These pics are a bit clearer. Note the 1 degree exactly of upthrust in the model with side torque roll pick.

Entering the world of vertically trimming a aerobatic model, so you go up very high idle it, dive strait down and swap directions 180 degrees a few times on the way down to see if it drops strait down (means no trimmed lift in airframe without thrust and cg mucking up trim) then you pull strait up and put the motor in position where it goes strait up. Somewhere usually between 0 degrees and 1 degree up to wing and stab incidence which are hopefully 0 degrees to each other. on the flats the model if cg is in right spot does drop slightly towards nose but equally from inverted to upright hence slight back stick is required for level flight (which is good cause you get to choose when you want lift which is none in verticles and which way you want it upside down or upright equally). In more advanced schedules where you spend most of time flying vertically and upside down, its silly to trim only for the small percentage of upright horizontal flight.

It is possible to have the cg far back enough to be like an autopilot for you by tipping the angle of attack of the whole model so it flys on its own with no back stick. It also works the same inverted as for upright. In the verticles it doesn't affect anything lateral in the trim for cg as we know it doesn't exist in verticle flight. But the bad trade of is the moments feel short in pitch and yaw so plane feels snakey.


Best thing about trimming with zero lift in airframe it usually needs to be only set once if its correctly done. You can fly with down trust but you need lift in airframe to counter it. This ratio can change with different airspeeds and air dencitys hence the requirement to re-trim all the time to reset the balance. Also with lift in the airframe you need other fixes due to the loaded circumstance like positive differential. Please note this is for a centerhinged aileron not a top hinged aileron which will need negative differential even if zero trimmed..


Down thrust thoughts are for your high wing model like ur trainer when the wing drag and weight is above the motor (also trainers have lifting semi-symmetrical wings with angle of attack that need downthrust to stop loading up the stab with down elevator). I have down thrust in my hooning classic trainer for sure. Most of us begun our modelling experience with a trainer that does need down thrust but its funny how many forget to ween of this thought when going to low or mid models with symmetrical wings n stabs that are set up 0 incidence.

TD