Raoul wrote in message ...


What advantages were being sought through the counter rotating
propeller and, if there were indeed advantages, why aren't they seen on
production propeller driven aircraft today?


One object of the exercise, I think, was to straighten the airflow
to get more trust from the same power. The idea is that the energy
that goes into making the air go 'round and 'round is wasted and if
the air can be pushed straight through the propulsion device then
it will be more efficient.

Two problems with counter rotating propellers a

1) The airflow into the second propellor is turbulant which impairs
the efficiency of the second propeller.

and

2) The counter-rotating propellers put energy into spinning
the air and then put more energy into 'despinning' the
air. No energy is regained by straightening the flow.

IIRC ducted fanjets do spin the outerflow counter to the inner
flow through the turbine. I don't think that improves the
efficiency, rather it reduces the net torque on the aircraft.

There have been successful designs that used seperate engines to
spin a fore and aft propeller, the DO-335, the Cessna-337 and
it's military equivalent that you seen in the movie _Bat 21_, I
forget the designation, O-something.

These use counterrotating engines so that there is no net torque
on the fuselage, which improves handling rather than efficiency.
There is an additional advantage in that putting two engines inline
allows the use of the power of another engines without the additional
drag of another nacelle. I think Rutan has a GA aircraft with a
similar configuration to the DO-335.

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FF