Elevator/Pitch Trim Stickiness

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jbrauertn
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Elevator/Pitch Trim Stickiness

Post by jbrauertn »

I have a DA62 which is serial number C.005, one of the first out of the London, Ontario plant. I have loved the plane for bit over a year now. One of the ongoing issues that I haven't yet seen discussed on this forum is regarding stickiness in the pitch trim. I know the procedure I've been taught in order to prevent it most of the time, but want to eliminate it completely!

My DA62, and I assume all of the others, has a small (approximately 1/4" x 6") long polished stainless steel shaft that slides through a small plastic (UHMW) block located in the opening at the center rear of the elevator adjacent to the trim tab. The shaft is connected to the trim elevator tab and apparently adds friction to the system. It is adjusted during installation on the aircraft to a predefined friction level and cannot be adjusted from the cockpit by the pilot. I'm sure most of you know the device I'm describing. If not I can take a picture of it and add it to the post for better definition. Let me know if a picture would help.

Anyway, when the plane was delivered I was told that this device needs to be cleaned with isopropyl alcohol on a regular basis as it will begin to stick if it gets dirty. The stickiness can be felt as a "tight spot" or "notchiness" in the manual pitch trim wheel in the cockpit. If the stickiness gets too much it will cause a fault in the electric pitch trim which is displayed on the PFD and subsequently prevents the autopilot from arming and working for the duration of the flight.

I religiously clean the "friction rod" per instruction as a part of my regular preflight and have prevented the issue in all but a few cases.
However, it seems that the problem is much more prevalent when the anti-icing TKS is used. It appears that the TKS fluid gets into the opening in the tail and subsequently contaminates the friction device. While Diamond says the fluid will not get onto the device, my eyes and a clean cloth prove otherwise. With the cold weather fast approaching I thought I would ask the group if anyone has found a "long" term solution to this ongoing pain in the butt.

I've taken my concern and questions to my Diamond trained A&P and to Diamond directly with no response indicating any consideration, potential modification, or possible correction of the system in the works.

Perhaps I'm doing something wrong or perhaps others are experiencing issues similar to me. Either way I'm open to any and all suggestions.

Thanks all!
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Steve
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Re: Elevator/Pitch Trim Stickiness

Post by Steve »

The DA40 has the same pitch trim damper. It is there to prevent trim tab flutter should the pitch trim cable fail. In addition to cleaning, you should ensure that the tension on the rod is set properly:

viewtopic.php?f=8&t=3489&p=68596&hilit= ... rim#p68596

Steve
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neptune2528
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Re: Elevator/Pitch Trim Stickiness

Post by neptune2528 »

Jeff - thank you very much for the post. I recently took delivery of C015 and have definitely noticed a stickiness as well. However, no mention of the friction device and need to frequently clean the rod was made at the factory on delivery. Could I trouble you to request you post a picture or two of what needs to be cleaned? This definitely sounds like a procedure I need to be doing on C015.

Thanks!

Jason
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Re: Elevator/Pitch Trim Stickiness

Post by CFIDave »

There should be no need to frequently clean the rod in the tail, regardless of whether it's a DA40, DA42, or DA62 -- they all have the same basic mechanism. I've only cleaned the rod on my DA62 once or twice in 350 hours of flying it, using only a clean dry cloth rag (and it really didn't need it; there was no dirt or residue that came off). The rod definitely should not have to be cleaned as part of regular pre-flight checks.

What's more important is having the friction damper tension on the rod adjusted properly -- or far less commonly adjusting the tension on the trim handwheel mechanism inside the cockpit (e.g., on one particular DA40 the GFC700 autopilot couldn't hold pitch in level cruise at higher airspeeds -- the wheel kept slipping).

If the handwheel is sticking, check the tension/force needed to move the damper rod thru the clamp with something like a spring (fishing) scale, and adjust the tension (per description in the AMM).
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Rich
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Re: Elevator/Pitch Trim Stickiness

Post by Rich »

Mine will develop a "stickiness" from time to time. Maybe once a month I check/clear it by running the trim wheel to the forward and back stop a few times.
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Tim H
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Re: Elevator/Pitch Trim Stickiness

Post by Tim H »

Likewise, I run the trim wheel full travel (by hand) as part of my pre-flight for two reasons, 1) to make sure I have full travel and 2) to help eliminate sticking. At my annual, I remind the the A&P not to lubricate the nylon block as this just attracts dirt.
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Re: Elevator/Pitch Trim Stickiness

Post by jbrauertn »

neptune2528 wrote: Tue Nov 19, 2019 8:08 pm Jeff - thank you very much for the post. I recently took delivery of C015 and have definitely noticed a stickiness as well. However, no mention of the friction device and need to frequently clean the rod was made at the factory on delivery. Could I trouble you to request you post a picture or two of what needs to be cleaned? This definitely sounds like a procedure I need to be doing on C015.

Thanks!

Jason
I'll get a picture in the net week or so and post it here.
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jbrauertn
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Re: Elevator/Pitch Trim Stickiness

Post by jbrauertn »

Thanks for the comments. Maybe I'm overly sensitive to the stickiness.

To address a few items brought up in the comments:
  • The delivery pilot/CFI specifically showed and explained the need to clean the damper with alcohol on a regular basis.
    The damper has been removed and adjusted per the factory specs.
    I also never see any dirt, except TKS fluid, when I clean it but the stickiness still becomes apparent at times.
    I also run the trim from stop to stop prior to each flight.
One thing I haven't done is to try different adjustments on the trim wheel tension inside the cockpit. I will certainly test that in multiple settings to see if it alleviates the issue.

Thanks!!
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Rich
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Re: Elevator/Pitch Trim Stickiness

Post by Rich »

One other thing is that I found a bolt in the trim wheel hanging up on a piece of excess upholstery beneath the copilot seat. Xacto knife cured that.
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Re: Elevator/Pitch Trim Stickiness

Post by Colin »

I had this trouble in my DA40 more than my DA42. I used to run the trim (by hand) stop to stop three times. Every three weeks, I imagine.
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