GFC-500 altitude hunting

[khedrei]

Alright so I know there is a thread on the this but my problem seems a bit different so I thought I would start a new one.  I think Don had a problem with his and from my recollection the solution ended up being to clean and lubricate the controls.

Mine is hunting up and down 20-40 feet at a time. I attached a video of my last flight. The odd thing about this compared to Don's (which from my recollection it was basically all the time) is that mine is intermittent. In smooth air sometimes it's fine and other times it's not. The weird thing is that it seems to do better at holding altitude in light chop or even light turbulance than it does in smooth air.  Also, in the video, it is using the trim to make these oscillations. Should it not be using pitch to keep level? The video shows up and down 300 ft/min but it was occasionally up to 500. 

Though I have not ruled out dirty controls which I will check tomorrow, the intermittent nature of this seems to suggest it's something else. I asked around the airport to people that know more than me. I was told to try checking the settings which I seem to be able to access on my own in the G5 but dont want to mess with.  He thinks it sounds like it's getting bad or delayed data. Also told to check possible water in the static line.

Any other suggestions are very welcome. Aircraft was loaded 400lbs under gross with a normal c of g. 

 

 

[khedrei]

Sorry, I seem to have loaded the full quality video from my phone at 122 Mb. It's slow to load on my internet connection so I assume it will be for others as well. 

[hypertech]

Not sure about your autopilot but it looks like there's something up with your units between the main display and the G5.  If they missed the units, maybe make sure they put the gains in right?

[Pmaxwell]

Looks like the elevator controls need to be checked. If there is just a little resistance in the controls it will cause the trim Servo to kick in to relieve the tension on the elevator servo.  Most of the time this resistance is due to dirty or dry yoke shafts. Moisture in the static line is also a common reason for oscillations. I’d lube the yoke shafts and go try it. Then check for moisture. 

[carusoam]

Hey a PMax sighting! 

Always good to have the input from PMax...

Thanks for sharing, Paul.

Best regards,

-a-

[khedrei]

 

On 6/29/2020 at 10:19 PM, Pmaxwell said:

Looks like the elevator controls need to be checked. If there is just a little resistance in the controls it will cause the trim Servo to kick in to relieve the tension on the elevator servo.  Most of the time this resistance is due to dirty or dry yoke shafts. Moisture in the static line is also a common reason for oscillations. I’d lube the yoke shafts and go try it. Then check for moisture. 

I think it was a control dirtiness issue. I hadn't thought that would be the case because it had just gone in for annual and I had requested them to clean and lube and they had. But we had done a bit more work on the right side and I think it got dirty again. I cleaned everything before the next flight and it was much better. 

Thanks for the tips.