<<Apparently, the downward exhaust column provides significant drag.>>

Jim Ayers of our local EAA chapter did a bit of work on is LOM-powered RV.
His conclusion was that the exhaust plume is just as solid an obstruction to
air flow as a metal deflector.  Thus, when the pipe is directing the exhaust
away from the aircraft you have to assume the frontal area increased not by
just the pipe, but by the plume that extends for some distance away from it.
Another comment on the deflected exhaust pipe is that the length of the bend
is not sufficient to significantly change the direction of flow, but will
cause significant turbulence right at the outlet - which might explain the
exhaust stains on the outside of the pipe.

Gary Casey
ES project