Trim your airplane to fly straight and level with about 60 to 75% throttle; then reduce the power to idle as it passes in front of you, or where you can see it clearly, and watch what happens.
If the plane pitches up, then you have too much downthrust.
If the plane dives or pitches down where you have to hold more than just a little back stick for glide. then you need to add downthrust
If the plane slows down and then pitches down into a gentle glide, then your thrust angle is correct.

feihu