RE: .o49 engines by cox
Two VERY successful planes for the $7 Sure Start are ptulmer's Das Not Ugly (DNU) and rainedave's Sure Shark. A forum search here will turn up several builds, as well as a few videos. Oh, how could I forget? The Postal Plane Project stickied at the top of the forum page is using a Sure Start as well! [X(] But of course there are many, many more planes that will fly just fine with an .049 reed valve engine, from gliders to trainers, to warbirds and pylon racers... depends on wing area and all up weight of course. For what it's worth, I recently converted a Parkzone J3 Cub to a Cox .049 and at 15 oz, it flew like a scaled cat.
All Cox engines love fuel with medium to high nitro content (15-35%) and a fairly high oil content (20-25%) of which should be mostly castor oil.
Hope some of this helps,
-Joe