Future forms of propulsion

I hope this thread to be a place where we can talk about things from solid state batteries, fuel cells, capacitors, engines, motors, and every other future form of paramotor propulsion that we can think of.

I have been thinking about flywheel propulsion for a long time. Back in the 50´s they where used in buses and gave a 6 km range with top speeds of over 50 kmh and more recently they have been looked at as a way of clean and cheap energy storage. I have been thinking of using them to power a paramotor so I decided to dig in a bit more. Currently the world record for the fastest flywheel surface speed is just over 3100 mph so i will pretend that in the future we could build an air worthy flywheel that could handle this. Plugging some numbers into a fancy online calculator I was surprised to see that if you could spin two counter rotating(cancels net gyroscopic effect) 15 pound, 12 inch diameter cylinders/pancakes at 84k rpm you could store nearly 1.7 kwh energy in it. Even better, if you could design the same weight and diameter flywheels into rings, you could get closer to 3.4 kwh. To top it all of you could charge it as fast as the motor/generator in it could handle which could be as little as 4 minutes(25 kw motor w/ 1.6 kwh flywheel), it could handle nearly indefinite charge and discharge cycles, would give no voltage sag, and it could actually be more efficient than a battery.

I would defiantly put this into the future category as we have not developed motors/generators that operate at the required power and rpms while maintaining a reasonable weight, The flywheels would instantly shatter going around corners due to the enormous gyroscopic effect felt by the flywheels combined with the thousands of Gś trying to pull them apart, and finally these flywheels need magnetic bearings which I don´t believe have been properly developed for this scale and this much gyroscopic force.