Tigerdude,
I know it seems like it should work, but like was said above, but if you remove the top wing the bottom wing usually doesn't produce enough lift to keep the plane airborne. Take for example the Sig Hog Bipe and the Sig Astro Hog. At first glance it looks like the Astro Hog is a Hog Bipe without the top wing. Yes it is true that the fuselage is the same and the two planes have the same airfoil, but they are not the same. The Hog Bipe has a bottom wingspan of 51" while the Astro Hog has a wingspan of 71". In order to compensate for the loss in lift from removing the top wing you need to increase the size of the wing left in order to produce enough lift to fly the airplane.

Hope this helps

Ken