Samalot, The size compairison of a .46 sized monoplane to a .46 sized biplane does not necessarily mean the biplane will be heavier, and that is what you have stated. There are many aerodynamic factors involved here. However, in simple terms; aerodynamically, biplanes suffer from more drag due to interaction between multiple wings and the increase in induced drag from them! This is why they need larger engines for a given aircraft size and why they need to exchange altitude for airspeed, when the engine quits!