timz
Posts: 6086
Joined: Fri Sep 17, 1999 7:43 am

Always Same Rotation On 2-shaft Engines?

Sun Jun 05, 2005 4:25 am

On jet engines with two or three shafts, I guess the shafts usually rotate the same direction? Have there been any exceptions?

Has anyone made three-shaft engines besides RR, and maybe their partnerships?
 
Matt72033
Posts: 1589
Joined: Sat May 14, 2005 10:03 pm

RE: Always Same Rotation On 2-shaft Engines?

Sun Jun 05, 2005 4:32 am

i was under the impression only RR made 3 spool engines......could very easily be wrong though! was it the RB211 that pioneered the 3 spool technology now found in the trent aircraft?

not sure about shaft rotation!
 
air2gxs
Posts: 1443
Joined: Mon Jun 18, 2001 1:29 pm

RE: Always Same Rotation On 2-shaft Engines?

Sun Jun 05, 2005 4:39 am

Are you talking about counter-rotating shafts? If so, the answer is no. All shafts travel in the same direction. Clock-wise for PW & GE, counter-clockwise for RR.
 
Okie
Posts: 3534
Joined: Wed Jul 16, 2003 11:30 am

RE: Always Same Rotation On 2-shaft Engines?

Sun Jun 05, 2005 4:43 am

I can not answer for all turbines but as an engineer I would say that they would be rotating the same direction due to the bearing speeds.

If one shaft was turning 5,000rpm and the other 2,000rpm then the bearing would be at 3,000rpm if rotating the same direction and 7,000 if turning the opposite direction.

Okie
 
EMBQA
Posts: 7795
Joined: Sat Oct 25, 2003 3:52 am

RE: Always Same Rotation On 2-shaft Engines?

Sun Jun 05, 2005 4:55 am

Every jet engine I have ever seen has just one shaft... Now Turbine spools is a whole new story....
"It's not the size of the dog in the fight, but the size of the fight in the dog"
 
B747FE
Posts: 217
Joined: Mon Jun 21, 2004 11:09 pm

RE: Always Same Rotation On 2-shaft Engines?

Sun Jun 05, 2005 6:11 am

The Rolls Royce Trent 900 was designed with a contra-rotating HPC/HPT module.
Check this out:

http://www.rolls-royce.com/civil_aer...ines/trent900/technology_flash.jsp

Regards,
B747FE.
"Flying is more than a sport and more than a job; flying is pure passion and desire, which fill a lifetime"
 
gigneil
Posts: 14133
Joined: Fri Nov 08, 2002 10:25 am

RE: Always Same Rotation On 2-shaft Engines?

Sun Jun 05, 2005 1:28 pm

The Trent 900 and Trent 1000 have counter-rotating high pressure spools.

If I'm not mistaken, the GEnx will also feature contra-rotation.

N
 
IFIXCF6
Posts: 107
Joined: Tue Sep 14, 2004 12:06 pm

RE: Always Same Rotation On 2-shaft Engines?

Sun Jun 05, 2005 1:53 pm

Quote:
I can not answer for all turbines but as an engineer I would say that they would be rotating the same direction due to the bearing speeds.

If one shaft was turning 5,000rpm and the other 2,000rpm then the bearing would be at 3,000rpm if rotating the same direction and 7,000 if turning the opposite direction.

This is not the way bearings are used in engines I have maintained. Specifically, I know more about CF6's than other engines. The -80C2 has 7 total bearings, with the 1B, 2R, and 6R supporting the Fan/LPT (N1). N2 (core/HPT) uses bearings 3R, 4R, 4B, and 5R. The "R" and "B" indicate roller or ball bearings. The balls are thrust bearings, hence 1 on each rotor. Why 2 #4's. No idea. But you can see the rotors (yes, one is on a spool, one is on a shaft), are supported by seperate bearings.

The case for or against counter-rotation is probably an aerodynamic efficiency question. Since stators (non-moving vanes between each set of rotating blades) are used to straighten the airflow, I think it has possibilties. However, turning the Fan/LPT in one direction, and the core/HPT in the other does not seem to be that great an improvement. What if you could alternate rotation from one stage to the next, throughout the engine? A mechanical nightmare, but what...in terms of efficiency? Could you eliminate stators, with their drag? Or just reduce their profile? I don't know. I'm just a mechanic. But these thoughts come to mind.

Mike
 
Lemurs
Posts: 1320
Joined: Sat Mar 12, 2005 5:13 am

RE: Always Same Rotation On 2-shaft Engines?

Sun Jun 05, 2005 2:39 pm

Quoting Gigneil (Reply 6):
If I'm not mistaken, the GEnx will also feature contra-rotation

You're right on. If you go to GE's press site for the GEnx and look at the flash demonstrator applet, they discuss it there. They state this allows for some of the efficiency gains in this new core, unsurprisingly.
There are 10 kinds of people in the world; those who understand binary, and those that don't.
 
Finkenwerder
Posts: 120
Joined: Sat Apr 30, 2005 4:54 am

RE: Always Same Rotation On 2-shaft Engines?

Sun Jun 05, 2005 8:16 pm

Rolls Royce did it 30 years ago with the Pegasus ............Counter rotating shafts !!

To avoid gyroscopic effects in the hover so I was told, as a fresh faced Harrier Force New Boy.

[Edited 2005-06-05 13:17:18]
 
User avatar
Jetlagged
Posts: 2562
Joined: Sun Jan 23, 2005 3:00 pm

RE: Always Same Rotation On 2-shaft Engines?

Mon Jun 06, 2005 12:12 am

Quoting IFIXCF6 (Reply 7):
Since stators (non-moving vanes between each set of rotating blades) are used to straighten the airflow,

Stators do more than simply straighten the airflow. They increase the air pressure by acting as a diffuser.

Stators aren't always stationary either. The GE CF6 and Pratt & Whitney JT9D engines use variable incidence stators for compressor stability. This is one complication the RR three spool design can avoid.
The glass isn't half empty, or half full, it's twice as big as it needs to be.
 
AvionicMech
Posts: 308
Joined: Mon Jan 24, 2005 7:28 am

RE: Always Same Rotation On 2-shaft Engines?

Mon Jun 06, 2005 12:47 am

I think IFIXCF6 probably meant that the stators don't spin like the rotors when he said that the stators don't move. I am sure if his username is IFIXCF6 that he probably knows all about VSV's etc.  Wink

[Edited 2005-06-05 17:49:49]
 
B747FE
Posts: 217
Joined: Mon Jun 21, 2004 11:09 pm

RE: Always Same Rotation On 2-shaft Engines?

Mon Jun 06, 2005 1:41 am

Quoting Jetlagged (Reply 10):
This is one complication the RR three spool design can avoid.

Actually, the RB211 feature a single stage of VIGV's at the IP compressor, improving airflow stability through the IP and HP modules during starting acceleration and T/R operation.

Regards,
B747FE.
"Flying is more than a sport and more than a job; flying is pure passion and desire, which fill a lifetime"
 
PW100Testpilot
Posts: 26
Joined: Sun Mar 27, 2005 3:37 am

RE: Always Same Rotation On 2-shaft Engines?

Mon Jun 06, 2005 5:35 am

A PW-100 (that's a turboprop, maybe not answering your question, but maybe interesting to know) has 3 shafts rotating into each other, an HP-shaft (HP impeller - HP turbine), a LP-shaft (LP impeller - LP turbine) and a PT-shaft (Power Turbine - Reduction Gear Box).
These shafts rotate in different directions, the LP-shaft CW with appr. 27000 RPM, the HP-shaft CCW with appr. 33000 RPM and the PT-shaft CW with 20.000 RPM
No info
 
MrChips
Posts: 933
Joined: Wed Mar 30, 2005 2:56 pm

RE: Always Same Rotation On 2-shaft Engines?

Mon Jun 06, 2005 7:18 am

In military applications, the PW F119 has a counter-rotating compressor...I am also assuming that the F135 version of the engine will be the same.
Time...to un-pimp...ze auto!
 
efohdee
Posts: 212
Joined: Fri Oct 29, 2004 4:52 am

RE: Always Same Rotation On 2-shaft Engines?

Mon Jun 06, 2005 11:09 am

The Textron Lycoming T55 712/714 turboshaft has contra-rotating turbines. Four total turbine stages. Two gas generator turbines drive the compressor. Two power turbines turn in the opposite direction to drive the output shaft. This is said to offset the effects of torque.
I think the Textron Lycoming T53 UH-1 Huey engine is the same, but I'm not sure. I've never torn into one.
 
caboclo
Posts: 175
Joined: Thu Nov 11, 2004 12:34 pm

RE: Always Same Rotation On 2-shaft Engines?

Mon Jun 06, 2005 1:28 pm

EMBQA, what's the difference between shafts and spools?
Freight dogs have more fun
 
PW100Testpilot
Posts: 26
Joined: Sun Mar 27, 2005 3:37 am

RE: Always Same Rotation On 2-shaft Engines?

Tue Jun 07, 2005 8:03 am

Quoting Caboclo (Reply 16):
EMBQA, what's the difference between shafts and spools?

It's the same, just two different nomenclatures.
But it could also be that a spool is a shaft including the compressor and turbine, but I'm not sure...
No info
 
User avatar
lightsaber
Crew
Posts: 11747
Joined: Wed Jan 19, 2005 10:55 pm

RE: Always Same Rotation On 2-shaft Engines?

Tue Jun 07, 2005 5:18 pm

Quoting Air2gxs (Reply 2):
All shafts travel in the same direction. Clock-wise for PW & GE, counter-clockwise for RR.

Correct. Prior engines are co-rotating. Note that the F119 and newer military Pratt are all counter rotating.

Quoting B747FE (Reply 5):
The Rolls Royce Trent 900 was designed with a contra-rotating HPC/HPT module.

The future is contra-rotating. There was a bearing "breakthrough" in the 90's that made it easier to take the higher effective RPM's a coutra-rotating design imposes while at the same time allowing a smaller package (needed to make a contra-rotating possible, parts have to fit...). (e.g., low spool at 1300, high spool at 12,500 creates an effective RPM of 1300+12,500 or 13,800 RPM.) A double spool gets a free 2% drop in TSFC. A tripple spool (RR) gets a free 3% drop in TSFC.

Since I worked for Pratt for over 4 years, I hope you all don't mind me going into a LOT more detail on contra-rotating engines. I really believe, now that the bearings aren't a big issue, that all future engines that aren't derivatives of exiting designs will be contra rotating.

If you know how a compressor (or turbine) works, there are alternating rotating airfoils (blades) and stationary (as in non-rotating) airfoils (stators). The stators need to take out the rotational inertia that the spool imparts on the gas path. (Note, there is diffusion going on, but I'm going to simplify.) There is a loss associated with this. Also, there is that rotational velocity that has energy. By not taking direct advantage of that energy to compress the gas (or extract work in a turbine), there are unavoidable losses. In a contra rotating design, you can match the airfoils so that at the switch between the contra-rotating spools there is no need for a stator at certain design points. This dramatically improves efficiency.

Now Pratt will always put in a stator between the contra-rotating spools. Why? Better efficiency off of the design point. However, this lengthens the engine hitting the design with a weight penalties. In the F119 vs. F120 competition for the F-22, the Pratt engine won mostly due to improved fuel economy off of full power. Why? GE likes to take out the stator between contra rotating stages (in military designs, I don't know about GenX.); this shortens the engine (less weight) and simplifies the design (fewer parts). But there is a noticible hit in TSFC in reduced power operation (4 to 6%)! In the case of the F-22 this cut the subsonic ferry range too much. Theoretically, you could optimize the airfoils so that no stator is needed, but no one has done it right yet.

Quoting Caboclo (Reply 16):
EMBQA, what's the difference between shafts and spools?

Depends on the engine company. At Pratt, a Spool includes the following parts: Compressor rotor and blades, shaft (tube that bearings ride on and connect compressor rotor to turbine rotor press fitted into rotors), bearings, turbine rotor and blades. However, that's Pratt. I cannot speak for other corporate cultures.

Quoting Finkenwerder (Reply 9):
Rolls Royce did it 30 years ago with the Pegasus ............Counter rotating shafts !!

An amazing design well respected as being ahead of its time by the rest of the industry.

I was turned on to this thread a bit late. Hope the info is useful.

Lightsaber
"They did not know it was impossible, so they did it!" - Mark Twain
 
F14D4ever
Posts: 306
Joined: Sat May 07, 2005 3:20 am

RE: Always Same Rotation On 2-shaft Engines?

Sat Jun 11, 2005 5:26 am

Lightsaber, another great post!

Quoting Lightsaber (Reply 18):
Theoretically, you could optimize the airfoils so that no stator is needed, but no one has done it right yet.

I can't imagine it could be done with airfoil optimization alone. Speed-speed matching is important and could presumably be improved via mods to the vsv schedules.
"He is risen, as He said."
 
efohdee
Posts: 212
Joined: Fri Oct 29, 2004 4:52 am

RE: Always Same Rotation On 2-shaft Engines?

Mon Jun 13, 2005 8:06 am



I answered my own question. Look at the turbine section.
 
efohdee
Posts: 212
Joined: Fri Oct 29, 2004 4:52 am

RE: Always Same Rotation On 2-shaft Engines?

Mon Jun 13, 2005 8:35 am

Who is online

Users browsing this forum: No registered users and 9 guests