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Is The LM 2500 A Turbo Jet Version Of The CF-6?  
User currently offline747400sp From United States of America, joined Aug 2003, 3480 posts, RR: 2
Posted (8 years 1 month 3 weeks 3 days 7 hours ago) and read 17247 times:

Hello

I saw some photos of the LM-2500 Gas Turbine. These gas turbin are on DDG 51, AOE 6, CG-47 and FFG-7 class ship in the USN. They also used on cruise ships, even the giant beauty, the RMS Queen Mary 2. The LM-2500 do not have a fan they look a turbo jet. Even though I know the LM-2500 will never hit, the skies I just wanted to know is the LM-2500 bacisly a turbo jet version of the CF-6?



PS: I have had to help moore up some DDG-51, CG-47 and FFG-7 class ships pier side, and you can hear these LM-2500 though the hull.

32 replies: All unread, showing first 25:
 
User currently offlineAeroWeanie From United States of America, joined Dec 2004, 1607 posts, RR: 52
Reply 1, posted (8 years 1 month 3 weeks 3 days 7 hours ago) and read 17258 times:
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The LM2500 is just like a CF6, except the modified low pressure turbine now drives an output shaft, rather than the fan.


http://emcon-systems.com/images/GE.LM2500.Gas.Turbine.jpg


User currently offlineWoodreau From United States of America, joined Sep 2001, 1017 posts, RR: 6
Reply 2, posted (8 years 1 month 3 weeks 2 days 14 hours ago) and read 17195 times:

The LM 2500 is a single spool turbofan and is a derivative of the TF-39 engine and like Aeroweenie said the LP turbine instead of running through the engine to drive the N1 fan, runs aft and is connected to a reduction gear through a triple-S clutch - 2 LM 2500 engines to one reduction gear and one propeller.

The clutch allows the engines to be shut down while the propeller still turns or allows one LM2500 engine to drive the reduction gear and propeller with the other LM 2500 engine shutdown.

Normal configuration for cruise across the pond is for one engine out of the 4 to be "online" driving one propeller, the other propeller is "trailed" - it just free spins due to the water flowing through it - kind of like running your other engine shutdown but not feathered.



Bonus animus sit, ab experientia. Quod salvatum fuerit de malis usu venit judicium.
User currently offlineIFIXCF6 From United States of America, joined Sep 2004, 108 posts, RR: 0
Reply 3, posted (8 years 1 month 3 weeks 2 days 2 hours ago) and read 17141 times:

The LM2500 is an "aeroderivative" of the CF6-6, the LM5000 of CF6-50, and the LM6000 of the CF6-80.

Mike


User currently offlineFLY2HMO From , joined Dec 1969, posts, RR:
Reply 4, posted (8 years 1 month 3 weeks 1 day 22 hours ago) and read 17120 times:

Quoting Woodreau (Reply 2):
Normal configuration for cruise across the pond is for one engine out of the 4 to be "online" driving one propeller, the other propeller is "trailed" - it just free spins due to the water flowing through it - kind of like running your other engine shutdown but not feathered.

And why would you want to do that?


User currently offlineStealthZ From Australia, joined Feb 2005, 5678 posts, RR: 45
Reply 5, posted (8 years 1 month 3 weeks 1 day 22 hours ago) and read 17117 times:
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Quoting Woodreau (Reply 2):
Normal configuration for cruise across the pond is for one engine out of the 4 to be "online" driving one propeller, the other propeller is "trailed" - it just free spins due to the water flowing through it - kind of like running your other engine shutdown but not feathered.

And what ship is this on??



If your camera sends text messages, that could explain why your photos are rubbish!
User currently offlineWoodreau From United States of America, joined Sep 2001, 1017 posts, RR: 6
Reply 6, posted (8 years 1 month 3 weeks 1 day 5 hours ago) and read 17090 times:

Quoting FLY2HMO (Reply 4):
And why would you want to do that?

Same reason why airplanes single engine taxi when there is a long delay between the gate and takeoff.  Smile

Trail shaft (one engine online) stills allows the ship (CGs/DDs/DDGs) to do about 20kts. Transit speed of advance across the ocean is usually around 14-16 kts. So that is plenty. The extra speed you get from the other engines is actually very minimal, having a second engine online gets you 25-26kts, bringing #3 and 4 online gets you 30kts. Maybe 31-32kts if you flat out redline the engines. If you needed to keep up with the nuclear powered carrier that's doing 30+kts, well the carrier is leaving you behind like it or not, and you just play catch up with the carrier when you arrive 2-3 weeks later.

So primarily it's a fuel conservation measure -having all the other engines up doesn't make sense when you don't need the speed - being able to shut down the LM 2500 engines also allow the engineers to do the required maintenance on the engines, do a fresh water wash of the turbine, etc.

If you do need the extra speed, the other 3 engines can be brought on line and you have all 4 engines ready to answer all bells within 10 minutes. It's literally aligning the fuel, turning the switch to autostart, and pressing the engine start pushbutton to start the engine start sequence - you can do a cross bleed start from the other engine just like a jet airplane or you do a start using HP air. Watch your Ngg indications and don't exceed T5.4. After the engines stabilize, the engines clutch in automatically and you transfer engine control to the bridge.

If you're doing any formation maneuvering, close in maneuvering or in a potentially hostile area, the readiness condition of the ship is increased, you bring the other engines online and you don't cruise around on one engine.

A FFG is a bit different because it only has 2 LM 2500 engines and just 1 shaft, so there's no trail shaft configuration with the FFG. one LM 2500 engine gets you a 25kt FFG - 2 engines gets you a 29kt FFG.

As for the prop itself, it's either 100% forward pitch or 100% reverse pitch or somewhere inbetween, it doesn't feather like a multi-engine prop plane.



Bonus animus sit, ab experientia. Quod salvatum fuerit de malis usu venit judicium.
User currently offlineFLY2HMO From , joined Dec 1969, posts, RR:
Reply 7, posted (8 years 1 month 3 weeks 1 day 5 hours ago) and read 17076 times:

Quoting Woodreau (Reply 6):
Same reason why airplanes single engine taxi when there is a long delay between the gate and takeoff.

Gotcha. Makes sense.  Smile


User currently offlineStealthZ From Australia, joined Feb 2005, 5678 posts, RR: 45
Reply 8, posted (8 years 1 month 3 weeks 1 day 1 hour ago) and read 17069 times:
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Woodreau,
Getting slightly away from the original topic but if the prop is variable pitch it would not seem like a huge additional engineering task to make them feathering as well. Is this not desireable, perhaps having the shafts turn while at sea keeps bearings lubed etc and prevents other .. for want of the technical terms... bad things happening to shafts, bearings etc!
Just curious

Rgds

Chris

PS thanks for you detailed response above, it was most informative



If your camera sends text messages, that could explain why your photos are rubbish!
User currently offlineWoodreau From United States of America, joined Sep 2001, 1017 posts, RR: 6
Reply 9, posted (8 years 1 month 2 weeks 6 days 15 hours ago) and read 17032 times:

I have no idea why they didn't design a feather position for the props or how hard it would be to do this - it probably is possible.

The props on a warship bear no resembalance to a propeller on an airplane. They are designed to minimize cavitation (not eliminate it) to reduce the chance of detection by submarines but we still get detected anyway. They look more like boomerangs than propellers. The propeller shaft itself is a series of concentric hollow pipes - to provide bleed air from the LM 2500 engines to the propeller for Prairie air (to fill in the vacuum caused the rotation of the prop with air bubbles) and provide control oil to and from the prop hub to control the pitch angle of the propeller blade.

But yes you don't want to stop a shaft underway except in extraordinary circumstances. The shaft itself between the reduction gear/thrust bearing and the propeller can vary from several dozens of feet to several hundred feet long (in the case of an aircraft carrier). It is supported by line shaft bearings - in between the line shaft bearings, the shaft if locked and not allowed to spin (over a long period of time) eventually will bow (an extreme analogy is the suspension cables on a suspension bridge you can try to stretch those cables as tight as you can, but the cables will never be perfectly straight) - the same goes for the shaft. Once it bows, when you spin the shaft - well it's not balanced anymore like an unbalanced load in your washing machine.

Once a ship is underway, it's a relatively dangerous procedure to "lock" the shaft in place. It involves engaging something called a jacking gear - the jacking gear is used in port to keep the shaft turning at like 2 rpms every 12 hours and for other uses as well. So you don't lock the shaft except in extraordinary circumstances - like loud metallic noise in the reduction gears or uncontrolled flooding through the stern tube requiring inflation of the shaft seal, etc. It just much easier to keep the prop free spinning underway - it allows the lineshaft bearings to stays lubed like you said and it keeps the shaft turning to prevent bowing.



Bonus animus sit, ab experientia. Quod salvatum fuerit de malis usu venit judicium.
User currently offlineStealthZ From Australia, joined Feb 2005, 5678 posts, RR: 45
Reply 10, posted (8 years 1 month 2 weeks 6 days 6 hours ago) and read 17007 times:
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Thanks Woodreau,

Figured it would have been something like that, All makes sense to me.

Regards

Chris



If your camera sends text messages, that could explain why your photos are rubbish!
User currently offlineOryx From Germany, joined Nov 2005, 126 posts, RR: 0
Reply 11, posted (8 years 1 month 2 weeks 5 days 17 hours ago) and read 16981 times:

Some applications of "aero derivatives" I remember are power generation in small plants, propulsion of trains and ships or driving compressors for gas pipelines. I once spoke to en engineer who designs gas turbines for larger power plants. He said that there is nearly no chance to compete with the engine makers in the market for smaller turbines (i.e. less than let's say 50 MW) due to the greater production numbers of jet engines.

Only to nitpick: these engines are not turbo-jet but turbo-shaft.


User currently offlineSprout5199 From United States of America, joined Feb 2005, 1851 posts, RR: 2
Reply 12, posted (8 years 1 month 2 weeks 5 days 15 hours ago) and read 16973 times:

Quoting Woodreau (Reply 9):
I have no idea why they didn't design a feather position for the props or how hard it would be to do this - it probably is possible.

I was on the USS Flatley(FFG-21), and we could "feather" the screw. And IIRC we could do about 18 knots on 1 engine, and 30+ on two(seen much higher actually, just not for long).

Quoting Woodreau (Reply 6):
As for the prop itself, it's either 100% forward pitch or 100% reverse pitch or somewhere inbetween

And when when we did a crash back(100% foward to 100% back) the stern would jump up about 10 feet and crash back down, broke a lot of stuff but would stop the ship from full ahead in about one and a half lengths of the ship(nice to have if your gonna run into a bigger ship)

Dan in Jupiter


User currently offlineEssentialpowr From United States of America, joined Sep 2000, 1820 posts, RR: 2
Reply 13, posted (8 years 1 month 2 weeks 5 days 9 hours ago) and read 16957 times:

Woodreau knows his stuff; we share a similar background as I was EOOW qual'd on an FFG7.

Quoting Sprout5199 (Reply 12):
I was on the USS Flatley(FFG-21), and we could "feather" the screw.

Nope, the first 3-5 kts of forward TLA changed pitch only on the blades, but none of the LM-2500 powered ships can feather a screw, probably b/c of the massive forces required to unfeather it when a 4000 - 9000 ton ship is traveling at 15 kts or greater.


User currently offlineSprout5199 From United States of America, joined Feb 2005, 1851 posts, RR: 2
Reply 14, posted (8 years 1 month 2 weeks 5 days 5 hours ago) and read 16948 times:

Quoting Essentialpowr (Reply 13):
Nope, the first 3-5 kts of forward TLA changed pitch only on the blades, but none of the LM-2500 powered ships can feather a screw, probably b/c of the massive forces required to unfeather it when a 4000 - 9000 ton ship is traveling at 15 kts or greater.

I was thinking more of when we were along side the pier, at sea and anchor the screw would turn but no fwd or aft motion. (line 4 line handler, line capt, then fight deck phone talker).

What ship were u on and when? I was on the Flatdog from 1987 to 1991. Was an ET2 (I know a Twigit, Damn Snipes)

Also loved when we were all ahead how the torque would give us a 5-10 degree list to starboard(or was it port, been a few years)

Dan in Jupiter


User currently offlineLitz From United States of America, joined Dec 2003, 1754 posts, RR: 0
Reply 15, posted (8 years 1 month 2 weeks 4 days 10 hours ago) and read 16905 times:
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Quoting Oryx (Reply 11):
Some applications of "aero derivatives" I remember are power generation in small plants, propulsion of trains and ships or driving compressors for gas pipelines.

Turbine powered trains haven't quite made primetime yet ... it's not that they don't have enough power (trains use electrically powered traction motors; doesn't really matter if the electricity comes from a turbine or diesel powered generator) ... it's it's just not yet economical to haul around the fuel required for the turbine. The other problem is, they're not exactly very quiet.

Diesels are still, at this point, more fuel-effecient. And much, much quieter.

More info at : http://en.wikipedia.org/wiki/Gas_turbine-electric_locomotive

- litz


User currently offlineEssentialPowr From United States of America, joined Sep 2000, 1820 posts, RR: 2
Reply 16, posted (8 years 1 month 2 weeks 4 days 5 hours ago) and read 16893 times:

Quoting Litz (Reply 15):
Turbine powered trains haven't quite made primetime yet ... it's not that they don't have enough power (trains use electrically powered traction motors; doesn't really matter if the electricity comes from a turbine or diesel powered generator) ... it's it's just not yet economical to haul around the fuel required for the turbine. The other problem is, they're not exactly very quiet.

What a full service site!! Airliners, ships, and trains!

Check out Union Pacific's site...they had gas turbine locomotives for a while in the 70s. In addition to an absolute requirement for "clean" air, (sometimes hard to botain in dusty yards and low speed conditions) they found that the heat of the exhaust melted asphalt overlays when the locomotives were parked under overpasses...so they went away for a lot of reasons.


User currently offlineOryx From Germany, joined Nov 2005, 126 posts, RR: 0
Reply 17, posted (8 years 1 month 2 weeks 3 days 20 hours ago) and read 16865 times:

Quoting EssentialPowr (Reply 16):
Check out Union Pacific's site...they had gas turbine locomotives for a while in the 70s

The French and the British experimented also with turbine power for trains.

There is realy a lot of exotic applications for jet engines. The burn a lot of different fuels i.e. gas from coal mines or chemical production plants.

I think the most spectacular is to blow out oil-well fires.

Another funny idea is to compress air at times of low electricity demand and store it in underground cavities. When demand rises a gas turbine is driven with the already compressed air.


User currently offline747400sp From United States of America, joined Aug 2003, 3480 posts, RR: 2
Reply 18, posted (8 years 1 month 2 weeks 3 days 8 hours ago) and read 16837 times:

By the way do Supply class AOE or (AOE-6) use there LM-2500 gas turbine all the time, or are part diesel and they use there diesel at slow speeds?

User currently offlineSprout5199 From United States of America, joined Feb 2005, 1851 posts, RR: 2
Reply 19, posted (8 years 1 month 2 weeks 3 days 3 hours ago) and read 16816 times:

Looking it up the AOEs have 4 LM-2500s to power 2 shafts. the five SSDGs are for electric power.

We had 4 SSDGs on the USS Flatley(FFG-21).

IIRC the new DDGs, and CGs have SSTGs(Ship Service Turbine Generators)

Just a little story, we had a helo det onboard once and they had a problem with a turbine, a GSE1 was in the hanger and offered his help, the airdales blew him off in a not so polite way saying "what the hell do you know about turbines?", His reply was " Follow me and I will show you what your turbine will look like when it grows up" Was very funny.

Dan in Jupiter


User currently offlineEssentialPowr From United States of America, joined Sep 2000, 1820 posts, RR: 2
Reply 20, posted (8 years 1 month 2 weeks 2 days 23 hours ago) and read 16805 times:

Quoting 747400sp (Reply 18):
By the way do Supply class AOE or (AOE-6) use there LM-2500 gas turbine all the time, or are part diesel and they use there diesel at slow speeds?

From the Navy web site:


General Characteristics, Supply Class

Builder: National Steel and Shipbuilding Co., San Diego, CA.
Propulsion: Four GE LM2500 gas-turbines; 2 shafts; 105,000 hp.
Length: 754 feet (229.9 meters).
Beam: 107 feet (32.6 meters).
Displacement: 48,800 tons (49,583.15 metric tons) full load.
Speed: 25 knots.
Crew: 160 civilians, 29 military.

CODOG is an acroynm for Combination Diesel or Gas turbine...several foreign navy frigates, as well as a US Coast Guard class, utilize this arrangement for main propulsion. Not so for the AOE 6 class, they are exclusivly gas turbine for main propulsion.


User currently offlineWoodreau From United States of America, joined Sep 2001, 1017 posts, RR: 6
Reply 21, posted (8 years 1 month 2 weeks 2 days 14 hours ago) and read 16787 times:

The difference between an AOE-6 and the CG/DD/DDG/FFGs is that AOE-6 doesn't have reverse pitch. They have a different mechanism to make the shaft turn the opposite direction. I never really understood the concept and I never had the chance to talk to an engineer on one of those ships to understand the actual mechanics of how they get the shaft to go backwards.

The CGs/DDGs actually have GTG's for electrical power - Gas Turbine Generators, not SSTGs. It's an Allison centrifugal flow gas turbine (more like an APU on an aircraft) as the prime mover for the generator. A SSTG is a steam turbine - 1950's-60's technology - found the older steam and nuclear powered Belknap/Leahy class CGs/Virginia class CGNs/Adams class DDGs and on current day CVNs/LHAs/LHDs - the abbreviation is right though  

The CGs/DDs have waste heat boilers on the exhaust side of the GTG, so they still have steam powered components for utilities and water purification. The FFGs and DDGs don't have boilers so their utilities are all electric and reverse osmosis is used for water purification. (Well I might be fuzzy on the FFG)

[Edited 2006-06-08 16:33:07]


Bonus animus sit, ab experientia. Quod salvatum fuerit de malis usu venit judicium.
User currently offline747400sp From United States of America, joined Aug 2003, 3480 posts, RR: 2
Reply 22, posted (8 years 1 month 2 weeks 2 days 12 hours ago) and read 16775 times:

On AOE-6 class ships the shaft do turn inside a shaft. From what I been told an AOE-6 ship has two prop on each shaft that trun in different direction.

User currently offlineSprout5199 From United States of America, joined Feb 2005, 1851 posts, RR: 2
Reply 23, posted (8 years 1 month 2 weeks 2 days 11 hours ago) and read 16770 times:

Quoting Woodreau (Reply 21):
The FFGs and DDGs don't have boilers so their utilities are all electric and reverse osmosis is used for water purification. (Well I might be fuzzy on the FFG)

IIRC FFGs have electric evaps(been 15 years). I learned to clean the salinity sensors to help the IC's in our shop. FFG's had weird crews, IC men were part of the Electronics shop, so I learned a lot about snipe land. Plus we were minium manned so I even stood engineer watches inport(an ET taking soundings and pumping cht, what fun)

Quoting Woodreau (Reply 21):
The CGs/DDGs actually have GTG's for electrical power

I was close, knew they were gas turbines.  Smile

Dan in Jupiter


User currently offlineFLY2HMO From , joined Dec 1969, posts, RR:
Reply 24, posted (8 years 1 month 2 weeks 1 day ago) and read 16725 times:

Quoting Oryx (Reply 17):
There is realy a lot of exotic applications for jet engines.

No kidding, this one guy made one of those home-made jet engines out of a automotive turbocharger, but he fuels it with wood  eyepopping 

http://www.nyethermodynamics.com/nt6/index.html

Here's a direct link to some videos of it:

http://www.nyethermodynamics.com/nt6/videos/NT6%20Tour%20(Med-Res).wmv

http://www.nyethermodynamics.com/nt6...ideos/NT6%20Run-UP%20(Med-Res).wmv

I've started a project for making a homebuilt jet engine, but with college and all that stuff I just dont have the time to complete it.  Sad


25 EssentialPowr : Woodreau, your work on this thread has been flawless, up till now. An SSTG is a Ship's Service Turbine Generator, with the acronym used on the Spruca
26 Post contains images Litz : One of the episodes of Junkyard Wars they made Junkyard Dragsters. Yep, full-scale top-fuel equivelant dragsters made from junk. One unit was traditi
27 Oryx : At an enterprise making large-scale turbochargers for ship diesels they are doing something along that line in order to test the turbocharger. They s
28 Dougloid : As part of my job at Delavan I did some market research on the subject of aero derivative turbine powerplants and their locations. Many of them are u
29 EssentialPowr : As stated, the GE LM 2500 is marketed as a prime mover for electrical power generation...that was an original application for it; unit costs are large
30 747400sp : It just hit me, the LM 2500 is an Aft fan version of the TF-39.
31 L-188 : The gas crisis is what really did them in, the generators and traction motors ended up in U50 locomotives, which had fairly short lives due to crappy
32 Post contains images JetMech : Thanks for the very interesting thread techies, more please ! . Regards, JetMech
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