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  • Elevator hinge design

    Does anyone have any insight into why the bearhawk elevator hinges are designed as they are?

    Was talking with another builder tonight and we got on the topic of lubricating the hinges. I was asked why not just use a Piper style hinge? While that seems simpler and easier to keep lubricated, it made me ask a question I can't answer: Why did Bob use this hinge design?

    Thanks.

  • #2
    I don't know why Bob designed it that way but I have an opinion.
    1. The strap hinge is fairly easy to fabricate. Good for the home workshop
    2. It shares a bolt through the spar with the tail brace wires.
    3. broader bearing surface area, very strong
    4. tighter gap
    5. Piper style not fun to keep straight when building from scratch.

    Having built a Pitts Special years ago I was familiar with the use of this type hinge and had over 800 hours on the airplane with no appreciable wear. Hard to argue with a successful design.
    I didn't install zerk's on mine. I will maintain through an 1/8" oil hole.

    My 2 cents worth.
    Kevin

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    • #3
      Mine also has a hole for oiling. Works well.

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      • #4
        Your question created curiosity, so I had to research what a Pipe Hinge looked like. I found a photo, and this statement made by a builder of a different (inferior type) experimental tube fuselage aircraft.

        After building these (Piper) hinges I found what I think would be a much better way. I don't have much experience building hinges like this i.e. Piper type with hinge pins, I've always used the Pitts style which tucks the elevator stab in much closer to the horizontal stab.

        The gap between the stabilizer surface and the control surface is reduced by Bob's hinge design.
        Elevator hinge pdf.pdf

        PS. Teach me how to include an attachment so that it appears in my response rather than requiring a reader to download it.
        Attached Files
        Last edited by Bcone1381; 12-10-2016, 09:52 AM. Reason: Added PS.
        Brooks Cone
        Southeast Michigan
        Patrol #303, Kit build

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        • #5
          I figured the design has less gap and that the move away from zerks to the oil hole was likely to avoid grease stiffening up to much in the cold. It is harder to cover around. We used some light aluminum to support the fabric edges along the hinges.

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          • #6
            I see everyone is referring to that hole in the hinges as an oil hole. What is the thinking behind using oil?

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            • #7
              Originally posted by Battson
              I see everyone is referring to that hole in the hinges as an oil hole. What is the thinking behind using oil?
              I'm pretty sure I read to use oil in a newsletter but maybe not. I know I read it somewhere. Never made any since to me. I plan to use a syringe and grease, thanks for solving that one for me.
              Last edited by whee; 12-12-2016, 05:10 PM.
              Scratch Built 4-place Bearhawk. Continental IO-360, 88" C203 McCauley prop.

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              • #8
                I thought I read about someone using oil and having their hinge seize up, was that in the Safety section earlier this year?

                My IA recommended I use Grease 22 for the hinges. Plus I am used to greasing stuff like that, from working with tractors in my formitive years. So I just always assumed they were grease holes. Thus I was a bit surprized to see everyone referring to them as oil holes, I wonder if I've missed a notice or something.
                Last edited by Battson; 12-12-2016, 05:51 PM.

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                • #9
                  I don't remember the section but it was Jared that had his rudder hinge get stiff.
                  Scratch Built 4-place Bearhawk. Continental IO-360, 88" C203 McCauley prop.

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                  • mpillor
                    mpillor commented
                    Editing a comment
                    Think I remember that was rust in Jared's rudder.

                • #10
                  I think FLUID FILM is an ideal product for a hinge lubricant.

                  Oil & Petroleum Grease based products all have some evaporative properties, from WD-40 to Wheel Bearing Grease. When evaporation takes place, it changes the properties of the product. Things tend to become sticky, and gum up over a period of time. This collects dirt, and I imagine the lubrication properties get sacrificed. I have an old grease tub in my garage and the stuff grease on the outside is sticky, stiff, and yucky due to its evaporation. Its almost like soft wax.

                  Ten years or so ago, an A&P/IA introduced me to Fluid Film. I am just a user of the product, passing along my experience.

                  Fluid Film is a liquid penetrant/lubricant used for corrosion prevention in corrosive marine environments. It is not Petroleum based (its Lanolin based from Wool) with no solvents to evaporate. So it will not become sticky, it will not gum up, stays wet over a long period of time, It will not evaporate or dry from the surface. FLUID FILM will leave a wet, non-drying film, that will provide long term corrosion protection on all metals and superior lubrication for all moving parts. Its Non-silicone, displaces water from metal surfaces, non toxic, non-irritant. I used it during the annual of my C-140, and I still had a wet surface on the chain that drove the elevator trim the next year.

                  It not available at my local auto-parts store, but the John Deere dealer carries it.

                  Get technical information and MSDS sheets for aerosol and non-aerosol versions of our flagship Fluid Film product.
                  Brooks Cone
                  Southeast Michigan
                  Patrol #303, Kit build

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                  • #11
                    Originally posted by Bcone1381 View Post
                    Oil & Petroleum Grease based products all have some evaporative properties, from WD-40 to Wheel Bearing Grease. When evaporation takes place, it changes the properties of the product. Things tend to become sticky, and gum up over a period of time. This collects dirt, and I imagine the lubrication properties get sacrificed. I have an old grease tub in my garage and the stuff grease on the outside is sticky, stiff, and yucky due to its evaporation. Its almost like soft wax.
                    This is true, and it is important to lubricate every 100hrs at least. I like to pressurise the new grease with a syringe / grease gun and force the old grease out. I am just about finished with my 500hr check, and one interesting finding - resistance felt in the joystick was noticeably reduced when I lubed the elevators. But even more interestingly, when I lubed the elevator bellcrank - and I made a real effort to get some new lubrication tools and do it thoroughly - the bellcrank lube reduced elevator resistance even more greatly than the elevator hinge lube.

                    I suspect I wasn't effectively lubricating the bellcrank at 100hr checks, and that the resistance very gradually increased over the 3 years we've been flying.
                    Last edited by Battson; 12-14-2016, 03:30 PM.

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                    • #12
                      Why the push to move away from mini zerks? Oil holes depend on the low viscosity penetrating action of oil. Forcing some thin grease in via a real grease fitting seems to make more sense, but it seems people have moved away from that. Why?

                      I'd like to develop a new version of that hinge that uses a teflon bearing insert and allows easy servicing.
                      Last edited by Zzz; 12-14-2016, 03:51 PM.

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                      • #13
                        It's a good question. I don't know the answer.

                        If I had to guess, I would assume it's because the basic lube-hole:
                        - is the simplest design
                        - is easier to fabricate
                        - cannot fail in any way
                        - has fewest parts / light weight
                        - no added drag
                        - time-tested
                        - proven to provide sufficient lubrication

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                        • #14
                          The Christen Eagle uses a strap hinge with bronze half shells for bearing surface. The design could easily be incorporated int a scratch built BH on initial construction if a builder was inclined to do so. As far as leaving off the zerk fittings I made the decision based on the potential of over greasing the hinges and ending up with a mess in the slipstream. The eighth inch hole works fine. I never found an issue in 800 hours worth on my Pitts.

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                          • #15
                            I am probably the reason why there is a push away from great fittings. For I am capable of driving a grease fitting with .240" of threads beyond the .058" hinge material and hit the inner post of the hinge resulting in damage, and now a frozen flight control surface. If I did get it right, I would be stripping out the grease fitting on a regular basis, wondering how everyone else is having success.

                            Brooks Cone

                            Brooks Cone
                            Southeast Michigan
                            Patrol #303, Kit build

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