in the correct spot so the threads can then be tightened the right amount. If the O rings subsequently compress over time, the vent will have to turn past the forward position to fully compress the rings.
        Nev Bailey
        Christchurch, NZ
        Builders-log
        YouTube Bearhawk Blog

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        • #68
          Originally posted by mbaerobat View Post
          I have had a few caps disappear in flight.
          The method that seems to be working for me is the application of some fuel to the O rings when placing the caps in the neck and then tightening the cap tightly using a tool that I made.
          Finger tight doesn’t seem to do the job.
          The tool is made from UHMW plastic but my original was made from hardwood.
          Haven’t lost a cap since. Still carry a spare cap just in case….
          I'm going to try the tool idea. We've currently got a cap that installs and removes very easily, if a 180° turn is used. But we're not sure if that's tight enough. The tool might be an easy way to solve that.

          I'm thinking especially if the tool had a bottle opener on the other end. Every self respecting Bearhawker would want one in their survival kit
          Nev Bailey
          Christchurch, NZ
          Builders-log
          YouTube Bearhawk Blog

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          • robcaldwell
            robcaldwell commented
            Editing a comment
            I used the tool method. A flathead screwdriver to get the cap started so I can rock it back and forth for removal. Then I use an aluminum adjustable wrench (fuel fitting tool) to tighten the cap back on. 1/2 turn doesn't get it for me, so I go 3/4 turn for a snug fit.

        • #69
          Actually I've got 3 fuel caps sitting in front of me and all 3 are different. The smaller vent hole size has an inlet area of 1.75 ²/mm. The larger vent hole size has an inlet area of 9.0 ²/mm.

          5CE3D0D0-F696-4C87-87A1-8E61ED6FCC60.jpg

          A45853DB-83F0-4BC5-8EDB-6A492AF54CFD.jpg
          Last edited by Nev; 08-06-2022, 01:29 PM.
          Nev Bailey
          Christchurch, NZ
          Builders-log
          YouTube Bearhawk Blog

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          • #70
            Rob we now have them working so they can be dropped into the filler neck very easily, and removed easily with one hand. I'll post a short video once we're confident they're working consistently. Using a tool to tighten and loosen certainly ensures they're tight enough. Having a pin to stop the lower from rotating inside the neck makes a huge difference.
            Nev Bailey
            Christchurch, NZ
            Builders-log
            YouTube Bearhawk Blog

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            • #71
              Here's a short video showing where we're at with the fuel caps.



              This isn't a mechanical lock, and it does benefit from using a tool to help tighten and loosen the cap. However, they are now very easy to install and remove, and appear to be quite secure in position.

              We also think that when mechanically locking caps are available they should prove extremely popular.

              We had hoped to avoid specialist machining, but after trying so many ideas and combinations, the solution we've got at this stage used a lathe to reduce the shank size from 34.35mm to 33.35mm, size -383 O rings, and the installation of a pin to prevent the lower body from turning. The pin made a significant difference, and would be a great addition even if you didn't change anything else. When loosened, the fuel cap inserts easily inside the filler neck with no resistance, and is lifted out with no resistance. We expect that after sitting in place for a week or two, there may be some slight friction to remove the cap, but it should be minimal.

              Obviously time in use will be needed to highlight any issues. I'm very interested to see if there's any changes with the larger vent hole and the increase in tank pressure. I plan to test them inflight later this week.
              Last edited by Nev; 08-06-2022, 09:01 PM.
              Nev Bailey
              Christchurch, NZ
              Builders-log
              YouTube Bearhawk Blog

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              • #72
                Kevin kindly used my BH as a test bed for his personally designed fuel caps for the last several years, including several mods which improved an already functional design.

                I cannot describe the pleasure of refueling now as opposed to four letter word blood pressure raising experiences with the original. I did lose two of the old ones.

                Kevin has a box of the fuel cap parts but no time to organize assembly or order parts from machine shops. Full attention goes to his aircraft completion.

                It will be worth the wait and he should be flying in time for Bob's BBQ.

                Scott Williamson
                924PL

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                • Nev
                  Nev commented
                  Editing a comment
                  Yep looking forward to seeing a couple of Kevin's fuel caps!
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