So let's take this same S.E.5a and change the angles.  Set the engine to -5 degrees, wing to 0, stab to -1.  Should fly the same, right?  Except the fuselage will move through the air at a different angle.  <div>
</div><div>Anyone looking at the plane after changing the angles would immediately say it has downthrust, even though all the relative angles are exactly the same as they are in the picture above.  Of course, in the picture above, the plane doesn't look like it has downthrust to most people.</div><div>
</div><div>Now here's the take home message:  A scale modeler who is using a lot of down trim to keep his plane from climbing too much might be tempted, or advised, to reduce the wing incidence.  But if he did that, he would reduce the downthrust, unless he changed that too.  You could build an S.E.5a with 0 wing incidence, but then it wouldn't have any downthrust.  Even worse, it wouldn't look like an S.E.5a anymore.  Wing incidence is a very noticeable characteristic.  Why bother building a scale model if you're going to undo the effect by changing the wing incidence?</div><div>
</div><div>With reduced wing incidence the plane would indeed use less down trim, but that's not the real problem.  Who cares if you are carrying down trim?  The real problem is the difference between trim at low throttle and high throttle.  </div><div>
</div><div>Of course full scale airplanes have this "problem" too.  That's why pilots are taught that the throttle, not the elevator, is to control climb and descent.  But many people expect their scale models to fly like their sport models.  That's the real source of the problem.</div>