removing the bottom wing will make it a bit faster, require a little more throttle to gain altitude, and handle a little more wind. on the flip side, adding the bottom wings to the top wings will do basically the exact opposite. also, adding the bottom wings to the top may make your turning radius a bit larger too.

here's a little plane i made today with the AA's electronics. its a tandem wing design, 6" long wings, 2" chord, AUW of 12 grams. it flys amazingly slow, but very fragile, so i made another one using all 1/16" balsa. doing that gave me one more gram in weight, but i can live with that, plus i need the extra streangth when i fly at work (concrete + balsa = little balsa bits. d'oh).

nick