JJ Sinclair wrote:
One thing I haven't seen in this discussion is the fact that the Duo's
spoilers are not located right behind the spar. They are located quite
a bit farther aft and thus produce mostly drag and not as much spoiled
lift. I liken them to the H-301 Libelle spoilers that produced mostly
dray and therefore had to be opened earlier and left out longer to get
the same result as, say the H-201 Libelle which had true spoilers
located at the high point of the airfoil.

My opinion is the opposite, Duo spoilers likely do an adequate of
spoiling lift, what they don't do is produce much drag. By comparison,
the trailing edge dive brakes on my Ventus caused an increase in lift
through much (if not all) of their travel, while they were producing a
tremendous amount of drag. I found it a lot easier to make steep short
landings in the Ventus than in the Duo...

Marc