arrrr slave boss is on a zeppelin powered lifted by the warmth his own farts into its canvas
slave boss: "human methane is more environmentall sound than hydrogen. it is warm, and can be burned for fuel. be sure to have humans distant from it when burning it."
he's near the ground hanging from it and eating an english muffin
it turns out farts even contain hydrogen
so maybe you could fart into a giant zero-pressure balloon up in the air and the heavy sulfites might fall out the bottom and the hydrogen lift to the top, lifting you !
if we trust web search engine summaries (not sure i would advise to) then - a fart is maybe 20% hydrogen - a fart contains about 1 liter of gas - a person farts maybe 10 times a day if we assume the 20% is by volume, then that's 2 liters of hydrogen per day for every passenger!