I am not trying to be the bad guy here but..........Both of the planes pictured had two blade props fitted to them. This effectively doubled the air speed of this plane.This wing design may not be the best.
However Horizon may baulk at the prop change. I have flown a few of these and the three blade prop along with the needle valve limiters are a pain. At least for an experienced flyer. These things did however keep the air speed way down. Please don't take this as criticism. I would have done the same thing with the prop. I just think you gave Horizon a way out of their liability.

David