I have been contemplating adding flaps to my H9 60 as well. There is a great article in Flying Models magazine, MAY 2003 edition. It has a write up on the H9 60 mustang, and the guy modified it for flaps. It looks fairly simple, with some work! The wing is built up! You cut a straight line from the inboard tip of the aileron, about 15" towards the fuse. On the bottom, you will cut about 1/2 inch aft and parrallel to the aileron towards the fuse. In other words, make the cut for the bottom of the flap, 1/2" from the cut on the top! This will allow you to hinge the flap at the top and for a bevel to be formed, for the downword swing of the flap. Its a typical flap design. You will have to cut the flaps out, cutting through ribs, then filling in with 1/4" balsa pieces in between the ribs to strengthen it. I have not done this mod yet, but Im very tempeted! It can be done, and sounds from the article, worth the effort! Good luck!