ORIGINAL: jester_s1
On the topic of down thrust, we do that mainly to reduce speed sensitivity, most noticeably when making sudden speed changes. If there were no thrust angle, the nose on a high wing plane would rise when you gun the throttle and drop when you cut it, assuming the plane was trimmed straight at mid-throttle. Yes, the wing and engine are fighting each other at full throttle, but that little bit of efficiency is a small price to pay for a well-mannered airplane.
Full scale planes do this, and the way they fix it is with trim and training. Trim for the airspeed you want throttle for the altitude. If you gun or chop the throttle, learn to compensate until you can re-trim. I adjust elevator trim for the different phases of flight with my models. Trim for takeoff, cruise, and landing.