Hi, thank you for your great reply. But in that video you’re citing, the turbine is being used as a turbojet, whose high exhaust velocity is a complete mismatch with the travel velocity being sought, and therefore comparatively inefficient. A high-bypass turbofan might have better fuel economy, and a turbo-prop would likely have even better fuel-economy than that – which is the reason why militaries around the world are trying to come up with small turbines as propulsion systems for UAV drones.
As an alternative to the turbine, what about the rotary piston engine? The most common type of rotary piston engine is the Wankel rotary engine. It is known to produce less vibration and noise compared to reciprocating piston engines, while also having a higher power-to-weight ratio. But the Wankel rotary engine tends to have inferior compression ratio, rooted in problems maintaining its seals. However, a company called Liquid Piston has recently come out with a new design for the rotary engine featuring an inverse geometry.
The US military and DARPA have funded development of this engine for possible use in drones and auxiliary power generators.