Related to Perpetual motion machines and rocketry.
In my current worldbuilding project, people commonly employ enigmatic Clarkean machines called "spinners". They are two adjoined cubes, counter-rotating and effectively unstoppable. No amount of counter-torque can slow their rate of rotation. In addition, the speed at which the cubes rotate against each other can be "programmed" through a dizzying and convoluted series of mathematical instructions--a two-way mathematical dialogue via EM communication, where difficulty steps up in tandem with faster rotation. Some people have spent their entire lives unraveling and refining the rules that coax spinners up to greater and greater speeds.
Spinners are used in everything from portable heaters and electricity to vehicles and aircraft. Simple, dumb control circuitry can encourage lesser speeds from spinners, while the greatest speeds require computers of vast capability.
(In addition to speed, size may also be ordered in this way. Each cube is by default 20 cm to a side--about the span of 2 credit cards. They can be ordered to twice that in width and height and six times that in "length" parallel to the rotation axis. From two 20x20x20 cm cubes to two 40x40x120 cm rectangular "rods", and anywhere in between. It's also important to note that spinners have tensile & compressive strengths greater than any manmade material, they don't experience creep or stress deformation, and they start vaporizing at 8000 K.)
My civilization is entering an age of high-altitude and orbital flight, and I would expect the application of these magical spinners may reach far into that domain. A fully extended spinner, two rectangular bars each twice as wide/high as a hand and over a meter long, may deliver an enormous amount of torque.
Aviation is outside my familiar research. Originally, I imagined a fan-powered supersonic aircraft, but as I started to look into it I saw a lot of doubt about whether a fan motor could do any useful work with a supersonic intake. Some comments I've seen say it is impossible. Supersonic shocks on the fan blades would cut the flight short and ensure a rough landing, no known material could withstand the stresses.
My previous question asked about rocket flight and how spinners would be involved in producing thrust with fuel and out of an atmosphere. This question is somewhat the opposite: how spinners may be used in producing thrust without fuel and in an atmosphere--supersonically. Is my spinner-powered, supersonic fan motor impossible, or is that an unqualified conjecture? Is there a better hypothetical way to use spinners to achieve supersonic flight?