https://en.wikipedia.org/wiki/Turbo-compound_engine
Aircraft piston-engine swan song. Killed by the turboprop, a full-blown turbine not connected to a piston engine. Ironically, turboprops benefited from technological advances made by... turbine-boosted piston engines. Such as P-47 and P-38.
It went this way
- compressors driven by the piston engine itself (Allison V-1710, Merlin, Griffon)
- compressors driven by a turbine, a turbine driven by the piston engine exhaust gases (R-2800, R-3350, R-4360, turbocompound)
- turboprop: turbine connected to a propeller, without a piston engine (Tyne)
- jet engine: gone is the propeller.
Turbocompoud piston-engines are like the last, advanced steam locomotives, or the last ocean liners like France: perfected to near perfection, but nonetheless obsolete, pushed by the wayside by a more advanced, simple technology.