Canard vs. Rudder placement

[noobflyer92]

It seems lots of fighter jets utilize canards in the front of the aircraft for pitch control. How come the rudder is in the very back of the plane then? Is it visibility issues? Or the instability of putting a rudder up front? I've tried with gliders and I can put a canard up front, but when I put the rudder up front, it gets wildly unstable and slips out. Anyone know why this is?

[JetPlaneFlyer]

The rudder is at the back for the same reason that an arrow has it's vanes/fletchings/feathers at the back... Because if you put the fin/rudder at the front the plane will try to fly backward just like an arrow would fly backward if you put the vanes at the 'pointy end'.

In more technical language to be stable the aerodynamic neutral point of the plane needs to be behind the CG. This is true in terms of planform area (for pitch stability) and in side area (for directional stability).

In plan you can have a canard up front because you have a great big wing behind the CG.. The stabilising influence of the wing overrides the de-stabilising canard.

In the case of the front mounted vertical fin there is no 'wing size' vertical flying surface behind the CG.. So the model will be wildly unstable. If for some reason you wanted to add a front mounted fin then for stability you would have to add a rear mounted fin that was much larger.

Steve