What two forces? It's simply physics:
For every action, there is an equal and opposite REACTION.
SO, since you have the fan blades pushing on the air (for a propeller), the air goes BACKWARDS and the plane goes FORWARDS.
However, in your little setup, the air is contained in a system connected TO the aeroplane, thus the action of the air going BACKWARDS is negated. It's like the idea of using a giant fan to power a sailboat - the force of the fan blowing the air into the sail would negate the force of the sail catching the air. If anything, due to inefficiency and other such losses, it would have the opposite of the desired effect.
Not to mention the fact that bolting on those blocky things would make a plane so non aerodynamic as to be incapable of flight!