How do I calculate the tail size of my rc plane? I'm in the conceptual design phase and my plane is supposed to be of 1.7kg. Wing dimensions are 1m*0.3m and AoA that it will fly at will give a pitch down moment of 0.03. The moment arm between CG and tail is 1m. How do i calculate the size of the tail. It's supposed to be a conventional tail.
There's a formula for calculating minimum tail volume coefficient (tail area X distance from the wing) for light aircraft.  Not sure if the same value applies to RC but it's a good starting point. This is from David B Thurston's book Design for Flying (Thurston was an engineer on numerous Grumman programs going back to the Hellcat).

(Tail Arm ÷ main wing MAC) X (Tail surface area ÷ wing area) = .55 or greater

Tail Arm is the distance from the C of G to the 30% chord point of the horizontal tail.

.55 minimum is for a symmetrical airfoil section tail typical of light planes like Cessna 150s.  I would use a higher number for a flat sheet tail surface, and being RC, so maybe .6 to .8.

While you're at it, Google "tail volume RC aircraft" and you'll find some more information specific to RC that'll be helpful.