Originally Posted by
barit1
Stepping back a couple decades, the R-2800 18-cylinder aircooled piston engine presented a cooling challenge, and the cooling drag was substantial. But it was a reliable and well-respected machine and successful in the DC-6, Martinliners, and Convair twins.
Convair took a different approach to cooling it, and ducted the engine exhaust into augmenter (eductor, if you will) tubes in the aft nacelle, where the cooling air was drawn out at the wing trailing edge.
I doubt this created any thrust in itself, but since it improved cooling with less external drag, it had the same overall effect as a small jet.
For what it's worth, Douglas manuals for the DC-6 used to claim that they got 600 lb (IIRC) of "jet thrust" from the exhaust. It never seemed to me like it was a particularly useful piece of information, so I don't know why Douglas felt compelled to print it in their manuals, but I do recall running into that bit of trivia back when I was flying the DC-6.