As far as I know airships, specifically rigid-airships, do not have an upper size limit other than what is required by practicality and how willing you are to build gigantic airship sheds. But one question that has been burning inside me recently is how small can an airship, specifically a non rigid airship or blimp, feasibly be and still fly.
I know there is a minimum amount of lifting gas needed but I have never received a straight answer. In the real world, the smallest airship that I know of is Gallagher's airship the White Dwarf. It is about 48 feet long and 17 feet wide with a 17 foot long gondola and 6200 cubic feet of lifting gas capable of lifting almost 400 pounds. The airship is pedal powered so It can't go fast, but in an article I read on Google books it managed to reach 1200 feet in the air.
Granted, the blimp had been caught by the wind which made it rise to that height but the blimp managed to maintain the height for a few minutes before descending. With the White Dwarf as a reference, what do you think the smallest possible airship (envelope) size is for personal travel? Assume that it is powered by a lightweight magnesium aluminium motor, like that of a motorcycle (light enough to be carried by the average guy), has a 5-7 foot long gondola made from a magnesium aluminium alloy, has a traditional cigar, football, or teardrop shaped envelope, and has enough lifting gas to lift someone off the ground and achieve a maximum Height of 300 to 650 feet using either hydrogen, helium, or hot air.