ORIGINAL: rc bugman
Thanks for the replies. Somehow the responses are not logical. Here is why.
With conventional aircraft (wing in front, elevator in rear), a tail-heavy airplane puts too much authority on the elevator which makes the elevator too sensitive and the plane becomes difficult to impossible to control. Move the weight forward, the elevator loses sensitivity and the plane becomes better ''behaved''. Move the weight too far forward, and the elevator becomes insensitive and the plane becomes difficult to fly.
With a canard, the plane is backward with the wing in the rear and the elevator in front. Logic would suggest that too much nose weight would make a canard difficult to control like a tail heavy conventional plane. Elevator would have too much authority. Move the weight back and the fore mounted elevator would lose authority.
A tandem-wing biplane is yet another beast. Two equal sized wings located on either end of a fuse seems to be naturally stable where ever the CG is located between the wings.
Elson
You have to suspect that it is your logic that is flawed when your logic leads you to reason that, on a canard, "nose heavy=tail heavy." You are making an incorrect inference that the effect of moving the weight toward the elevator of a conventional design is going to apply to all configurations. The correct relation between C.G. and elevator sensitivity has to do with the C.G.s position relative to the aerodynamic center of an aircraft not the elevator.
I think part of what is confusing your logic is the names that we give to various control surfaces. Control surface names have no bearing on aerodynamic stability. We just call these different control surfaces different names out of convention more than anything else. For example, flaps on a conventional design can have the same function as the elevator on a canard: flaps go down-nose pitches up: elevator goes down on a canard-nose pitches up. You could even fly a conventional design with just flaps for pitch control without any movable elevator on the horizontal stab at all. It's the same with a canard configuration, no movable elevator on the horizontal stab. is needed. Pitch control can be had with elevons on the larger, aft wing only. We just tend to put pitch control surfaces on the wings furthest away from the C.G. for leverage reasons.