MidContinent CDI vibrating needle issue

Discussion in 'Avionics and Upgrades' started by DesertNomad, Dec 19, 2018.

  1. DesertNomad

    DesertNomad Pattern Altitude

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    I picked up my plane with new G5s today.

    Previously I had a 750 hooked to a MD200-706 and a GNC255 hooked to a GI-106A. I removed the GI-106A and connected the MD200-706 to the CGN255 because the 750 is now connected to the G5.

    I am either seeing a weird parallax issue, reflection or my MD200-706 needle is vibrating at a high frequency fore and aft. The needle is clear when it is centered, but if I look at it from off-center it gets blurry. It did this with two different VORs.

    A video is here:

    http://www.xericdesign.com/archive/CDI-Video.mp4

    Is this supposed to be like this? I have had this instrument for just over a year and don't recall it being like this. I got it at last annual in late October 2017. When I dropped off my plane at my shop in late September 2018, it was not like this (at least I don't think so). I just picked it up today and flew it from Portland to Reno.

    Naturally, it is 6 weeks out of warranty now... except it has been in the shop since before the warranty expired.

    Thoughts?
     
  2. bnt83

    bnt83 Final Approach PoA Supporter

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    Does it change with engine RPM?
     
  3. DesertNomad

    DesertNomad Pattern Altitude

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    That's something I need to check. I plan to test it on the ground today without the engine running. I normally fly at 2300rpm and have never seen this before. It was doing it at cruise.
     
  4. bnt83

    bnt83 Final Approach PoA Supporter

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    My guess would be that the G5 installation significantly changed the instrument panel's harmonics. Maybe jut changing how the wires are tied up would stop it.
     
  5. DesertNomad

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    Works fine n the ground with the engine off. I'll fly it in a couple days.
     
  6. Unit74

    Unit74 Ejection Handle Pulled

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    So dead on, its good but from the side angle, vibrating. So the needle is vibrating fore and aft, not side to side the way I see it. Call MICO and ask them if they have ever seen this. Looks like a disaster waiting to happen.
     
  7. DesertNomad

    DesertNomad Pattern Altitude

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    Yup - fore and aft. They have never seen this issue but I am in touch with someone there to run some tests since they know the instrument better than anyone.
     
  8. DesertNomad

    DesertNomad Pattern Altitude

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    Yes.

    I flew it today and found that it starts vibrating at about 2280rpm, peaks at 2330 and stops at 2350. Since I normally fly at 2300, it is a bit of an issue. I have asked my shop and MidContinent about it.
     
    Last edited: Jan 12, 2019
  9. Unit74

    Unit74 Ejection Handle Pulled

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    Any answers yet?
     
  10. DesertNomad

    DesertNomad Pattern Altitude

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    Swapped the instrument - no change.

    Re-balanced the prop (down to 0.04 on the meter) and the problem range moved from 2260-2360rpm to 2220-2320rpm.

    Today we’re trying the old GI106A.
     
  11. bnt83

    bnt83 Final Approach PoA Supporter

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    I'd probably put a shim between the instrument and the panel and retest
     
  12. Doug Reid

    Doug Reid Pre-takeoff checklist

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    Try putting your finger on the panel in different spots around your instrument to see if that reduces the vibration any at all. I used to me a recording engineer before I became an A&P. Changing the mass of the panel will change the resonant frequency of the vibrations, if that is the source of your problems.

    This might work...isolate the unit from the panel, or add a damper ( foam ) between the instruments .

    Good luck............
     
  13. DesertNomad

    DesertNomad Pattern Altitude

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    I have tried touching the panel in different places with no change. The GI6A also vibrates but in more of an up/down and not as severe.
     
  14. DesertNomad

    DesertNomad Pattern Altitude

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    Progress as it is stable out of the panel so it seems the old vacuum gyros aided in dampening it. A&P working on a solution. There are sunken holes to screw the instrument in so not sure about a shim or rubber gasket since the vibration would be transferred through the screws.

    Maybe the vacuum hoses used to provide a damper connecting the firewall to the gyros??
     
    Last edited: Mar 15, 2019
  15. Unit74

    Unit74 Ejection Handle Pulled

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    Screw it./.... Buy a G5 HSI.
     
  16. DesertNomad

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    I already have dual G5’s. This is for nav #2
     
  17. Unit74

    Unit74 Ejection Handle Pulled

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    OOOOOhhhh.... A triple G5 in the works! Sometimes ya jes gotta let it go. Ya know..? Accept change. I dare ya to put in another G5.