What's wrong with this math: A lot of thrust and almost no fuel?

AI Thread Summary
The discussion centers on the feasibility of achieving significant thrust with minimal fuel using high-pressure gas ejection. A force of 1500 N and a velocity of 200 m/s could theoretically be achieved with a mass flow rate of 0.0007 kg/s at 15 MPa pressure. Questions arise regarding the practicality of a 1 cm² nozzle at this pressure, the calculation of effective velocity without combustion, and the counterintuitive negative mass loss rate with increased pressure. The original calculations were based on combustion assumptions, leading to misunderstandings about the physics involved. The conversation highlights the complexities of propulsion physics and the need for accurate modeling in such scenarios.
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Using basic calculator it seems as if a rocket can produce a lot of thrust and use little fuel if you increase pressure within practically possible range:10-20MPA?
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So according to this if you need a force that can lift a human and even an extremely ultra-light craft (1500 N) and have a velocity of 200 m/s you can eject extremely small amount of fuel through the nozzle: 0.0007 or less kg per second for as long as you're using 15 MPa pressure which is doable and even storage cylinders on alibaba use it. Another calculator shows that hydrogen stored at the same pressure will have just 18.5 kg weight per cubic meter? So this gives over 7 hours flight time with 720km/h??

Several things I don't understand: is 1cm^2 nozzle with 15.1 Mpa pressure possible? How is the effective velocity calculated especially if you aren't combusting but just open cylinder to release pressure? Why is the mass loss rate negative if you increase pressure? I should've solved this as a polynomial calculation since the calculator gives odd values unless you reload. Thank you.
 
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The tool is assuming combustion, not a high pressure reservoir so your assumptions about what things mean is off.
 
^ Yeah...that's what I was suspecting...
 
[A trolling follow-up post by the OP has been deleted, and this thread will now be closed]
 
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