When Raymond Li decided to build a jetpack propelled by water instead of rocket fuel, most of his friends thought he had gone crazy. Worse, engineers told him it would be impossible to manage the water's mass and thrust to keep it stable in the air.rnLi, however, figured that if he attached a hose to his pack, and put the engine and water pump in a separate vessel that dragged behind him, he could seriously reduce his weight, and therefore the amount of thrust needed to stay aloft. In theory, a stiff hose filled with heavy, pressurized water would also add drag to stabilize the jetpack for better forward flight control.
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