Almost a Jetpack: Is My Crazy Idea Viable?

[justsomeonenew]

Hi!

For an art project, I'm thinking of different ways to change gravity. I've already experimented several processes with video-projection / Counterweights / Electro-magnets / Dance. I had a crazy new idea and I wanted to share it with you to get your opinion.

The concept is to create a "jetpack" that reduces a person's weight. This Jetpack will not be really autonomous, it would be connected through a pipe (like the "flyboard" for example) to a huge fan that remains on the ground. So I won't really have a weight problem because the power source stays on the ground.

I imagine using a paramotor as a fan (say 70kg of thrust for a 70kg person). We then use a large metal cone of the diameter of the paramotor. We then connect a fire hose for example to the exit of the metal cone which will be connected to the stuntman with a "backpack". The air flow will be redirected downwards, which will allow the stuntman to perform incredible jumps.

I reassure you, this is hypothetical and I don't plan to make this in my garden!

Do you think the idea could be viable? What are the problems I could face? I imagine of course that there would be some air loss with this device, but it might be compensated by the acceleration of the air due to the shrinkage of the metal cone. Could the initial thrust of the paramotor be transmitted through a 10-meter pipe?

We could also imagine pressure problems in the fire hose.

Tell me what you think about it and thank you for your help!

 

[enigma]

It is possible, but it is a huge engineering problem. The biggest math difficulty will be the design of the control systems. Just a single jet fed from the ground is inherently unstable.

 

[Vanadium 50]

Wouldn't indoor skydiving be an easier way to accomplish this?

 

[jrmichler]

Your idea of funneling air from a fan into a funnel will not work because you are up against the laws of physics. Bernoulli's Law in this case.

Have you considered using water? Search water jet pack for a number of commercially available systems. Here's one that looks like it would be fun:

Jet packs using air are also available. Search jet pack to learn more. A number of people are working on this, but it is much more difficult because of the volume and velocity of air needed to get lift. Realistic solutions involve high power ducted fans or jet engines. Safety is a major challenge because there is no backup system if the power source fails and human bodies get damaged easily.

 

[justsomeonenew]

It is possible, but it is a huge engineering problem. The biggest math difficulty will be the design of the control systems. Just a single jet fed from the ground is inherently unstable.

Ok I see, the problem would be in the piloting of the device, we would have to eject the air in a more stable way, maybe with two hoses...

Wouldn't indoor skydiving be an easier way to accomplish this?

Haha ! Of course, it would be easier, but my project consists precisely in thinking a little too much about completely crazy and unusual solutions. Some solutions will undoubtedly remain at the concept stage but could still be presented as attempts.
Moreover, I may not have been totally clear but the project is not really a way to fly, but rather a way to create "lunar" gravity. The stuntman could do assisted jumps...

Thanks for your answers !

 

[justsomeonenew]

Your idea of funneling air from a fan into a funnel will not work because you are up against the laws of physics. Bernoulli's Law in this case.

Have you considered using water? Search water jet pack for a number of commercially available systems. Here's one that looks like it would be fun:Jet packs using air are also available. Search jet pack to learn more. A number of people are working on this, but it is much more difficult because of the volume and velocity of air needed to get lift. Realistic solutions involve high power ducted fans or jet engines. Safety is a major challenge because there is no backup system if the power source fails and human bodies get damaged easily.

Thank you for that answer. I'm going to find out a little more about Bernoulli's law! I'm not sure I fully understand why it's impossible to funneling air from a fan.
The idea of the project is not really a jetpack. It's more of an assisted jump system. It's a way for the stuntman to do some pretty crazy jumps. As stated in my previous message, my project consists precisely in thinking a little too much about completely crazy and unusual solutions.

It's precisely by seeing the water jetpack that I had this idea (and yes it looks really fun!). After some research, I saw that the creator had made one with air for a TV show.
In my case, I don't want a flight system, but more one to create diminished gravity.
I found this video of someone building a "similar" system.


The difference with my idea is that we don't have a turbine taped to the body, which seems a bit safer !

 

[jrmichler]

I'm going to find out a little more about Bernoulli's law!

Good!

I'm not sure I fully understand why it's impossible to funneling air from a fan.

A fan is designed to move a lot of air at low pressure. Pushing a lot of air through a funnel requires more pressure than a fan is capable of producing.

A jet engine is designed to move air at high velocity. Connecting it to a hose will create back pressure that chokes the jet. Plus the heat will melt the hose.

It's about thrust. Flying a 150 lb person needs slightly over 150 lbs of thrust. That same person with 50 to 100 lbs thrust will be able to make impressive jumps. For comparison, a powered paraglider weighting 250 lbs (wild guess) with the pilot needs about 60 to 80 lbs of thrust to fly and a 2250 lb airplane needs about 300 lbs thrust to fly in level flight.

The way to tackle this problem is to first decide exactly how much thrust you will need, then work on how to get that much thrust. The man in your first video probably has a really huge air compressor behind the wall.