HI NEED SOME thoughts on the use of engine down and right thrust to improve a planes flight characteristics down thrust of 2-3 degrees i think will help the plane fly inverted a bit more easily right thrust is used to offset engine thrust please only respond if you have years of building, flying and trimming airframe experience
i have been building and trimming for 20 years-i have always set my stab-wing and engine at zero degrees to each other i was told by the best 3D flyer i ever knew-that an airframes balance is best judged with the plane inverted-you s/b holding just a bit of down elevator for the plane to be flying level i think some down thrust allows you to have a more tail heavy airframe so you can fly 3D-let me know what your experienced thoughts are on this subject thanks in advance ENJOY REGARDS TONY

Is your thrust line in line with the wing and stab CL? If so, down thrust probably isn't needed. If these lines differ, then it might be good to have some.

2 or 3 deg of right thrust is standard on most planes I like to fly (3D profile, pattern) and I trim the CG just as you describe.

After doing that, I like to use down thrust ONLY if I believe uplines are being skewed by thrust. To test that I first climb at various speeds and observe canopy or belly pulling and then compare with power off dive tests. The dive test should give perfectly neutral but climb test may differ and that would dictate how much down thrust. Some like to trim down thrust for level flight at a given speed, but I like to look at the uplines because they are easier to see (plane far away, line is always vertical, vs coming and going it's hard to judge perfectly horizontal unless you're VERY low).

Then I fly KE and see how it behaves. Normally, I just like to mix out any coupling there with the rudder/elev mix.

Check up/downthrust in a level/trimmed powered flyby. Cut throttle. Obeserve up or down pitch. Ideally it should continue level for a ways.
Back to full power. It should not pitch up or down, but continue a level flightpath. Adjust engine thrust to achieve a neutral behaviour.

Side thrust is checked with a level powered flyby, then smoothly pull into a vertical. If you need execessive rudder to draw a vertical line, adjust thrust line L or R

Your flying surfaces must meet required incidences per manual before the above is tested with success.

He posted this in the 3D forum, so that's why I biased my answer away from your more pattern oriented suggestion. I'm assuming he's near perfect neutral on the CG and elevator trim. If that's the case the plane should really drop equally inverted AND upright when chopping the throttle.

In my suggestion, observing up and down lines takes the gravity and CG variables out of the equation because if downline is truly vertical, he's got that right. All that remains is the downthrust variable and the engine angle is the largest factor while climbing once the others are set. Of course, he needs to view these from the side to observe pitch changes. Maybe I didn't make that clear.

I like your method for true pattern and park flyers, but even so the "trimmed for level flight" method assumes a certain speed if the CG, decalage and airfoils aren't optimum for aerobatics.

The 2 or 3 deg right thrust seems to be a good starting point. I like to check that when hovering to see if I keep needing to correct for right or left rudder. Again, a 3D answer vs your pattern oriented suggestion.

Many ways to skin a cat, I'm sure.