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Engine Fan Spin Direction Question  
User currently offlineBoacvc10 From United States of America, joined Jul 2006, 615 posts, RR: 0
Posted (5 years 2 months 4 weeks 5 hours ago) and read 8036 times:

What is the most common method by which the torque generated by all the engines spinning in the same direction (prop, jet) is countered ? Is it not more advantage to have left-hand spin countering right-hand spin for different engines (on different sides) ?


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35 replies: All unread, showing first 25:
 
User currently offlineDocLightning From United States of America, joined Nov 2005, 19927 posts, RR: 59
Reply 1, posted (5 years 2 months 4 weeks 4 hours ago) and read 8027 times:

I believe all engines of a given type co-rotate. This is because to have a counter-rotating engine, you would have to re-engineer the whole thing in mirror image, which is not quite as straightforward as it might sound.

So both engines on an aircraft will rotate in the same direction, although I am sure there have been exceptions in history.

BTW, tandem helicopters DO have counter-rotating rotors because they would not be flyable otherwise.


User currently offlineTimz From United States of America, joined Sep 1999, 6867 posts, RR: 7
Reply 2, posted (5 years 2 months 4 weeks 4 hours ago) and read 8021 times:



Quoting DocLightning (Reply 1):
tandem helicopters DO have counter-rotating rotors

By "tandem" you mean like a Chinook or Piasecki?


User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 3, posted (5 years 2 months 4 weeks 4 hours ago) and read 8021 times:

There have been exceptions, but I can't think of any post-WWII examples of counterrotating engines.

Having handed engines creates a logistics nightmare, forcing you to stock handed versions of pretty much every part in the engines. It's just not worth it.



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User currently offlineB727LVR From United States of America, joined Jul 2008, 630 posts, RR: 0
Reply 4, posted (5 years 2 months 4 weeks 4 hours ago) and read 8012 times:



Quoting Timz (Reply 2):
By "tandem" you mean like a Chinook or Piasecki?

That correct. If both sets of blades rotated in the same direction, the torque would be ridiculus. Besides andony who would want to fly something that has to beat the air into submission is ... Well...  Wink



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User currently offlineKELPkid From United States of America, joined Nov 2005, 6407 posts, RR: 3
Reply 5, posted (5 years 2 months 4 weeks 4 hours ago) and read 8011 times:



Quoting B727LVR (Reply 4):
Besides andony who would want to fly something that has to beat the air into submission is ... Well...

I'll try and put this one in perspective a little. I got my last rating at a combined fixed-wing and rotorcraft flight school. There were several crotch rocket type motorcycles in the parking lot on any given day. Those mostly belonged to the whirlybird pilots. Also, you had to walk through an outdoor smoking area to get to the pilot's lounge and the dispatch office  yuck  . Once again, mostly the whirlybird guys out there taking a puff...  Wink I think the point is that they are no strangers to danger and exceptional risk taking...



Celebrating the birth of KELPkidJR on August 5, 2009 :-)
User currently offlineTimz From United States of America, joined Sep 1999, 6867 posts, RR: 7
Reply 6, posted (5 years 2 months 4 weeks 4 hours ago) and read 8004 times:

As for a "tandem" helicopter-- the rotors on a Chinook do rotate the same way, don't they?

Quoting FredT (Reply 3):
but I can't think of any post-WWII examples of counterrotating engines.

Jet engines, you mean?


User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 7, posted (5 years 2 months 4 weeks 3 hours ago) and read 7986 times:

Quoting Timz (Reply 6):
the rotors on a Chinook do rotate the same way, don't they?

If they did, they'd both add torque trying to yaw the helicopter in the same direction. You'd have to waste lift tilting the rotors sideways to counter this torque.

Edit: Not to mention that having both rotors spin the same way would create a lot of noise and pieces of blades. The rotors are intermeshed with each other.  Wink

Quoting Timz (Reply 6):
Jet engines, you mean?

Why would I mean jet engines? Without quite understanding what you are asking, or perhaps rather why you are asking, the answer has to be 'no, I did not mean jet engines'.

Cheers,
/Fred

[Edited 2009-07-26 15:46:23]


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User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 8, posted (5 years 2 months 4 weeks 3 hours ago) and read 7986 times:

If the engines on each wing rotated in an opposite direction you would need twice the number of spare engines and parts.

User currently offlineTimz From United States of America, joined Sep 1999, 6867 posts, RR: 7
Reply 9, posted (5 years 2 months 4 weeks 3 hours ago) and read 7967 times:

So-- the twin-engine aircraft on which the props counter-rotate all use gearing to "reverse" the prop on one wing? The engines themselves turn the same way?

User currently offlineMir From United States of America, joined Jan 2004, 21677 posts, RR: 55
Reply 10, posted (5 years 2 months 4 weeks 2 hours ago) and read 7950 times:



Quoting DocLightning (Reply 1):
So both engines on an aircraft will rotate in the same direction, although I am sure there have been exceptions in history.

Many light twins have counter-rotating props, because it makes dealing with engine-out situations easier. Even after you take into account the extra hassle for the engine manufacturer, it's worth it.

I don't know of any jet with counter-rotating engines, though.

Quoting Timz (Reply 9):
So-- the twin-engine aircraft on which the props counter-rotate all use gearing to "reverse" the prop on one wing? The engines themselves turn the same way?

The engines themselves turn the other way. The gearing would be too heavy.

-Mir



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User currently offlineTimz From United States of America, joined Sep 1999, 6867 posts, RR: 7
Reply 11, posted (5 years 2 months 4 weeks 2 hours ago) and read 7946 times:

How about the J41, or whatever other c/r turboprops exist? (Are there any other c/r turboprops, aside from the OV-10?)

User currently onlineViscount724 From Switzerland, joined Oct 2006, 25626 posts, RR: 22
Reply 12, posted (5 years 2 months 4 weeks 2 hours ago) and read 7942 times:

The problematic Airbus A400M military transport has counter-rotating props, and each prop on the same wing also rotates in opposite directions. Note directions of propeller blades on outboard and inboard engine pairs below.


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User currently offlineThegeek From Australia, joined Nov 2007, 2638 posts, RR: 0
Reply 13, posted (5 years 2 months 4 weeks 2 hours ago) and read 7940 times:

I'm pretty sure that the A400M has inboard and outboard props spinning in opposite directions, although I'm not sure if this is achieved with gearbox differences, or whole of engine differences.

User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 14, posted (5 years 2 months 3 weeks 6 days 23 hours ago) and read 7885 times:



Quoting Boacvc10 (Thread starter):
What is the most common method by which the torque generated by all the engines spinning in the same direction (prop, jet) is countered ?

For a jet it's not an issue, there's essentially zero torque to the airframe (there's essentially no swirl in the exiting flow).

Quoting Thegeek (Reply 13):
I'm pretty sure that the A400M has inboard and outboard props spinning in opposite directions, although I'm not sure if this is achieved with gearbox differences, or whole of engine differences.

Different gearboxes.

Tom.


User currently offlineTimz From United States of America, joined Sep 1999, 6867 posts, RR: 7
Reply 15, posted (5 years 2 months 3 weeks 6 days 23 hours ago) and read 7884 times:



Quoting Viscount724 (Reply 12):
each prop on the same wing also rotates in opposite directions.

Yeah, I forgot about the Breguet 941, which did the same-- but still no idea whether the engines themselves counter-rotated.


User currently offlineMrChips From Canada, joined Mar 2005, 936 posts, RR: 0
Reply 16, posted (5 years 2 months 3 weeks 6 days 20 hours ago) and read 7849 times:



Quoting FredT (Reply 3):
There have been exceptions, but I can't think of any post-WWII examples of counterrotating engines.

Nearly every model of light piston twin made by Piper use counter-rotating engines - the only exceptions are the Aztec and the Aerostar (which isn't really a Piper, after all). Interestingly, the Piper Cheyenne 400/400LS twin turboprop also uses counter-rotating propellers, unlike the rest of the Cheyenne series, which use same-handed props.



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User currently offlineKELPkid From United States of America, joined Nov 2005, 6407 posts, RR: 3
Reply 17, posted (5 years 2 months 3 weeks 6 days 20 hours ago) and read 7848 times:



Quoting Tdscanuck (Reply 14):


For a jet it's not an issue, there's essentially zero torque to the airframe (there's essentially no swirl in the exiting flow).

Yeah, but are there not rotating mass/gyroscopic issues? After all, a jet engine (especially in a widebody) has a not so insignificant amount of rotating mass...



Celebrating the birth of KELPkidJR on August 5, 2009 :-)
User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 18, posted (5 years 2 months 3 weeks 6 days 19 hours ago) and read 7829 times:



Quoting Mir (Reply 10):
The engines themselves turn the other way. The gearing would be too heavy.

The weight could be dealt with. After all, there's plenty of reduction gearing around and if you have that, reversing the direction wouldn't necessarily add much weight.

Quoting Viscount724 (Reply 12):
The problematic Airbus A400M military transport has counter-rotating props



Quoting MrChips (Reply 16):
Nearly every model of light piston twin made by Piper use counter-rotating engines

Obviously I'd missed those. Thank you for pointing them out, I stand corrected! Live and learn.  Smile

Cheers,
/Fred



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User currently offlineThegeek From Australia, joined Nov 2007, 2638 posts, RR: 0
Reply 19, posted (5 years 2 months 3 weeks 6 days 18 hours ago) and read 7812 times:



Quoting FredT (Reply 18):
The weight could be dealt with. After all, there's plenty of reduction gearing around and if you have that, reversing the direction wouldn't necessarily add much weight.

Does this apply to piston powered props though? A Google search tells me that it applies to some, but not the majority. It shouldn't be too hard to reverse the direction of a piston engine. Firing order and camshaft profile (if asymetric on opening & closing) are the main issues I can think of.


User currently offlineMir From United States of America, joined Jan 2004, 21677 posts, RR: 55
Reply 20, posted (5 years 2 months 3 weeks 6 days 16 hours ago) and read 7777 times:



Quoting FredT (Reply 18):
The weight could be dealt with. After all, there's plenty of reduction gearing around and if you have that, reversing the direction wouldn't necessarily add much weight.

It could be, but every little bit counts on a light twin, and it's not that hard to build a piston engine that turns the other way.

-Mir



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User currently offlineFaro From Egypt, joined Aug 2007, 1556 posts, RR: 0
Reply 21, posted (5 years 2 months 3 weeks 6 days 15 hours ago) and read 7765 times:

Quoting Tdscanuck (Reply 14):
Quoting Boacvc10 (Thread starter):
What is the most common method by which the torque generated by all the engines spinning in the same direction (prop, jet) is countered ?

For a jet it's not an issue, there's essentially zero torque to the airframe (there's essentially no swirl in the exiting flow).

Maybe near-to-zero thrust-induced torque but what about precession effects of the rotating engine assemblies? Those must be considerable for big fans like the GE90. Would they be noticeable, ie is there a tangible difference in handling between a 777 at full thrust and a Gimli version of the same?

Faro

[Edited 2009-07-27 03:38:20]


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User currently offlineBOACVC10 From United States of America, joined Jul 2006, 615 posts, RR: 0
Reply 22, posted (5 years 2 months 3 weeks 6 days 13 hours ago) and read 7715 times:



Quoting KELPkid (Reply 17):

Quoting Tdscanuck (Reply 14):


For a jet it's not an issue, there's essentially zero torque to the airframe (there's essentially no swirl in the exiting flow).

Yeah, but are there not rotating mass/gyroscopic issues? After all, a jet engine (especially in a widebody) has a not so insignificant amount of rotating mass...

Ok, if the fan blade spin direction is not directly affecting a jet engine performance, then are engines typically (for civil airliners) equipped with variable diameter or variable shaped exhaust outlets ? What about any thrust vectoring mechanisms - apart from the use of a thrust reverser?



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User currently offlineRwessel From United States of America, joined Jan 2007, 2368 posts, RR: 2
Reply 23, posted (5 years 2 months 3 weeks 6 days 2 hours ago) and read 7555 times:
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Quoting Thegeek (Reply 19):
Does this apply to piston powered props though? A Google search tells me that it applies to some, but not the majority. It shouldn't be too hard to reverse the direction of a piston engine. Firing order and camshaft profile (if asymetric on opening & closing) are the main issues I can think of.

If a piston engine is designed to be reversed, it can be a matter of a few parts that distinguish a right and left handed engine. For a flat or inline engine, possibly as little as a different camshaft and perhaps a timing gear on the magneto. You may need to futz with the accessory drive as well (or rig the accessories to run off the wrong rotation).

But you shouldn't overlook the easiest way to make a piston engine run in reverse - mount it backwards. That does require access to the crankshaft at both ends of the engine, and you will have to figure out what to do with the accessories (run them off a reverse drive at the front of the engine, or run the in the normal direction at the back).


User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 24, posted (5 years 2 months 3 weeks 5 days 20 hours ago) and read 7493 times:



Quoting Faro (Reply 21):
Maybe near-to-zero thrust-induced torque but what about precession effects of the rotating engine assemblies? Those must be considerable for big fans like the GE90. Would they be noticeable, ie is there a tangible difference in handling between a 777 at full thrust and a Gimli version of the same?



Quoting KELPkid (Reply 17):
Yeah, but are there not rotating mass/gyroscopic issues?

Yes, but those only show up when you try to change the angular momentum of the engine quickly. Commercial airliners can't achieve very large pitch or yaw rates for any length of time, and roll doesn't change the angular momentum of the engines. These concerns drive many load cases for the pylons and engine mounts, but aren't a huge factor for the airplane because the gyro torque of the engines still isn't that large relative to the airplane's inertia.

One of the more significant cases is the locked rotor situation, where all the angular momentum of the core is suddenly imparted to the pylon. But, even then, it's more of a structural issue than a control one.

Quoting BOACVC10 (Reply 22):
Ok, if the fan blade spin direction is not directly affecting a jet engine performance, then are engines typically (for civil airliners) equipped with variable diameter or variable shaped exhaust outlets ? What about any thrust vectoring mechanisms - apart from the use of a thrust reverser?

No. It's definitely not typical (not counting thrust reversers). Off the top of my head, I can't think of any current production commercial engine that has these features, but I'm sure someone knows of a corner case. Concorde would have had this to accommodate the afterburners, but nobody's building those engines now.

Tom.


25 DH106 : Interesting. The rotor assemblies are very low friction so little torque is transfered to the engine case from these, but doesn't the torque created
26 CosmicCruiser : The P-38 had counter-rotating engines. Little did they know then, because they rotated o outward, both were critical. The Navajo did too; neither wer
27 Tdscanuck : You're right that the rotor can't transmit any torque to the engine because of the bearings. Some torque comes out through the auxiliary gearbox driv
28 KELPkid : IIRC, the Allison V-1750's in the P-38 were reversed using a gearbox (also present even on the "turning the natural way" engine for gear reduction).
29 474218 : . The Allison V-1750 used by the P-38's could have their crankshaft installed in either direction. By reversing the crank the engine could turn in the
30 DH106 : Thanks for the info Tom - the 'lack of swirl' explanation makes sense. The point I meant by the contra-rotating spools was that their respective stat
31 Rwessel : Actually they did know. The outward rotation apparently reduced the disturbed airflow over the tail, and made the P-38 a better, more stable, gun pla
32 CosmicCruiser : I didn't know that..but it does make since. thx
33 Timz : So the V-1710s on the P-38 themselves counter-rotated? Not just the props? How about the Hornet? But on the few turboprops with handed props, the engi
34 KELPkid : See 474218's response above Basically, on the left-hand rotating engine, the crank was installed "backwards," the reduction gearbox was attached to t
35 Afterburner : or a V-22 Osprey?
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