In my PanAm days, I flew with number of ex DC-6/DC-7 captains and flight engineers.
Even some B-377 guys as well...
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One time, I asked them how to recognize a DC-6 from a DC-7.
On the ramp, easy, the DC-6 had 3 blades propellers, the DC-7 had 4 blades...
But when they are flying...?
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They told me -
"If one is landing with a feathered engine, has to be a Seven...!"
Apparently, the R-2800 was a great engine, but the R-3350 was another story.
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Happy contrails