boacvc10
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Engine Fan Spin Direction Question

Sun Jul 26, 2009 8:43 pm

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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DocLightning
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RE: Engine Fan Spin Direction Question

Sun Jul 26, 2009 9:09 pm

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.
-Doc Lightning-

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timz
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RE: Rotor Spin Direction

Sun Jul 26, 2009 9:16 pm



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

By "tandem" you mean like a Chinook or Piasecki?
 
FredT
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RE: Engine Fan Spin Direction Question

Sun Jul 26, 2009 9:26 pm

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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B727LVR
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RE: Engine Fan Spin Direction Question

Sun Jul 26, 2009 9:32 pm



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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KELPkid
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RE: Engine Fan Spin Direction Question

Sun Jul 26, 2009 9:40 pm



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...
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timz
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RE: Spin Direction

Sun Jul 26, 2009 9:57 pm

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?
 
FredT
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RE: Engine Fan Spin Direction Question

Sun Jul 26, 2009 10:33 pm

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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474218
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RE: Engine Fan Spin Direction Question

Sun Jul 26, 2009 10:37 pm

If the engines on each wing rotated in an opposite direction you would need twice the number of spare engines and parts.
 
timz
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RE: Engine Fan Spin Direction Question

Sun Jul 26, 2009 11:06 pm

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?
 
Mir
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RE: Engine Fan Spin Direction Question

Sun Jul 26, 2009 11:45 pm



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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timz
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RE: Engine Fan Spin Direction Question

Sun Jul 26, 2009 11:49 pm

How about the J41, or whatever other c/r turboprops exist? (Are there any other c/r turboprops, aside from the OV-10?)
 
Viscount724
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RE: Engine Fan Spin Direction Question

Sun Jul 26, 2009 11:57 pm

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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thegeek
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RE: Engine Fan Spin Direction Question

Mon Jul 27, 2009 12:01 am

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.
 
tdscanuck
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RE: Engine Fan Spin Direction Question

Mon Jul 27, 2009 2:43 am



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.
 
timz
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RE: Engine Fan Spin Direction Question

Mon Jul 27, 2009 2:46 am



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.
 
MrChips
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RE: Engine Fan Spin Direction Question

Mon Jul 27, 2009 5:13 am



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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KELPkid
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RE: Engine Fan Spin Direction Question

Mon Jul 27, 2009 5:19 am



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...
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FredT
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RE: Engine Fan Spin Direction Question

Mon Jul 27, 2009 6:30 am



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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thegeek
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RE: Engine Fan Spin Direction Question

Mon Jul 27, 2009 7:17 am



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.
 
Mir
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RE: Engine Fan Spin Direction Question

Mon Jul 27, 2009 9:38 am



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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Faro
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RE: Engine Fan Spin Direction Question

Mon Jul 27, 2009 10:34 am

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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boacvc10
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RE: Engine Fan Spin Direction Question

Mon Jul 27, 2009 12:38 pm



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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rwessel
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RE: Engine Fan Spin Direction Question

Mon Jul 27, 2009 11:48 pm



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).
 
tdscanuck
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RE: Engine Fan Spin Direction Question

Tue Jul 28, 2009 5:25 am



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.
 
DH106
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RE: Engine Fan Spin Direction Question

Tue Jul 28, 2009 8:30 am



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).

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 by the fixed stator blades 'straightening' the airflow have an overall torque effect ? Perhaps the turbine section counters the compressor / fan section - but it seems to me the torque generated would be in the same direction since the complete rotor turns in one direction ?
I think some of the larger multi-spool engines have contra-rotating spools, which would effectively cancel out ?
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CosmicCruiser
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RE: Engine Fan Spin Direction Question

Tue Jul 28, 2009 1:24 pm



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

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 were critical as they rotated inward.


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tdscanuck
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RE: Engine Fan Spin Direction Question

Tue Jul 28, 2009 3:03 pm



Quoting DH106 (Reply 25):
The rotor assemblies are very low friction so little torque is transfered to the engine case from these, but doesn't the torque created by the fixed stator blades 'straightening' the airflow have an overall torque effect ? Perhaps the turbine section counters the compressor / fan section - but it seems to me the torque generated would be in the same direction since the complete rotor turns in one direction ?

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 driveshaft, but that's not huge.

The major source of torque is force on the stator blades, but that's in opposite direction for the compressor and turbine stators so it all cancels out in the end.

The simple test is to look at swirl in the exiting flow. If the air imparted a net torque to the engine, then the engine would impart a net torque to the air. That would cause swirl. Since the air isn't swirling (in a significant way), there can't be a net torque on the engine.

You could still get orque via driveshafts (this is how helicopters transmit torque from the rotor to the airframe), but on a jet engine this is very small compared to the overall power in the engine.

Quoting DH106 (Reply 25):
I think some of the larger multi-spool engines have contra-rotating spools, which would effectively cancel out ?

It helps cancel out swirl in some spots, but since the rotor can't transmit (much) torque to the airframe anyway, I'm not sure it makes a difference.

Tom.
 
KELPkid
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RE: Engine Fan Spin Direction Question

Tue Jul 28, 2009 3:31 pm



Quoting CosmicCruiser (Reply 26):

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

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 were critical as they rotated inward.

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). The V-1750 was originally designed to a US Navy specification as an airship engine which was fully reversible in flight...(via a gearbox)  Wink
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474218
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RE: Engine Fan Spin Direction Question

Tue Jul 28, 2009 4:40 pm

.

Quoting KELPkid (Reply 28):
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). The V-1750 was originally designed to a US Navy specification as an airship engine which was fully reversible in flight...(via a gearbox)

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 reverse direction and kept the firing order the same. The gearbox and the accessories could be mounted on either end of the crank.
 
DH106
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RE: Engine Fan Spin Direction Question

Tue Jul 28, 2009 9:11 pm



Quoting Tdscanuck (Reply 27):
Quoting DH106 (Reply 25):
I think some of the larger multi-spool engines have contra-rotating spools, which would effectively cancel out ?

It helps cancel out swirl in some spots, but since the rotor can't transmit (much) torque to the airframe anyway, I'm not sure it makes a difference.

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 stators would create opposing and canceling torque. Obviously irrelevant since - as you've said - the turbines cancel the compressors.
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rwessel
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RE: Engine Fan Spin Direction Question

Tue Jul 28, 2009 10:59 pm



Quoting CosmicCruiser (Reply 26):
The P-38 had counter-rotating engines. Little did they know then, because they rotated outward, both were critical.

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 platform (which apparently was a bigger issue than single engine takeoff performance). The prototype had inwardly rotating props, but they changed on the production models.
 
CosmicCruiser
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RE: Engine Fan Spin Direction Question

Tue Jul 28, 2009 11:05 pm



Quoting Rwessel (Reply 31):
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 platform (which apparently was a bigger issue than single engine takeoff performance).

I didn't know that..but it does make since. thx
 
timz
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RE: Engine Fan Spin Direction Question

Tue Jul 28, 2009 11:59 pm

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 engines all rotate the same way?
 
KELPkid
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RE: Engine Fan Spin Direction Question

Wed Jul 29, 2009 12:14 am



Quoting Timz (Reply 33):

So the V-1710s on the P-38 themselves counter-rotated? Not just the props?

See 474218's response above  Wink Basically, on the left-hand rotating engine, the crank was installed "backwards," the reduction gearbox was attached to the back of the engine block instead of the front, and then the whole engine assembly on that side of the aircraft was installed "backwards"  spin  A very simple way to avoid "handed" components on a piston engine  Smile
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afterburner
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RE: Engine Fan Spin Direction Question

Wed Jul 29, 2009 12:37 am



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

or a V-22 Osprey?  Smile

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