Hi John,
The scale Airfoil should make no difference, My U-2's Horizontal Stabilizer has an invert airfoil much like the original (Just I made an error of having it too thick). The Real U-2 has a NACA 63a409 (which is 9% thickness) and the tip is the NACA63a406 (which is 6%) , this shouldn't relate to any washout, as 3% will effect the slight under camber at the trailing edge only. I went for the easier option and used a Reynolds number airfoil for the speed I was aiming at. This will only affect the Stall Characteristics of the wing, but they are so long anyway, you won't really need to worry about stall with a motor once it's airborne. Tip Stalling, isn't really going to happen it's so long, but as in my case you can stall the wing...

Regarding Flaps, My Flaps use normal 6mm Robart Dowel Hinges at 45 Degrees at the Bottom of the hinge line, this provides a scale, I took pictures of the Full Size at RAF Fairford a few years Back, so 80% of what is on my aircraft is as close to scale as simplicity would allow,being basically a prototype. have look at this pic, [link=http://www.clubhyper.com/reference/u2sfiles/U-2S_DragonLady-63.jpg]Left wing Flap[/link] , the flap is fared on top and bottom with a off centered middle hinge point, with a Perfect Fit. You can do what I did because you won't even notice the extra effort this will take. overall on the wings, I didn't spend much time making it 100% scale, it just has to look the part.

The Biggest Part of Advice I can offer is make the LIGHT, I added 3lbs Lead to the nose which I wasn't counting on and that added to the overall weight from my projected 17lbs... REALLY DEPRESSING.

Retract, I used a SOLID Aluminum F-86 nose gear retract from Trim aircraft [link=http://www.trimair.com.au]Trim Aircraft[/link], it's got very little in the way of steering, but it's super strong and best of all it's thinner then any of the units from BVM, YELLOW, ETC, which I tried, the rear unit is a spring air Retract. The smaller the version of the U-2 the less space, the at 12th Scale the TR2 / U-2R the Fuz is about 20% narrower and smaller, making evening a tight fit.