Contra-Rotating Props in WWII

ACResearcher

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While many U.S. combat aircraft in WWII were intended to have contra-rotating props, the U.S. never seems to have successfully developed a usable contra-rotating propeller system.

Why is this? What were the failings of the systems created and tested? How did the successful systems developed by the British differ from those created by U.S. manufacturers?

AlanG
 

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ACResearcher said:
While many U.S. combat aircraft in WWII were intended to have contra-rotating props, the U.S. never seems to have successfully developed a usable contra-rotating propeller system.


Really? Which aircraft were intended to have contras?
 
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CostasTT

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The Republic XP-72 (second prototype) is the first that comes to mind. Then there is also the Fisher P-75 Eagle and others.
 

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Northrop P-56.
Northrop%2BXP-56-Black%2BBullet%2BSecond-Prototype.jpg

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Douglas B-42.
doug_xb42_157.jpg

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Abraham Gubler

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ACResearcher said:
Why is this? What were the failings of the systems created and tested? How did the successful systems developed by the British differ from those created by U.S. manufacturers?

Not all contra rotating props are equal. Basically a contra rotating prop is a complex gearbox. What drives gearbox dynamics is power input. The UK built contra rotating props in the first half of the 1940s for engines in the 1,000 to 2,000 hp range (Merlin, Griffon). The well-known ‘failed’ American contra rotating props at this time were for much more powerful inputs in the 2,000-4,000 hps range (Wasp Major and twin V-1710s). So they were much harder to engineer with the more dramatic results.
 

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Ok, there are certainly prototypes actually fitted with contra props.


but from the original post


many U.S. combat aircraft in WWII were intended to have contra-rotating props
so presumably some in service aircraft were supposed to have them but production aircraft didnt?
 

ACResearcher

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Perhaps time for a bit more clarification!
There was a large number of aircraft that were intended/hoped to receive counter rotating props. In addition to those shown below are the XP-47B "Double Twister", XP-62 (several variants), XP-71, XP-72, XF14C, XB-35, etc. All of those that actually flew were fitted with the counter-rotating prop but it was soon swapped out for a standard 4-blade propeller.
I think Abraham may have hit upon a key feature that I had not considered - horsepower. All the above aircraft used engines in the power range of a minimum of 2000hp and upwards of 4000hp - R-2800, R-3420, R-3350 and R-4360.
This still leaves open the question of why the U.S. manufacturers were unable (or just plain didn't bother) to overcome the engineering challenges involved in perfecting the counter-rotating prop mechanisms. My first guess is that there was no point as we were rapidly moving toward jets. Still, the amount of power available to such a powerplant is certainly shown in the mighty Tu-95/142 and other Russian aircraft.
Thank you all for your hypothesizing. Keep it coming!
AlanG
 
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CostasTT

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From what I've seen, US aircraft intended to have contraprops did not go forward because of problems with the overall design of the aircraft itself (e.g. XP-56), changing requirements or inadequate performance (e.g. P-75) and of course the advent of jet power, which led to a general trend away from prop driven aircraft. Therefore, in my opinion, it's quite unfair to blame everything on the complexity necessary for the contraprop gearbox.
 
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joncarrfarrelly

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Evidently the system used on the XB-42 worked fine:


[font=.HelveticaNeueUI]http://www.enginehistory.org/Propellers/Curtiss/XB-42Prop.shtml[/font]
 

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Manta Contra-Rotating
 

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Abraham Gubler said:
Not all contra rotating props are equal. Basically a contra rotating prop is a complex gearbox.

Fully agree to the first point, but not to the second. The Douglas XB-42 is an example for contra-rotating
props without that gearbox, as it was driven be two engines, in the same way as the Do 335.
 

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Maybe I'm wrong, but I seem to remember that the operational UK contra-rotating aircraft were mostly or all post war. Does this mean simply that the UK stuck with high horsepower prop aircraft longer than the US? Did the US just give up on contra-props and concentrate on jets earlier than the UK?
 

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Bill Walker said:
Maybe I'm wrong, but I seem to remember that the operational UK contra-rotating aircraft were mostly or all post war. Does this mean simply that the UK stuck with high horsepower prop aircraft longer than the US? Did the US just give up on contra-props and concentrate on jets earlier than the UK?


I'd say the short answer is yes, but I'm not especially recondite on UK aircraft. In the US, contraprop development largely co-evolved with the Hyper engines, and went extinct with them. BTW, I'm reading Kim McCutcheon's Chrysler Aircraft Engines, and, he reveals that, in addition to the millions they spent on their inverted V-16, they developed and patented a contraprop design specifically geared to its unique crankshaft layout.
 

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Bill Walker said:
Maybe I'm wrong, but I seem to remember that the operational UK contra-rotating aircraft were mostly or all post war. Does this mean simply that the UK stuck with high horsepower prop aircraft longer than the US? Did the US just give up on contra-props and concentrate on jets earlier than the UK?


Not exactly. The US kept working on high power contra props into the 1950s just as the British did, the A2D Skyshark for example first flew in only 1950. Early jets had poor takeoff performance which made prop driven aircraft appealing for carrier launch attack roles, otherwise jets would have surely killed them off out of hand. The problem is the US engine behind this effort, the T40 turboshaft, was never reliable and its failure forced an end to the Skyshark and several other programs. By the point it was a known failure it made no sense to start over again from scratch because of higher power jet engines appearing, with afterburners not far away, solving the takeoff issues. Also carrier catapults improved radically with the introduction of steam cats.

As it was the Skyraider far outlasted any British frontline prop driven attack or fighter plane in service, but it simply didn't need a contraprop. You really only needed those when you went past the 3000hp mark and shear engine torque began to create serious handling problems. The US never put the highest power versions of the R-4360 onto a single engine aircraft that I can think, so it didn't meet this issue with anything but the T40 engine. Earlier lower power contraprop designs were unnecessarily complicated.
 

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Did the YB-35 have Contra rotating props?. I came across this CGI illustration at:
http://emigepa.deviantart.com/art/Northrop-XB-35-flying-wing-291087123
That indicates contra props as does the photograph from:
http://1000aircraftphotos.com/Contributions/Hubbard/5282.htm
 

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Apteryx

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Zeppelin said:
Did the YB-35 have Contra rotating props?


Indeed it did, but the extension shafts vibrated and the gearboxes gave trouble. Eventually the YB-35 was fitted with four-bladed single-rotation props.
 

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It is interesting that US contra rotating propeller gear boxes never worked satisfactorily. Curtiss Wright had a lot of different patents on contra rotating propellers during the 1940s (see google patents) but this did not result in any hardware worth mentioning. The Allison T40 (of course post WW2) which was mentioned above consisted of two hot sections and was never trouble free. British contra rotating gearboxes were in regular operation in Spitfires, Seafires, Shackletons (all RR Griffon), Wyverns (AS Python) and Gannets (AS Duoble Mamba). The Russians gearbox for the Kuznetsov NK-12 was constructed by German / Austrian engineers and were a development of the Stoeckicht planetary gearbox. These gears seemed to work fine. Sorry for being a little bit off-topic. Besides this would better fit into the propulsion section ;)


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Basil said:
It is interesting that US contra rotating propeller gear boxes never worked satisfactorily. Curtiss Wright had a lot of different patents on contra rotating propellers during the 1940s (see google patents) but this did not result in any hardware worth mentioning...

I could be persuaded that US firms couldn't figure out contraprops, but I'd need to see more evidence. Curtiss fitted them to the XP-60C, XP-62 and XF14C fighters, and while a prop failure may have wrecked the first of these (not sure), Curtiss felt good enough about the design to use it on the second and third types. US contraprops weren't going to develop ahead of the monster piston engines they were being prepared for, and those engines were either abandoned in 1944 or ultimately used in multiengine planes where torque and prop diameter weren't so critical.
 

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Apteryx, of course US industry would have been able to build satisfying cr gerboxes if the necessary investment had been done (e g for the XT57 or the XT35) . As you said - at this time the air force was already more interested in turbojets. And the civil market shys away from complex gear boxes. They had enough to do with the R3350 single propeller engine ;)
 

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Basil said:
Apteryx, of course US industry would have been able to build satisfying cr gerboxes if the necessary investment had been done (e g for the XT57 or the XT35) . As you said - at this time the air force was already more interested in turbojets. And the civil market shys away from complex gear boxes. They had enough to do with the R3350 single propeller engine ;)


Yes, especially the Turbo-compound!
 

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Tom Fey of AEHS did some convention presentations on contra props for piston and gas turbine use. They are available for members only at their website. I suggest that you subscribe (not much) to get access to lots of useful info from people who were often involved in the work in the first place. His talk covered many engine/airframe combinations (see below). The configurations of US and UK designs is just like the Tyne and T56 turboprops we discussed elsewhere.
 

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Apteryx

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tartle said:
Tom Fey of AEHS did some convention presentations on contra props for piston and gas turbine use. They are available for members only at their website. I suggest that you subscribe (not much) to get access to lots of useful info from people who were often involved in the work in the first place. His talk covered many engine/airframe combinations (see below). The configurations of US and UK designs is just like the Tyne and T56 turboprops we discussed elsewhere.


Thanks for the tip--and, by the way, thanks for the riches you've showered on us in this forum, free of charge. :)


--Ian
 

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Abraham Gubler said:
Not all contra rotating props are equal. Basically a contra rotating prop is a complex gearbox.

Fully agree to the first point, but not to the second. The Douglas XB-42 is an example for contra-rotating
props without that gearbox, as it was driven be two engines, in the same way as the Do 335.
The XB-42, like the Brabazon and Gannet, was a coaxial installation. Two engines, each engine driving its own independently controlled propeller disk. There was a reduction gearbox in the tail of the aircraft, but the co-housed reduction systems were independent.
 

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The Hamilton Standard Superhydromatic propellers was used on the XF-11, XB-35, and Douglas XTB2D-1. It was propeller system "...designed to an ideal specification without regard to simplicity" according to Sir Roy Fedden.
 

Mark Nankivil

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The Hamilton Standard Superhydromatic propellers was used on the XF-11, XB-35, and Douglas XTB2D-1. It was propeller system "...designed to an ideal specification without regard to simplicity" according to Sir Roy Fedden.
Nice to see you on here Tom!

Enjoy the Day! Mark
 

Justo Miranda

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-Curtiss XP-60C
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ArtosStark

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As an anecdote connected to this topic, the Fairey P.24 Monarch, after being rejected by the Air Ministry, arose some interest from the USAAF. It is not entirely clear how much the engine interested them but the contra-rotating props that were an integral part of the design certainly did. The story is covered by the Old Machine Press article on the Monarch


Fairey had discussed the P.24 engine with United States Army Air Force (AAF) officials in June 1941. The following month, Forsyth visited the US to give more details about the engine. Fairey and Forsyth felt that the Air Ministry had made a mistake in exclusively backing the Napier Sabre and not providing any support for the P.24. They wanted P.24 development and production to continue in the US; production in the US by an established engine manufacturer would be easier than FAC undertaking the task themselves. By this time, the name “Monarch” was applied to the P.24 engine. In August 1941, the AAF stated that they were not interested in the development or production of the P.24 engine, but they were interested the in the contra-rotating propellers developed for the engine. However, Fairey stated in a letter dated November 1941 that Wright Field in Dayton, Ohio had prepared three-view drawings of the P.24 installed in the Republic P-47 Thunderbolt fighter and the Curtiss A-25 Shrike (SB2C Helldiver) dive bomber. Fairey also stated that the Ford Motor Company was engaged in discussions about producing the engine.

The apparent reversal of the AAF’s interest in P.24 production seems odd, and it may have been more optimism on Fairey’s part than what was really expressed by the AAF. Fairey did want to get the engine to the US, and claiming that the AAF was interested was the quickest way to get the cooperation of the Air Ministry, who had been battling Fairey for quite some time. Regardless of the AAF’s level of interest in the engine, they were certainly interested in the contra-rotating propellers. The P.24-powered Battle was shipped to the US on 5 December 1941. Another P.24 engine was delivered to Farnborough for further testing, and a third Monarch engine was prepared for shipping to the US. With the Japanese attack on Pearl Harbor, the second P.24 engine was never sent to the US.
 

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Keep in mind that the 3500hp Eagle engined Wyvern had two 4-blade contra-props so not all Brit designs were around 1000 to 2000hp. The turbine engines were to be even more powerful, 4000hp and up.
In the above I didn't see the Boeing XF8B mentioned (maybe I missed it)
 

Nicknick

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I would like to know if any airplane was equiped with something like that:


For this arrerangement you would need to put the engine in seperated nacells like in the Do28 or the Eilice aviation, which is quite unusuall with heavy piston engines. On the other hand, it might give similar advantages without having the complicated koaxial prop drive.

Please note, that the text is saying counter rotating, but the props on the picture are cleary not counter rotating...

Edit: I just remembered, the fyling boats of Dornier had that arrangement (counter rotating props in the front/back of a nacelle
 
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