"Orval Fairbairn" wrote

The contra-rotating props helped absorb the power of the R-4360s. Look
at the Russian Bear Bomber as another example. They also helped to
negate P-factor, as each prop had blades coming down on each side.

The contra rotating props are said to be more efficient, and it has to do
with the swirling motion props impart to the air.

When one prop hits the air, it sends it flying back at a much higher speed
which gives you thrust. It also starts the air spinning around. The energy
it takes to spin it is basically wasted, because it does not contribute to
forward thrust.

If you put another prop right behind the first prop rotating the opposite
way, the spin whacks the second prop, and takes the spin out, which converts
that spin into rearward velocity, and recovers some of the wasted energy of
the spinning prop wash.

So it is said. g
--
Jim in NC