@mayan I watched the above video.
Unfortunately, it seems you were only able to capture 50% of the actual flying. Very often times you were out of frame, and it was difficult to observe the airplane. Maybe you can rig something with a hat cam for next time?
On to what I observed. In general, I think you are on the right track with the thrust angle. The first flight, looping without elevator input, is an obvious sign that the thrust angle is off. As you said in the video, it is a similar behavior to what you had with the simple soarer. After you changed the thrust angle, I feel like it flew noticeably better in regards to pitch response to throttle input.
Here is where I run in to issues with your troubleshooting methods. You are changing too many things at once and it makes it hard to see clear cause and effect relationships. By changing the thrust angle AND removing the cowling, you were making two changes simultaneously that kind of cancelled each other out. Granted, the cowl doesn't weigh much, but it is weight in front of the CG, and by removing it, you made the plane more tail heavy. So you'd have down thrust helping to keep the nose down, but less nose weight, pushing the nose up. See what I'm getting at? The down thrust would help with the pitch on power issue, but in general your plane will still be pitch sensitive due to balance being off. Additionally, after changing the thrust angle, make sure you reset your elevator trim to neutral. If you fly it with the old trim setting, it will give you a misleading indication of what the result of your change is.
On your second to last flight, you changed yet another parameter by having a different battery installed. I wasn't able to pick up if you changed the thrust angle again for that flight, but the battery came loose and the results from that flight are essentially invalid.
Based on very limited observation, I would say that your plane is suffering from three issues:
1. Your established C of G is incorrect. It needs to be moved forward to eliminate tail heaviness. You removed the cowl and the landing gear, both items that help move the balance point forward. I would add those back on to get the plane to balance better.
2. Your stock thrust angle is too high. Your second attempt had much better response to throttle (some pitch up under power for a high wing model is normal) I would leave it at "one washer down" like you had, and try to correct the CG before adjusting it more.
3. There is something wrong with the motor or prop installation. You are getting some nasty vibration above what sounds like 50% throttle. Make sure that when you put the washer on for down thrust, the motor is still securely attached to the firewall. You may need to use more or different washers to set this correct angle, but a motor that vibrates like that is not ok. It will drastically impact handling. Also check that the prop has no broken blades and that its centered on the prop adapter.
I know you're frustrated, but I think you are very close to having a nice flying airplane. Thrust angle down a bit, and move that CG forward.
And tape your phone to your forehead or something so I can actually see you fly.
