RE: PROFI RAMBLER .049
The smallest I've ever gone was 105 sq inches with a TD .049 on bladder. It was a pusher / flying wing with wingtip fins. I don't remember what it weighed, but this was back in the GWS RX / HS55 / 90 mah nicad days...plus it was covered with red cellophane.
This is the plane that I carved a maple 4x4 prop and kept shaving the blades to see rpm gain. Finally it threw 1 blade in flight and it sounded like someone hit the nitrous switch. After it landed I discovered the missing blade and flew it like that the rest of the day until the other blade broke on a landing.