[Fraxinus]

Would not using a six bladed prop be lighter and less complex than two counter rotating 3 bladed props and thus be more efficient, even with the torque issues?

[az_gila]

Would not using a six bladed prop be lighter and less complex than two counter rotating 3 bladed props and thus be more efficient, even with the torque issues?

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Not sure, but this wiki article gives a brief explanation. It seems the gain is by the air exiting the prop swept area not having any rotational component.

https://en.wikipedia.org/wiki/Contra-rotating_propellers

[Little Pig]

If I had to guess, the counter-rotating props might add some advantage in overcoming the various effects of the GAU-8.

[Oztrich Boy]

Less mechanically complex, but not more efficient.

Helical propwash runs over every part of the surface. With Contra props air is kicked one way, then back and emerges (relatively) straight along the axis