Counter rotating propellers

(phil hunt) wrote in message ...
On 18 Sep 2004 16:05:44 +0100, ANDREW ROBERT BREEN wrote:
A related issue was maintainance (this for multi-engine types): if you
wanted to avoid torque effects you had to have "handed" engines, turning
in different directions on each side (like the Lockheed Lightning or the
De Havilland Hornet), or you put up with the torque effects and had the
mainatainance/suppy gain of n identical engines.

Couldn't you use identical engines, but mount them back-to-front on
one wing?


Dornier made an amphibious flying boat known as the Do 26 that used
this technique. The rear engines even tilted up 13 degrees to keep
them out of the water during takeoff. It was a pretty aircraft.

Becuase the Do 26 was powered by diesels it could be refueled at any
port with diesel and it had an enormous range for a pre war aircraft
of 5500 miles.

I used to dream of taking one on a round the world trip refueling in
yacht ports as we go.

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.

--

FF

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.



Raoul wrote in message ...
I've had a questions I'd like to foist upon the collective knowledge
here...

I have a few of those "World's Worst Airplane" books and enjoy reading
about the creations of those in the old days who were basically working
by the seat of their pants.

I've noticed that their were many planes during the prop-to-jet
transition years from about 45 to about 55 that used counter rotating
propellers. I'm wondering what the perceived advantage was?

Seems to me that the added complexity and cost would be a disadvantage.
It's pretty simple with one propeller: Take engine. Fasten propeller to
flange on front. Put on airplane, Fly into the wild blue yonder, All
those gears and driveline parts were mighty complex and, in my reading,
the added complexity was usually the thing that put the plane into the
'world's worst' catagory.

I notice that notable post war military aircraft such as the B-36 and
the C-130 (plus more) used one propeller per shaft. If there were an
advantage, you'd think you'd find 'em on a military plane. Yet, if my
reading is correct, the Soviet long-range Bear bomber had
counterrotating propellers.

So, that leaves me again with my initial question:

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?

raoul

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.
--
Peter

Ying tong iddle-i po!

In article ,
Peter Twydell wrote:

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.

Unique in production, but didn't the Blackburn prototype offered for the
same spec have the same arrangement? And before that, of course, there was
the Fairey P.24 Prince engine (essentially a V12 and an inverted V12,
each driving its own proellor on the same axis) - that was trialled in
a Battle (which was said to have a fairly startling performance). It
was offered to Republic as a powerplant for the P47, but got canned
as the Min. of Supp. didn't want Fairey trying to do too many things at
once.

--
Andy Breen ~ Interplanetary Scintillation Research Group
http://users.aber.ac.uk/azb/
"Time has stopped, says the Black Lion clock
and eternity has begun" (Dylan Thomas)

In message , Peter Twydell
writes
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.

Wasn't the Gannet designed for naval officers to fly standing up?

Mike
--
M.J.Powell

In article , M. J. Powell
writes
In message , Peter Twydell
writes
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.

Wasn't the Gannet designed for naval officers to fly standing up?


It could well have been, but I bet they couldn't have done it with the
same flair as Stringbag display crews do it now: White Ensign flying and
the Observer and TAG saluting to the side.
http://www.stringbag.flyer.co.uk/rnh...es/ls326_6.jpg is the best I
can find at the moment.

--
Peter

Ying tong iddle-i po!

In message , Peter Twydell
writes
In article , M. J. Powell
writes
In message , Peter Twydell
writes
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.

Wasn't the Gannet designed for naval officers to fly standing up?


It could well have been, but I bet they couldn't have done it with the
same flair as Stringbag display crews do it now: White Ensign flying
and the Observer and TAG saluting to the side.
http://www.stringbag.flyer.co.uk/rnh...es/ls326_6.jpg is the best I
can find at the moment.

Lovely!

Mike
--
M.J.Powell

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.

There are some well researched German poposals by Heinkel
(contra-rotaing tractor) and Dornier (pusher) which would have pushed
piston engined speed on standard WW2 style V12 (jumo 213 and Daimler
Benz DB603 of about 1750 hp) to 540 mph or more. Given in "Secret
Lufwaffe Projects"

Without the jet taking over this is the speed piston engined aircaft
would have reached. They would have operformed the Jets in most areas
till 1947 at least.

(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.