Counter rotating propellers

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

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?

Several: Main one was that the torque effects cancelled out, so that
the aeroplane wasn't always trying to turn itself over/around in flight,
which was getting to be a real pain even with the last generation of
WW fighters, let alone the more powerful ones coming along. I've spoken
to at least one pilot who flew Seafires (the carrier-based Spitfire
derivative) and he was lavish in his praise of the F.47 which used
contraprops - "it flew like a jet" - less so of the earlier
Griffon-engined types. And the Seafires "only" had 2200hp or so - imagine
what the torque effects would have been in something like the Westland
Wyvern (3600hp) without contraprops (and it was no delight with 'em).
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. Go to contraprops (as on
the Avro Shackleton) and you had four identical engines and the torques
cancelling out.

Another issue was ground clearance - by the generation of fighters which
included the Corsair and its peers it was getting /very/ difficult to
put a big enough prop on the front to handle the power. Contraprops
cut down the size of the prop disc and made for easier takeoffs and
landings (the undercarriage didn't need to be so nose-up).

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.

Except that (almost - the Harvard is the exception I can think of)
pretty well all aeroplanes already used geared engines (and had since
rotaries went out of fashion in 1918 or so) - so you already had the
gearbox there.

Another issue is that it makes it easier to combine more than one engine
on one shaft (the fewer shafts the better for aerodynamics, but you might
not want a single enormous engine turning over for cruise, say). The
Fairey Gannet did this - two turboprops driving a contraprop. For takeoff
or speed you ran both engines, for stooging around (the Gannet did ASW
and AEW) you ran on one engine.

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.

Chack out the engine powers! The turboprops on the Bear are /big/ -
14000+shp, IIRC. There's no way you could fit in propellors big enough
to take that power and have an aeroplane which could be handled on the
ground - even with the contraprops the airliner derivative (Tu114)
wouldn't fit into normal airport gates..

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?

Not sure whether the Antonev 70 is actually in production yet, but it uses
four big contraprops..

--
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)

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?

--
"It's easier to find people online who openly support the KKK than
people who openly support the RIAA" -- comment on Wikipedia
(Email: zen19725 at zen dot co dot uk)

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

Andy,



ANDREW ROBERT BREEN wrote:
In article ,
Raoul wrote:

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

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?

Great reply.................

Major snip...................

Not sure whether the Antonev 70 is actually in production yet, but it uses
four big contraprops..


IIRC, the An-70 is not a contraprop as such - the D-27 engine is a
twin-spool propfan - and the props are driven by the two shafts, not
through a 'normal' contraprop gearbox.

It has 8 blades in the front row and 6 in the rear - 14 blades per
engine - making a staggering total of 56 blades !!!

It is extremely fuel efficient.........

Ken

"Ken Duffey" wrote in message
...
Andy,



ANDREW ROBERT BREEN wrote:
In article ,
Raoul wrote:

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

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?

Great reply.................

Major snip...................

Not sure whether the Antonev 70 is actually in production yet, but it
uses
four big contraprops..


IIRC, the An-70 is not a contraprop as such - the D-27 engine is a
twin-spool propfan - and the props are driven by the two shafts, not
through a 'normal' contraprop gearbox.

It has 8 blades in the front row and 6 in the rear - 14 blades per
engine - making a staggering total of 56 blades !!!

It is extremely fuel efficient.........

Wait a sec. If this was such an extremely fuel efficient system, the
short-haul airlines would be banging down the various manufacturers' dorrs
demanding such systems--which they decidedly ain't doing. The prop fan
configuration was tested here in the US a few years back (on a DC-9
airframe, IIRC), and it apparently was found wanting (how much of a problem
in that regard the noise issue is I don't know). The An-70 has had a rather
troubled development history (so much so that the Russians have gotten
rather cold to it), and IIRC one of the major problems has been the
powerplant.

Brooks


Ken

Raoul wrote:

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?


Contraprops allow large amounts of shaft-horsepower to be turned into
thrust without making a single-engined aircraft unhandlable through
torque effects. At takeoff, full throttle can be applied with no
unbalanced effect on the aircraft. The extra number of blades also
allows the diameter to be reduced, helping to keep the ends off the
ground and tip speeds lower. They aren't seen today because nobody is
trying to put that much power through propellors.

Peter Stickney gave me some very good answers to a similar question a
little while ago. Here is an extract from our conversation:

------------------------

Peter Stickney wrote:
In article ,
Alan Dicey writes:
Peter Stickney wrote:

iii) How does this work with contraprops? On the face of it they
must interfere with each other horribly, but they seem to fly
quite well.

What you gain is a greater ability for a propeller of a particular
diameter to absorb power, adn the elimination of torque and
P-factor (destabilization of the airframe due to the rotating
airflow from the propeller affecting the airframe).

So, for an increase in power turned into thrust there's an
improvement in flyability and the ability to make the airframe
lighter because it doesn't have to absorb the stresses - they're
balanced out at the source. That explains to me how the Fairey
Gannet was able to shut off one half of the Double Mamba powerplant,
feather one half of the contraprop and achieve better endurance at
patrol speed.

Right. Another example would be the Griffon engined Seafires. With a
single rotation prop, the Griffon Seafires had 5-bladed single
rotation propellers, and were limited to roughly 66% power on takeoff.
This was because of 2 reasons - the Torque/P-Factor would drag the
airplane right into the carrier's island. (A bad idea), and trying to
hold it straight was overstressing the tire sidewalls, forcing tire
changes after only a couple of flights. It's tough when you've got to
explain that you need to pull your ship out of the battle because you
ran out of tires, rather than gas, bullets, or bombs. The contraprop
used on the later Seafire 47s (6 blades, 3 per bank) allowed more
power to be used without the swing, and better propeller clearance.

The same basic engine allowed the development of the Avro Lincoln into
the Shackleton - you could hang Griffons with contraprops in the same
wing center section without changing the location of the engine
mounts. That's basically a Lancaster wing, so they got a lot of
stretch out of it.

In article ,
Raoul writes:
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?

Other folks have been covering aspects of this well, so I'll leave out
the long treatise.
There's one things that is being messed. Since a contraprop allows
more power to be absorbed by a smaller siameter propeller, the tip
speed of the propeller is lower. This is important, since teh
efficiency of the propeller drops sharply as teh flow over the
propeller goes transonic and supersonic. Since the propeller tip
speed is the vector sum of teh propeller's rotational speed adn its
forward airspeed, it allows better overall efficiency at higher
speeds.
The Tu-95 uses this in two ways. Not only does the contraprop cut
down on the propeller diameter, but the props are geared to turn at
about 760 RPM. This allows that big meatgrinder to churn along at
Mach 0.85. (Which allows it to outpace a Tornado in dry (No reheat)
thrust.)

--
Pete Stickney
A strong conviction that something must be done is the parent of many
bad measures. -- Daniel Webster

"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?

There's not many engines you could do that with considering
the fittings for the accessory drives and power connections
tend to make the ends different. Then there are the stress loads,
were WWII aircraft engines structural?
I'm sure you could design an engine you *could* do it with
but it's most likely going to be a good bit heavier.