Thanks Mike, it is tricky I must admit, what does work quite well is stitching two pieces of film together "sticky side to sticky side". This gives a strip about 1" wide, the sewn strips are then ironed on to the wing and aileron. This is done before covering preferably. The line of stitches gives a near perfect alignment of the aileron, I'll tack on some photos when I get to the exciting bit of adding the control surfaces. I've used clear tape in the past, but only on a glider. Is it still available? Haven't seen it for a while.