I've been thinking about the possibility of an aerobatic part 103 ultralight. Pretty much just using a 103 appendix 7 spreadsheet and drawing napkin sketches so far. Looks like assuming a 170 lb pilot and a 254 lb plane you need at least around 120 ft^2 for a double surface wing with 50% or more flaps. Doing it as a biplane lets you brace everything and get the spar bending loads low. Haven't done any structural calcs beyond just that. Liked the looks of this one enough to build it in x-plane as a test of the basic idea: Cute little thing. 16 ft span upper, 14 lower, 4 foot chord (including the part inside the fuse as wing area). Just assumed I can put a Verner 3V on it. Flys pretty good. With full span flaperons on all four wings roll rate is over 360 deg/second. Climb isn't spectacular, but about the same as the 152s I used to fly. Then, I go into the settings->Weight and Fuel. It defaults to half the max load. So put in all 5 gallons of gas, and a 255 lb pilot instead of the 150lber it defaulted to. Won't even climb out of ground effect. Start it in the air it won't maintain altitude on the full 40 hp much less the 34 "max continuous". So, if I'm going to build something for me to fly (instead of some hypothetical average pilot) I need more wing, less drag and probably more power. Doubt the weight budget would let me put a bigger engine on it. Back do the drawing board for this one. Was a fun little lesson for me, thought I'd share.