One bladed propeller

[David J. Gall]

...a coarser pitch in climb and a finer pitch in cruise....

Of course, we all recognize that you meant "a finer pitch in climb and a coarser pitch in cruise." Thanks for the great link!

[cluttonfred]

Of course, we all recognize that you meant "a finer pitch in climb and a coarser pitch in cruise." Thanks for the great link!

Yup, what he said.

[Bill Berson]

A one blade prop can be mass balanced, but not aerodynamically balanced. I suppose the centrifugal force tends to counteract the aero imbalance some.
One bladed helicopters have flown. Not so good for helicopters, I think.