Counter rotating propellers

Even by 1940, the world's air forces had discovered that there was a
problem with the more-powerful engines that were coming on line:
they'd drive the propeller too fast. Once the tips go trans-sonic, the
prop loses efficiency. So they went from two-bladed to three-bladed
props, and then to four-bladed. And they made the props longer. But
there are limits to both these solutions. Thus the notion of having
two sets of propellers, rotating in different directions.

On prop-jets these days, you routinely see multi-bladed propellers.I'm
not sure why airframe manufacturers didn't go in this direction for
warplanes, but perhaps it has to do with the power output of a plane
under combat conditions--that is, a seven-bladed prop will work on a
transport but not on a fighter. Dunno.

You're certainly right about the complexity of the counter- or
contra-rotating propellers.

all the best -- Dan Ford
email: (put Cubdriver in subject line)

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