Strange as this contraption appears to be, it actually has a lot in common with your ordinary turbocharged piston engine. The relative sizes of the components are different, and so is the arrangement of what is “drivingly connected” to what, but the building blocks are the same. A turbocharger consists of a turbine and a compressor on a common shaft; the turbine captures energy from the exhaust stream and uses it to compress the induction air. In this case, the engine drives the propeller; in the rotary-turbofan hybrid, the turbine drives the propeller (called “fan,” but it’s the same thing: a bunch of spinning wings producing forward lift) while the engine drives the compressor. But it doesn’t really matter what drives what, any more than it matters, when you’re building a house, who hammers, who saws and who cleans up. A certain amount of work needs to be done, and three workers are there to do it.