Hey guys, I'm in the middle of building a Part 103 Ultralight of my own design... and I think I'm hooked on this aircraft design stuff! Anyway, I'm now starting to dream of designs for larger planes (4-6 place). Can you guys point me in the right direction to find the requirements I must meet here in the United States? I've just started sifting through the Federal Aviation Regulations... but I'm getting no-place fast. :depressed Also is there a difference for a twin vs. a single engine in the regulations?