The Custer Channelwing is controversial. I think the channelwing is a form of deflected prop thrust. Nick told me once that deflected thrust is not as good as direct vertical lift. I think he is probably right. Some people think the channelwing works.
I watched an experimenter flying a single engine channelwing of his own design. It was a pusher with a channelwing behind the cockpit. The problem, as I saw it, he could not descend for landing without reducing power and so he had no lift gain while landing. Might have helped for takeoff but I did not see any better performance, maybe worse than a stock Cub.
slowrotor