I have a 40 size trainer that flew well with a borrowed Duraplane 40 wing. I built a new wing which is 8" longer spanwise and 1" longer chordwise.

Problem is, the plane wants to either climb slightly or decend slightly. Seems there is no way to trim it to fly straight. This happens at most power settings

Do I have the CG wrong? What about the increase in chord length?

Ok a couple of things to check

Check the CG, say the old wing was 9" wide and the new wing is 10" wide you will need to move the cg back about 1/4" or the other way if the new wing is narower so move the Cg about 1/4" per 1" of diferance.

also check the ailerons are not dropping compared to the thrust line, eye ball the plane in profile and see if they are drooping compared to say underside tof the wing or the horizontal stab.

also you now have more "lift" i have an old timer with huge wing area (for weight) that just wont trim out at diferant power settings, it either climbs or dives depending on RPM i'm pretty sure it needs more down thrust but i've just got used to it.

also try shiming the wing, shim the TE first say 1/16 and see how it flies, if it's worse try take the shim out and put it in the LE.

also check your wings for too much wash out or wash in (twist at the wing tips)

good luck

Thanks! I'll try the shiming next flight.