From the looks of all the posts I've seen in various forums it seems that either pos or negative on the top wing will work, just so long as they're different than the top.

From my experience, this has got to be true because with both at 0, the darn things will never fly straight and level for more and a few seconds.

The stab seems to be a critical issue. With non-aerobatic style bipes, it seems the consensus is a couple of degrees positive will work the best.

Aerobatics seem to be set at 0 for everything with some right thrust for the engines.