When I joined PanAm, had a lot of captains ex-377, DC-6/7 drivers.
So, had a lot of questions to them.
xxx
"Captain Joe, how do you recognize a DC-6 from a DC-7...?"
"On the ground, I know, 3 blades versus 4 blades... but...?"
And the answer was...
"Son, if a plane is landing with one feathered, must be a DC-7..."
xxx
Happy contrails