Counter rotating propellers

(Eunometic) wrote in message . com...
Peter Twydell wrote in message ...
In article , frank may
writes
Well, counter rotating props eliminate torque on twin engined
airplanes & on at least some, improves the single engine performance &
handling. However, your question really seems to be about
contra-rotating props, which is the case of a single engine driving 2
props on a co-axial shaft, rotating opposite of each other. Same
thing, it eliminates the torque & therefore makes the airplane more
docile. Contra-rotating props are same shaft, same engine, like a late
Seafire or Shack or Bear. Counter-rotating are separate engines, like
the P-38 or F-82 or several twin engine Pipers.


Then there's the case (unique AFAIK) of the Fairey Gannet. The Double
Mamba engine is in fact two Mambas side by side, each driving one of the
two props. One half could be shut down to allow economical loiter.

As far as torque is concerned, although without a prop, don't forget the
Pegasus in the Harrier. Contra-rotating shafts to balance it so that
hovering is easier/possible.


Yes, apart from torque Gyroscopic precesion is a problem. I believe
the WW2 Me 109s nasty swing on landing and takeoff could be traced to
this prime effect with the problem worsened by the placing of the
undercarriage and the narrow track of it. Precesion is the tendancy
of a gyroscope that is spining on one axis and twisted on a second to
react by twisting on the third.

Also the turbulence of the corkscrew prop wash would effect
aerdynamics in nasty way.

AFAIKS if it weren't for the jet engine prop aircraft were heading for
pusher propellers and/or contra-rotating propellers and speeds of
540mph to 560mph.

This is the Heinker P.1076 a piston engined aircraft with a speed of
potentialy 546 mph based on refined aerodynamics, evaporative steam
cooling in the wing leading edges and contra-rotating propeller.
http://www.luft46.com/heinkel/hep1076.html

It would have been an awesome piston engined fighter opperating on
only a little more power than a Merlin.

This is the Dornier managing 514 mph on the same power:
http://www.luft46.com/dornier/dop247.html

This is a single contra rotating Dornier using two engines and a
single scimitar shaped contra-ratoating propeller to achieve a
remarkable 577 mph.
http://www.luft46.com/dornier/dop252.html

With that speed it could have outperformed most jets.

All theoretical of course but there is no reason to doubt them. The
Germans did have the world biggest wind tunnel at the end of the war
located in Austria. It could test a full sized fighter at near full
speed.