RE: adding flaps to an arf
I would look at connecting the servo to the center flap to avoid any excessive binding forces. I would have planed out how to tie the three flap together. I’ve thought about doing this many times since I lost my Zeroli, but the retracts available for this size model are poor at best so I just watch for now. I’ve been considering if building a nyrod into the center flap and then drilling a hole in the ones it mates up with for the nyrod to go through and hardening the hole with CA would do the trick. It fits KISS real well, my main concern is the flexibility may be too much.
Also there is not a lot of room there for a servo so I would look for room mounting the servo in the wheel well and putting a concealed control horn inside the wing on the top of the center flap. That should keep all the linkages and retracts from tangling together.
Good luck, please post your progress here I’m interested to see how it works out.
Joe