RE: adding flaps to an arf
Putting flaps on that would use the same process as laid out here, just with more fixturing up front. You have a very thin TE and strip ailerons so you will need to increase the width (LE to TE of the control surface). So first you need to calculate the amount of aileron you have on one panel (length times width). Take 70% of that number (for the new ailerons, you can go to 100% of the strip area but that will give a really snappy aileron) and draw the ailerons and flaps on the wing with a felt tip marker. When you have it drawn so that you like it then draw the U channel TE in place. You will need at least ½ inch sheeting to support the added stress. This will tell you where you have to put the ¼ in square balsa crutch. The crutch is CA’ed to the top and bottom of the wing to keep everything the same while you work on the wing. You obviously want it out of your way when working so it has to be at lease ¼ in away from the sheeting. I don’t think it will leave a lot of the original covering. But from that point on you will have to make new ailerons, flaps, servo mounts for each and the new TE.
Joe