Coaxial helicopter CG Point

Hi, I am making a coaxial helicopter and I am testing the drone.
I crashed during the flight test this time and there are some issues.

The first issue is the center of gravity of the helicopter.
I took two flight tests as shown in the log below. In the second flight test, I removed the battery (1.2kg) for a lack of thrust.

In the second flight test, the aircraft took off and crashed.
Looking at the log file was not a vibrating divergence. It was a divergence with a slow frequency.

I simply can’t figure out if it’s a fall due to center of gravity or if gain tuning is less.

1st Flight Test

2st Flight Test

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Hi there, I hope you’re still checking this forum every now and then. I would be really interested to know if you managed to figure out what the problem was? What made your helicopter crash? What caused that low frequency divergence? Thank you very much in advance.

We are doing same project in Turkey. If you are interested please send me and email.
My email is