Motor size
 

I have this airplane it says 20cc but I don't know if it is to small some opinion

http://www.phoenixmodel.com/phoenixm...?ProductId=290

Not sure if you wonder if the engine is too small or the plane is too small for the 1.20 engine? The plane is slightly smaller then my CG Extra and I fly it with a 1.20 YS four stroke and have even used the OS 1.20fs. Today you can even use the 20cc gas engines in it.
If you go into the ARF forum you will probably find the plane there and see what others are using and what they think of there combos.

A friend of mine has the Hanger 9 version, it's slightly smaller at 62" span but it flies great on a Saito 1.20. If you want scale performance its more than enough... if you want to pull the wings off it then go bigger. :D

Also not sure what you are asking . You say motor then say 20cc. Are you going electric or gasoline? Specs state its a 120 size plane .
If electric then a Power 110 would fly it , if gasoline a 20cc would fly it. For me ,I would put in a 26cc gas .

20cc gas is plenty of power or in a 2stroke .75