Real Water Rocket Guy – Analysis to come
[S]eems like something that would be on Swans on Tea
Well, now it is
Rhett now has a detailed analysis posted in which he explains how the thrust is generated, and estimates the power the pump must have to do this.
One thing to note about this is that it works because much of the propellant is not being carried onboard. The rocket is lifting the water in the feeder hose, but that’s all — after a few seconds, that water has been expelled. But the jetpack continues to fly, because additional water is being supplied. This is one of the big problems for rockets. They need to carry enough propellant to lift the payload, and all of the propellant and fuel (for some systems, e.g. ion drives, the propellant and the energy source aren’t the same thing). This is why rockets are really inefficient, and have such a small ratio of payload/rocket mass.
He carefully calculated that it would require 800hp. He didn’t question for an instant the feasibilty of putting an 800 hp recip engine and pump in the little jet ski thing the guy is dragging behind him. What amazes me is how well they digitally airbrushed the cable to the helicopter.