Could a Pneumatic Jet-Pack Powered by Pressurized Water Work?

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Discussion Overview

The discussion revolves around the feasibility of a pneumatic jet-pack powered by pressurized water, exploring concepts of thrust generation, water flow, and the mechanics of flight. Participants engage in both theoretical considerations and practical implications of such a device.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant proposes using a PVC pipe filled with water and pressurized air to generate thrust, calculating potential thrust based on pressure and area.
  • Another participant questions whether the concept is akin to a bottle rocket, suggesting a need for clarity on the design's intent.
  • Some participants reference a Mythbusters episode, implying prior exploration of similar concepts.
  • There is a discussion on the relationship between thrust, body weight, and flight, with one participant stating that thrust must exceed body weight for vertical take-off.
  • Another participant confirms the calculation of thrust based on pressure and area, agreeing with the thrust values presented.
  • A participant seeks guidance on calculating the rate of water usage, expressing concern over the balance of pressure and water supply for effective thrust.

Areas of Agreement / Disagreement

Participants generally agree on the basic principles of thrust generation and the need for thrust to exceed body weight for flight. However, there are competing views on the practicality and design of the proposed jet-pack, and the discussion remains unresolved regarding the specifics of water usage and pressure management.

Contextual Notes

Participants express varying levels of familiarity with physics concepts, and some calculations rely on assumptions that may not be fully explored. The discussion includes references to pressure and thrust calculations but lacks detailed formulas for water usage rates.

Who May Find This Useful

Individuals interested in experimental physics, engineering design, and the mechanics of flight may find this discussion relevant.

bwheeler96
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I would think someone would have thought about this already, I'm not taking physics so forgive my assumptions about water flow, thrust etc. but, If I were to say... take a 12" I.D. 24" section of PVC Pipe filled about 85% of the way, 6^2*3.14*24/231*.85 = so about 10 gallons, 80 pounds of water for our purposes. The remainder being air pressurized to about 200psi, the water then going through an opening of about 3in^2, for every square inch i should get 200 pounds of thrust to start with, so 600 total right off the bat, and then dropping off rapidly thereafter? Any corrections/comments, would this work?
 
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Forget jetpack, are we talking about a bottle rocket?
 
If you have not yet watched the mythbusters episode on this, please do.
 
russ_watters said:
If you have not yet watched the mythbusters episode on this, please do.

Will do, I understand the jetpack is a "better in theory" idea i just thought that with pneumatics, and i little innovativeness the weight of a jet could be eliminated and a substantial amount of thrust could still be achieved
 
bwheeler96 said:
Will do, I understand the jetpack is a "better in theory" idea i just thought that with pneumatics, and i little innovativeness the weight of a jet could be eliminated and a substantial amount of thrust could still be achieved

You mean "jet" as in airliner?

A substantial amount of thrust would provide a lovely boost, but unless you follow that with an amount of thrust required for flight it means nothing. If you don't you're just a glorified bullet.
 
Amount of thrust required for flight must be > body weight, correct? And from there the more thrust you have, the faster you will accelerate/your top speed will increase? also if 150 p.s.i. of pressure is pushing water through a 3 square inch opening that mean 450 lbs of thrust yes?

Note: I understand that generally we should use kg for this type of thing but I am still getting used to using kg so please work with me here
 
bwheeler96 said:
Amount of thrust required for flight must be > body weight, correct?

Assuming we're talking vertical take-off (helicopter style) then yes. For hover, thrust = weight.
And from there the more thrust you have, the faster you will accelerate

Yes
your top speed will increase?

Not necessarily.
also if 150 p.s.i. of pressure is pushing water through a 3 square inch opening that mean 450 lbs of thrust yes?

Pressure = Force / Area

So Force = Pressure x Area = 150 x 3 = 450lbf. Sounds good to me.
 
Thanks a ton, I really appreciate all the help. Now how would i go about calculating the rate of water usage? I can't find much on this and I saw a video with too much pressure and not enough water, the guy had plenty of thrust but this did not end well. Any formula for this?
 

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