InFLight Tuning diagnostics

[cbretana]

I ma experiencing pitch oscillations, i.e., the Altitude hold is not stable, Altitude oscillates up and down around the target altitude with magnitude of between 30 feet to 180 feet, with a period of about 35-45 seconds. In the Inflight Tuning process guide, the only thing I can find that seems to be a matchfor this is the diamond labeled "Does aircraft over and undershoot target, gradually getting closer" in the flowchart in Figure 5 on page 5-4. But in my case it does not "gradually get closer". In my case the oscillations start from a level fligh tcondition, and gradually get worse. Should I try to increase the VSI gain for this? Or is there another place in the document that I should be looking?
Also, what exactly does the document mean by "Twitchy"

 

[RVDan]

I think that generally “twitchy” means, short term oscillations without the aircraft actually deviating much from the selected altitude. Imaging moving the stick in fast short motions without climbing or descending. Essentially, the AP is overreacting to small changes.

As for your altitude hold deviations, I would go back to the beginning for pitch tuning and start from there. I would recommend recording your current settings so that you can get back there if necessary. It takes a little time to get this correct, and can take some fussing to get each step good.
I have an RV-6 and if I get altitude hold just right in smooth air ( not twitchy), it lets altitude deviate a bit in rough air conditions. Still way better then hand flying though.
When I worked in the development of big airplane AP systems, there were perhaps a hundred variables or more getting tweaked to get it to fly perfectly in all conditions. Of course the cost of the AP development was several orders of magnitude greater than the Dynon AP .

 

[cbretana]

Thanks! I have a Long EZ and this oscillation behavior does not always happen. But when it does it does happen it does not die out, it just gets worse. I find that the only way to stop it is momentarily disconnect AP as it is just about to pass through target altitude, (into CWS mode), hand fly it to stop the vertical velocity on or near target, and then release CWS to turn on AP again.