Can Humans Achieve Flight Through Theory Crafting?

[Eden Hazard]

Hi, smart people

This quarantine has got me thinking: Can we get people in the air? I have 3 questions that may or may not help answer this question. But I do appreciate any insight.

1. How would one accelerate (the average human) 100 feet in the air and sustain their position? Under normal conditions (earth gravity etc)

2. What would one need to levitate a human (e.g. a foot off the ground) using some type of pneumatic system?

3. What pressure/volume/temperature/type of gas would one need to levitate a human (e.g. a foot off the ground) by propelling the gas at the ground as thrust?

Thank you

 

[russ_watters]

Welcome to PF! Have you googled "human powered flight"? You'll get a lot of good hits...

Bottom line is it's been done, but you have to be a serious cyclist to produce enough power to do it.

[Late Edit] I may have misread this as human powered flight. If it's just humans flying, we have a lot of ways of accomplishing this.

 

[Baluncore]

Are you considering only human powered lift, or other sources of energy also.

Hovercraft, helicopter, jetpack, ground-effect aircraft, hot air balloon.

Human-powered ground-effect would be possible, but also dangerous in windy weather.
https://en.wikipedia.org/wiki/Ground-effect_vehicle

 

[jbriggs444]

What pressure/volume/temperature/type of gas would one need to levitate a human (e.g. a foot off the ground) by propelling the gas at the ground as thrust?

Say that you are a 50 kg human. You can levitate yourself by hurling 50 kg of rocks downward at 9.8 meters per second every second. [Let's round that up to 10 meters per second]

That takes a fair bit of energy input and a lot of rocks. One can calculate the required power using the formula $$E=\frac{1}{2}mv^2$$ You start with the mass flow rate (50 kg/sec in this case). That's your m. And you factor in the exhaust velocity (10 meters/sec in this case). That's your v. You calculate E and that's the energy that you have to supply every second.

If we relabel the variables as $P$ for power, $\dot{m}$ for mass flow rate and $v_e$ for exhaust velocity, we get$$P=\frac{1}{2}\dot{m}v_e^2$$In the case at hand, that's $\frac{1}{2}50\ 10^2 = 2500$. For mass flow rate in kg/sec and exhaust velocity in meters/sec, the result is in joules/sec = watts.

A human can only produce in the neighborhood of 100 watts sustained. So in addition to requiring too many rocks, this approach requires too much power.

What if we tried to reduce the rock requirement by throwing them harder? We could throw 25 kg of rocks downward at 20 meters per second. We've cut the mass flow rate in half by doubling the exhaust velocity. Bummer, dude. If you run the numbers, it now requires 5000 watts. The required power is directly proportional to exhaust velocity.

If you want to get the power requirements down, you have to reduce the exhaust velocity. And you can forget about carrying the rocks. So you have to force some air downward. If we want to get 2500 watts down to 100 watts, we have to reduce the exhaust velocity by a factor of 25. From 10 meters per second to 0.4 meters per second. And we have to increase the flow rate from 50 kg/sec up to 1250 kg/sec. If we're going to do this with air, that's a honking lot of air to move.

You need a huge helicopter. Impractically huge.

 

[anorlunda]

The OP question sounds like these vertical wind tunnel rides.

 

[Lnewqban]

...
2. What would one need to levitate a human (e.g. a foot off the ground) using some type of pneumatic system?

Vertical duct.
Vertical blower.
Man inside ascending vertical airstream inside duct.
Velocity of airstream should be close to terminal velocity.

Please, see:
https://en.wikipedia.org/wiki/Terminal_velocity

 

[jrmichler]

You need a huge helicopter. Impractically huge.

But possible. Just barely: https://en.wikipedia.org/wiki/Human-powered_helicopter

 

[phinds]

But possible. Just barely: https://en.wikipedia.org/wiki/Human-powered_helicopter

Amazing.

 

[russ_watters]

I added a late edit to my first post: I may have misread the OP as being about human powered flight. If it's just humans flying, we of course have a lot of ways of accomplishing this. If the question is about a single person flying machine, there are several, from personal hovercraft to wing suits, ultralight, jetpacks, etc. The OP will need to clarify the constraints.

 

[Eden Hazard]

I added a late edit to my first post: I may have misread the OP as being about human powered flight. If it's just humans flying, we of course have a lot of ways of accomplishing this. If the question is about a single person flying machine, there are several, from personal hovercraft to wing suits, ultralight, jetpacks, etc. The OP will need to clarify the constraints.

Right. Thanks for all the insight so far. If we wanted to get people hundreds of feet in the air, I wouldn't want to be relying on human power generation so there would need to be an external power unit on the flier. The user should be able to freely control their velocity in the air. There are some real developments that are chasing this idea. Also, say we wanted their flight time to be 20 minutes before they would have to come back down.

But the thing is, we'd want the flier to be able to move freely like uh Superman. But I don't know much about the the combustion that's happening internally in the 2 links I've sent below.



https://gravity.co/



Thank you

 

[Filip Larsen]

For power human flight its hard to not be impressed by the Flyboard Air or jet powered wing-suit that many now are flying:

 

[Baluncore]

If we wanted to get people hundreds of feet in the air, I wouldn't want to be relying on human power generation so there would need to be an external power unit on the flier. The user should be able to freely control their velocity in the air. There are some real developments that are chasing this idea. Also, say we wanted their flight time to be 20 minutes before they would have to come back down.

Why does anyone need to take the risk? Who would be so foolish?
It is not the power you need to climb that is the limiting factor, it is the reliability of the parachute. A free fall from 30 feet will kill most people.

 

[russ_watters]

Right. Thanks for all the insight so far. If we wanted to get people hundreds of feet in the air, I wouldn't want to be relying on human power generation so there would need to be an external power unit on the flier. The user should be able to freely control their velocity in the air. There are some real developments that are chasing this idea. Also, say we wanted their flight time to be 20 minutes before they would have to come back down.

But the thing is, we'd want the flier to be able to move freely like uh Superman. But I don't know much about the the combustion that's happening internally in the 2 links I've sent below.

It's basically just a really small airplane, with really small jet engines.

 

[Filip Larsen]

Regarding safety in case of engine-out it is a significant bonus to have a passive lift generating device (e.g. wings or a paraglider) instead of lift being generated only by said engine (like on the Flyboard Air).

Wings also helps a lot in reducing the needed power for sustained flight. For instance, a standard light single-seat glider may only need around 200 W to stay at altitude whereas a human on a wingless platform would need at least 5-10 times that.