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Touring Motor Gliders Association (TMGA)
Eric Greenwell

Dynon CHT needle flutters

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Eric Greenwell

During my 2/6/2019 flight, I noticed the left CHT needle on the Dynon was fluttering between 130-145, while the right CHT needle was steady. That was with the cowl flap fully open; with the cowl flap fully closed, both needles were steady. I've never seen the fluttering before.

On the ground, I did not see any problem or change in the sensor or the connector to it and or it's wire. Wiggling the wire next to the connector did not cause the needle to wiggle. Note that the Left CHT is on the upper left, front corner of the engine; the Right CHT is on the upper right, rear corner. The left air inlet on the cowl blows air almost directly in the upper left, front CHT (the right/rear sensor shielded from the right cowl inlet), so it's hard for me to imagine how the airflow from the cowl scoop could affect it.

Any ideas?

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edwalker

Hi Eric,

I’m not sure if this is related or not, but I had problems with the same connection. My EGT was wavering in flight and when I checked it the left front sensor wire was almost imperceptibly  loose. The clamp was tightly adherent to the exhaust pipe but the wire could be moved, and I could feel the sensor shake ever so slightly inside the ceramic insulator. This happened right before one of my annuals, and Jim Scott put some RTG on the connection to stabilize the wire within the ceramic insulator. no problems since.

 I’m not sure that this applies to your situation,  but it may be worth taking the sensor off the exhaust pipe and looking at the integrity of the probe from the other side to check for motion. It will also let you check the sensor ground. Might be good to put a VOM across the sensor and wiggle the wire to see if there is any variable resistance and compare it with the other sensor. It may be that this part of the engine is subject to stresses that are different  than the opposite EGT probe, and there may need to be some additional wire tie support for the lead going to the probe.

Ed

 

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Eric Greenwell

In my case, it's the CHT (not the EGT) that's wavering, but your comments give me couple ideas: I'll check the wire connection to the sensor clip more carefully, and I'll exchange the right and left CHT sensors to see if the problem moves. Right now, we have 8" of snow on the ground, blowing snow in the air, and a ceiling of 1400', so it'll likely be week before I can test it  ☹️

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