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Does your elevator drop down by its weight?

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  • Does your elevator drop down by its weight?

    My elevators stay at whatever position I leave them. I had an A&P visit me and check out the plane and he was of the opinion that the elevators should drop down due to its weight on the ground. I measured the stick forces and these were between 1.5 - 2 lbs for both the elevators and the ailerons. Since the elevators are balanced I presume they should stay where ever they are left. Comments please?

  • #2
    This from the assembly manual :
    when the word “balance” is used, that means putting enough lead in the balance area (the part sticking ahead of the hinge line) so that, when the surface has paint and fabric on it, it will balance horizontally (push it down and it comes back up and vice versa). ”

    Mine currently stays neutral where I put them, but I’m in the build process with no paint on yet.

    I’m still getting some friction through the joystick mounting. If I tighten the bolts (those pesky difficult to access ones) it appears to be slightly deforming the bushing and adding friction.
    Last edited by Nev; 10-31-2020, 06:01 PM.
    Nev Bailey
    Christchurch, NZ
    Builders-log

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    • #3
      They should stay where you put them. Given the substantial friction in hinges and cable pulleys, it would take quite a bit of imbalance for them to do otherwise.

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      • #4
        That is my understanding as well. And a little overbalance is preferred over under balanced, if you have to err. I remember that from many years ago, but I think it was also repeated on this forum.

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        • #5
          Having set the rigging on several Bearhawk’s
          I offer the following:

          1. An individual elevator supported on the hinge line should go counterbalance down toward earth.

          2. An elevator assembled to the horizontal tail, joined together at the control cable attach arms, with the horizontal tail strut and flying wires set to flight tension.
          Elevator should drop counterbalance nose toward earth freely. If not something is miss aligned and or binding.

          3. The control stick assembly should rotate freely and free fall to the stops when released.

          4. After attachment of the elevator control cables and during tensioning, some light friction is expected.
          That said I am still able to achieve elevator counterbalance down to the stop with only a slight initial
          input from static condition.

          Much more friction than that will be difficult for stability to return to pitch airspeed and causes the autopilot and
          pitch trim to hunt.

          Pilot also smiles better. : )

          Kevin D

          # 272

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          • svyolo
            svyolo commented
            Editing a comment
            That is a great description, especially the details about have strut, flying wires, and control wires being tensioned, and making sure friction is minimized AFTER all those are accomplished.

          • gregc
            gregc commented
            Editing a comment
            Agreed, good explanation. One other note, on my kit I had to carefully clean out the hinges to achieve the condition described. I little grit or paint over-spray in the hinge is enough to cause objectionable friction. I flushed them out with a syringe and mineral spirits while working them back and forth.

          • zkelley2
            zkelley2 commented
            Editing a comment
            Greg agreed, I've found it difficult to keep them clean enough to be friction free.

            I've also found it about impossible to keep water out of the elevator hinges, which I might have a post on by itself on what problems that has presented.

        • #6
          Mine stay where I put them, unless the wind is blowing Same with the other Bearhawk / Cessna / etc aircraft with balanced elevators which I have seen.

          If they tend to drop down then they are over/under balanced. Bob's design calls for balanced, not "almost balanced". Maybe the person you were talking to didn't clearly communicate what they meant.
          Last edited by Battson; 11-01-2020, 07:28 PM.

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          • zkelley2
            zkelley2 commented
            Editing a comment
            I've never seen a Cessna not be a bit overbalanced. Front of the elevator down.

          • schu
            schu commented
            Editing a comment
            My 1949 C-170 doesn't have any counterbalance weights in the elevators, thus the elevator is down unless you are actively holding it up with the yoke.

        • #7
          Thanks for the detailed steps Kevin.

          I disconnected the elevator cables from the bell crank and started checking through the list. With everything disconnected my setup passes test 1, but am stuck on step 2.

          In step two after attaching the tail strut tightening the flying wires to flight tension, 3/8" movement with 15lbs force, the elevators become stiff and do not drop down easily.

          Since there are four places where the horizontal stabilizer is being supported, it is surely an imbalance among these four?

          I have a sure way of checking the tension on the top flying wire, but not sure how to make sure the strut and the bottom support corresponding the top flying wire can be accurately tightened.

          Wondering if it would make sense to separate the two elevators at the control cable attach arms, get the two elevators properly working independently and then join them at the control cable attach arms? This way I can at least isolate one of the four variables


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          • svyolo
            svyolo commented
            Editing a comment
            Is your fuselage covered? If not you should be able to visually see that your elevator hinge line is straight both horizontally and vertically. Vertically still shouldn't be hard to check if it is covered, but being in a horizontal straight line might take a bit more creativity.

        • #8
          You are going down the correct isolation path.
          A few pointers.

          Any miss alignment that causes a side load on the relationship between any of the hinges will bind.

          The elevators should bolt together at the control horn.
          if this results in the spacing between the hinges binding on the the sides you will need to place a shim between the two horns or a shim between the horizontal tail and the fuselage when the tail is slid on.

          Both the “Spar” tube of the horizontal tail and the elevator need to be straight, in vertical and horizontal.

          With everything as straight as possible. Secure the outer hinges first, look and see if the holes on the inboard strap hinges are in line and will accept a bolt.
          if parts are not aligned there will be binding.
          repeat by bolting in the inboard and checking the outboard alignment and friction.

          You may find that the strap hinge holes need a bit of love to align. I had one scratch built plane, nicely done, that required doubler washer welded to strap and re drilled, hole location was out 3/16 of an inch.........

          Hope this helps sort out the process.

          Kevin D

          # 272

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          • haribole
            haribole commented
            Editing a comment
            Awesome! Thank you! Thank you! Thank you!

        • #9
          Great description On how to get smooth elevator action Kevin!

          Like Battson, I followed the plans and weighted the elevators so they stay where put. A bump gets them moving and they coast for second then stop. Mine might be a smidge under-balanced, I can’t remember for sure, but I wanted keep the tail as light as possible for CG reasons. With that long of an arm ounces matter.

          I use grease in my hinge points. I currently just use a disposable chainsaw nose sprocket grease gun. I’ve thought about getting a refillable grease gun and using the same grease I use on my boat trailer wheels bearings but so far I haven’t seen a need.

          What is the reasoning for overbalancing the elevator?
          Scratch Built 4-place Bearhawk. Continental IO-360, 88” C203 McCauley prop.

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          • #10
            I added small grease fittings to my hinges as any grit will cause binding. I emphasis the comments about alignment. I built a long straightedge today makes sure the elevators are in a perfect line with tail wires brought up to tension. There is not much margin for error in the tail alignment otherwise the elevator will bind.
            Last edited by spinningwrench; 11-03-2020, 07:56 PM.

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            • #11
              There are some great threads in the archives. Sometimes they are in threads titled something different. Jared does rename or move stuff occasionally. I think this one might be a good one to make easier to search for.

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              • #12
                Originally posted by haribole View Post
                My elevators stay at whatever position I leave them. I had an A&P visit me and check out the plane and he was of the opinion that the elevators should drop down due to its weight on the ground. I measured the stick forces and these were between 1.5 - 2 lbs for both the elevators and the ailerons. Since the elevators are balanced I presume they should stay where ever they are left. Comments please?
                Get a new A&P. He doesn't know what balance is.

                Comment

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