I was questioning the efficiency of turbo-props vs turbo-fans. The only difference between the two is that turbo-props are connected to the shaft of a jet via a mechanical linkage rather than directly to the shaft as a turbo-fan is.
This article says that both props and fans are more efficient than a jet alone. Although, I would guess that there is some more loss in the mechanical linkage of a prop than in a fan.
https://www.boldmethod.com/learn-to-fly/systems/the-4-types-of-turbine-engines/
A pretty good article, by the way.
Hughes’ objection to jets was actually well founded. He argued that jets are only efficient at high altitudes and speeds. A part of a flight envelope that commercial airliners spend little time, if they enter them at all on shorter routes. He kept props (even though they were the ridiculous high-maintenance dozens of cylinder rotaries) until they stopped being produced. He was okay with turbo-props on helicopters and even automobiles. Of course, turbo-fans were decades away from being developed. They came into their own during the fuel crisis of the 1970’s and due to noise issues with turbo-jets at busy airports. So, like you said, mostly efficiency.
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