MATH!
Going with a human weighing 150 pounds, the fart would need to produce over that many pounds of force per second, so going with 200 pounds of force (just a nice round number), and the goal of, say, 5 seconds, you’d need to be able to generate 1000 pounds of force.
The good news is that, based on the circumference of the, er, “outlet valve”, you wouldn’t need to carry 1000 pounds worth of gas. You’d just have to calculate the PSI and go from there. That I’d have to leave to someone smarter than I am.
Superman’s ability to fly, explained?