Just another research update.. I spoke ( email ) with Dennis of Aerolite 103, he said that they are going to start flight testing a 4 stroke on the Aerolite 103 in the spring. I belive he said it's going to be a "Vangard" engine? Not sure if i'm spelling it right. Is anyone familiar with these engines? I also looked at the Belite, and the true legal UL only has a Hirth F33 available. Belite also has folding wings, according to their site, but not sure how hard it would be to fold and unfold. It looks like the BYF just takes a couple minutes to rotate the wing. I emailed BYF a couple of times, trying to get information, but can NOT get anyone to respond. I'm still checking a few out, but so far, the BYF is my favorite UL.. and of course, it has to be the most expensive!