I used the SK .91 two stroke and used a shoe horn to get it installed, that and a sanding wheel plus I didn't taper the nose as much as normal. Because it's a build you can come up with a lot of ways to do it. The class-C was limited to a .61 as I recall. The plane was designed for speed before the turn around pattern came about. The DBs I have flown will out perform the Kaos in the knife edge every time. Looks really cool with retracts. One of my spring airs isn't working so I went with wire gear. The build is normal for the times. No photos of part A slipping into part B. The instructions just call for a piece of 1/16 X 3 sheeting but don't say what length to cut it from. Just a lot of thinking needed for the build.