Hi Kibet,

To answer your question directly, I'm not aware of any design ratios that are specific to Part 103 ultralights. The combination of 254 lb empty weight and 28mph max stall speed (from the Part 103 regulation) tend to force most designs to some similar design values. I would say that the most common design value that you will find is a main wing surface area S = b x c ~= 115 ft^2 where b is wing span and c is wing chord. This value can vary based on flap type/size or flaperon usage.

Engine power can vary widely. Common values range from 27HP to 50HP. Generally designers will put the largest engine they can on the ultralight but still remain below the 254 lb empty weight limit.

Hope this helps.