The answer to that goes back many years.When free flight was the only way you could fly a model there were classes established A, B,C and I think D with engine size from smallest to largest... Class A was .09to .18 Ithink. Well technology caught up with the engine sizes and sometime in the late 40's after the invention of the glow plug folks started making these little engines that were called 1/2A.Currently that is any engine of .049 displacement and smaller by the AMA rule book. That said many modelers lump in anything smaller than a 09 or maybe even 15 into a general small engine class. So maybe more correctly your design looks great for a small engine but maybe just a bit big for an 049. Take a look at the wing spans and area on the
www.brodak.com website for some general ideas about what size works for what engine.
Bob