ORIGINAL: TCrafty
....What I'm wondering is, if I do install the extra down thrust, could i trim out the plane so that the tail would ride lower (sag) and at that attitude, would the plane still be pulled somewhat straight (due to the down thrust)? Which in turn, would give it more lift on the wing since it's not cutting straight through the air but has more incidence to it, in relation to the direction of travel. It may be obvious that I know enough to be dangerous but I think about things like that.
ANY info is greatly appreciated.
It doesn't work that way. The model needs to "ride" at the angle that provides the wing with the angle of attack to the airflow so that it generates just enough lift to hold the model up. This is why when you're flying fast the model seems to be flying tail high (and is where the phrase "high tailing out of here" came from). And when flying slow the tail is low and nose high because it requires more angle of attack at lower airspeeds to generate the lift needed. You can't alter these angles with more or less downthrust.
Getting back to your model flying well with less downthrust..... The need for downthrust is linked partly to the location of the wing and thus the center of drag of the model. And partly it is related to the CG location and the resulting trim angles between the wing and stabilizer. The more rearward the CG is located the less the trim angle (often called decalage) is between these two and the less tendency there is to nose up with a gain in flying speed. The downthrust is there to help counter the tendency to nose up with a more forward CG and the extra decalage needed to fly level with a forward CG.