In my world, humans have the innate power to fly.

This is a supernatural power, like superheroes, so there's no scientific explanation.

However, they still need oxygen to breathe, G-force is still a consideration and other physical limitations remain.

I'm interested in what these limitation would be, supposing that humans are not using any technology to boost their flight capabilities and they have no speed or weight limit?

Here is a list of questions but it's in no way exhaustive:

  • What's the maximum G-force a human could sustain? Roughly 75G
  • What's the maximum altitude they could reach? I think 8000m because of oxygen but maybe temperature would be a bigger problem.
  • What's the maximum speed they could attain before damaging their bodies/dying, assuming acceleration is not too hard?
  • Does air friction become a problem at a certain speed? I'm assuming yes.
  • $\begingroup$ "humans are not using any technology" What constitutes "a technology"? Aviator jacket, goggles, gas mask? $\endgroup$
    – Alexander
    Oct 9, 2020 at 17:12
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    $\begingroup$ Hello Gary. A quick search of our Stack will show you that a lot of questions have been asked about humans with the ability to fly including limitations, which is why I VTC'd needs details. Note that I could have also VTC'd for needs focus. You're supposed to ask only one question. $\endgroup$
    – JBH
    Oct 9, 2020 at 19:58
  • $\begingroup$ How much weight can they carry while still flying? 0 and they need to be nude to fly? 5lbs? 50lbs? The limitations change for someone in street clothes vs a winter coat vs modern fighter pilot gear complete with pressure to counteract g force. I assume if everyone can fly such suits would be more prevalent than a smartphone today. $\endgroup$
    – TCooper
    Oct 9, 2020 at 23:12
  • $\begingroup$ Do they have wings or do they fly like Superman? $\endgroup$ Oct 9, 2020 at 23:21

2 Answers 2


Temperature: As altitude increases, temperature decreases, by about 2 degrees C per 1000 feet above sea level. Temperatures will dip below freezing at around 7,500 feet up, so you'd probably want to stay quite a bit below that or risk frostbite. Especially with windchill, any exposed skin will be at risk. This temperature change occurs relative to ambient temperature at the ground, so you could go a bit higher relative to sea level if you're in a very warm area, or if you're in an area with a high elevation, which will be somewhat warmer than just air at the same elevation.

Oxygen: The amount of available oxygen decreases with altitude. The FAA requires pilots to use supplemental oxygen at cabin pressures above 12,500 feet for 30 minutes, on the assumption that the plane will immediately dive to an altitude with breathable air pressures upon loss of pressure, and at all times at cabin pressures above 15,000 feet. You begin experiencing notable reductions in performance from hypoxia above 11,400 feet, though the time of useful consciousness remains indefinite until 15,000 feet, beyond which it begins rapidly declining.

G-force: This is mostly a non-issue - so long as you're not speeding up, stopping, or turning too quickly, you can keep your G-forces at manageable levels. The biggest limitation will be your turning radius at high speeds.

Top speed: Since these people can accelerate without bound, their maximum speed is theoretically unlimited. Once breaking the sound barrier, however, there will be significant heating due to air resistance, as pressure increases dramatically once you are flying into your own shockwave. According to this question, speeds in the range of a few thousand km/h could cause heating in the range of hundreds of degrees C. Air density decreases with altitude, however, so you will be able to go faster at higher altitudes. At any rate, the sonic boom when breaking the sound barrier will also be quite unpleasant, so you probably want to keep it under Mach 1 (1234 km/h). I'll also mention that even windspeeds in the low hundreds of km/h can be very damaging, uprooting trees and leveling homes. Unless you're wearing specialized skintight clothing, whatever you're wearing will likely get ripped to shreds if you're flying faster than perhaps 300 km/h - I hope you don't mind arriving naked.

Overall, humans without any special equipment might be limited to flying at sub-sonic speeds under 1000km/h, and may only be able to fly at a couple of hundred km/h comfortably. Top altitudes will be about 5000 feet, depending on local climate and geography. With warm clothes and flying at low speeds, one could perhaps get up to 15,000 feet in altitude before availability of oxygen starts to become a big issue. Otherwise, the limiting factors will be air resistance for speed, and temperature for altitude. Since these work oppositely (altitude makes you too cold, speed makes you too hot), you might be able to balance these somewhat to go faster at higher altitudes, but you'd probably need to be spinning constantly like a rotisserie chicken (since only your front side is being heated) and you'd risk burns or frostbite if the temperature balance didn't work out just right.

  • $\begingroup$ "Tempertatures will dip below freezing at around 2.5km up"... citation? Is that "above ground level" or absolute elevation? Is there a significant difference between being near the ground at that elevation vs. having a few km of air under you? I ask because 2.5 km is ~8,000 ft, almost 3,000 ft below treeline in e.g. the Rocky Mountains, and I'm pretty sure it isn't freezing (not during the day in summer, anyway) there... $\endgroup$
    – Matthew
    Oct 9, 2020 at 16:35
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    $\begingroup$ @Matthew Good point. I'm referring to temperature changes with each additional km of altitude, so it makes sense to start counting from ambient temperature at ground level. Temperatures will be higher near the ground due to warmth from the land, so land with a high elevation will be warmer than air above sea level with the same elevation. Climbing a mountain would likely result in somewhat lower temperature changes compared to going straight up in a hot air balloon, for example. $\endgroup$ Oct 9, 2020 at 16:43
  • $\begingroup$ @Matthew: On the other hand, temperatures are consistently below freezing for several months of the year in the more pleasant parts of the Earth, including most of the Rocky Mountains. But flying would be rather like cross-country skiing: the exercise keeps you warm. $\endgroup$
    – jamesqf
    Oct 9, 2020 at 16:45
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    $\begingroup$ Upvoted for "spinning like a rotisserie chicken". $\endgroup$
    – John O
    Oct 9, 2020 at 16:53
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    $\begingroup$ I'd think it become difficult to breath unassisted, well before 1000 km/h. $\endgroup$
    – Daron
    Oct 9, 2020 at 17:07

Orientation: when earth isn't visible pilots can't reliably determine their height, speed and and bearing and must rely on instruments. Unaugmented humans would get lost in clouds easily, with risk flying into ground at high velocity. Even without clouds, over monotone bare rocks or calm water it can be hard to judge safe flying height. Without navigation experience it is also possible to fly in circles and starve.


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