The Mirage is already a well-designed electric airplane; its design clearly takes advantage of lightweight building techniques with little sacrifice in strength (in fact, the wing is often regarded as ``overbuilt''; but for a trainer this is not a serious vice!). Thorough sanding of all parts and adding lightening holes where possible (see the stab and fin figures below) can remove unnecessary balsa and boost performance.
To improve the aerobatic capabilities of this plane, the dihedral was reduced to slightly less than half its normal value (this was accomplished by sanding the dihedral joiners to the appropriate angle) and ailerons are added for 4-channel control. Ailerons can be built-up from 1/16'' x 1 1/2'' x 36'' sheeting for a stiff and lightweight solution. I chose an easier solution, however - namely stock aileron strips cored with lightening holes. The weight difference isn't significant, although they aren't as stiff as built-up ailerons. Unlike the figures, I use 1'' strips of Monokote spaced every 2-3'' for all hinges. They're very lightweight and strong - but most importantly they provide a gapless hinge for minimal flutter risk and maximal control authority. For .40 sized planes and smaller, they're definitely worth considering.
Adding ailerons to the structure is fairly straightforward. All ribs were cut short to accept the 1 1/2'' ailerons and the 3/8'' x 1/4'' trailing edge. Notches are cut into the trailing edge so that the ribs fit and hold without CA. The ailerons may seem large for a .20-size model, but due to the slow, scale-like flying speed of the Mirage, large ailerons are necessary for authoritative control.