CF188A
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Most Powerful Aircraft Powerplant Ever Designed?

Mon Dec 04, 2006 11:22 am

Simple question... i apologize if it has been discussed before. I could not find anything in the search function so here is the simple question.

What is the most powerful jet engine/ turbofan every manufactured in aviation? I understand that the B1B , F-22. and 777/380 are way up there in rank, however lets throw come fascinating ones out here Smile

Thanks
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jetmech
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Mon Dec 04, 2006 11:27 am

The mighty GE90-115B? Definitely the most powerful turbofan in production and commercial use.
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N231YE
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Mon Dec 04, 2006 11:49 am

Quoting CF188A (Thread starter):
jet engine

I might be stretching it a bit, but if you consider a jet engine as a gas turbine, than that would include turboprops

I believe the most powerful turboprop is either the Kuznetsov NK-12 that powered the Tupolev Tu-95 Bear, or the Pratt & Whitney XC-15(?) [I can't think of the actual model designation], which the JT3 was based off of.

As for a turbofan, the GE90-115 would be my best guess
 
CF188A
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Mon Dec 04, 2006 12:02 pm

IF THIS THREAD CONTINUES.... if possible post thrust specifications and the whole works  Smile . Also lets narrow it down to turbofans and jets  Smile What comes fairly close to the GE90-115 ?
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Molykote
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RE: Most Powerful Aircraft Powerplant Ever Designe

Mon Dec 04, 2006 12:23 pm

Power = Force (Basically Thrust) X Velocity

GE90-115B, Boeing 777
115 klbs each engine @ 0.8M
(M = 295 m/s @ 40,000 ft)

Pratt and Whitney J58, Lockheed SR-71
32 klbs each engine @ 3.2M
(M = 298 m/s @ 80,000 ft)

I haven't touched these kind of calculations in about 4 years but knock yourselves out people......

PS - I wouldn't disagree with anyone who called the GE90-115B the most powerful engine in the world.
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HaveBlue
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Mon Dec 04, 2006 12:33 pm

Quoting Molykote (Reply 4):
Pratt and Whitney J58, Lockheed SR-71
32 klbs each engine @ 3.2M
(M = 298 m/s @ 80,000 ft)

Gotta love that a 47 year old design is still in contention for most powerful engine ever on an airplane. Kelly and the Skunk Works, unbelievable.
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N231YE
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Mon Dec 04, 2006 12:48 pm

Quoting Molykote (Reply 4):
PS - I wouldn't disagree with anyone who called the GE90-115B the most powerful engine in the world.

No fair, the P&W J58 on the SR-71 operates as a ramjet at high speeds/altitudes, so its not a true jet engine  smile 
 
sprout5199
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Mon Dec 04, 2006 1:14 pm

Quoting CF188A (Thread starter):
Most Powerful Aircraft Powerplant Ever Designed?

I would have to say Project Pluto
http://en.wikipedia.org/wiki/Project_Pluto

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Molykote
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Mon Dec 04, 2006 1:37 pm

Quoting N231YE (Reply 6):
No fair, the P&W J58 on the SR-71 operates as a ramjet at high speeds/altitudes, so its not a true jet engine

It's a true jet engine (as are all ramjets).

It may not function as a typical turbine engine at higher speeds but the J58 is (without a doubt) a jet engine.


Main Entry: jet engine
Function: noun
: an engine that produces motion as a result of the rearward discharge of a jet of fluid; specifically : an airplane engine that uses atmospheric oxygen to burn fuel and produces a rearward discharge of heated air and exhaust gases -- see AIRPLANE illustration

(www.m-w.com)
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3DPlanes
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Mon Dec 04, 2006 11:22 pm

Quoting Molykote (Reply 4):
Pratt and Whitney J58, Lockheed SR-71
32 klbs each engine @ 3.2M
(M = 298 m/s @ 80,000 ft)

The new PW F135 engine for the F-35 series has made 40,000 lbs in full burner...

Took 'em long enough to make a better mouse trap, eh?
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N231YE
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Mon Dec 04, 2006 11:49 pm

Quoting Molykote (Reply 8):

You are correct, but I was thinking of the engines that has moving mechanical parts (turbojet, turboprop, turbofan)

Has anyone mentioned that the most powerful turbojets were the GE (not sure of the model/numbers) that were to power the Boeing SST.
 
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jetmech
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Mon Dec 04, 2006 11:50 pm

Quoting Molykote (Reply 4):
Power = Force (Basically Thrust) X Velocity

I'm not too sure if power calculations based on the maximum velocity of the aircraft and the nominal maximum thrust of the engine are valid. At cruise speeds and altitude, the thrust of the GE90-115B is much less than 115K; with GE quoting 11,000lbs of thrust.

http://www.geae.com/education/engines101/

I would presume that a similar phenomenon may exist for the SR-71  Confused .

Regards, JetMech
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BoeingOnFinal
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Tue Dec 05, 2006 12:23 am

Which commercial aircraft has the best power-to-weight ratio at empty weight?
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Starlionblue
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Tue Dec 05, 2006 12:31 am

Quoting BoeingOnFinal (Reply 12):
Which commercial aircraft has the best power-to-weight ratio at empty weight?

Concorde?
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BoeingOnFinal
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Tue Dec 05, 2006 1:11 am

I would assume that an aircraft that could hold alot of cargo and passengers, would have much more power to spare when Empty. And the Concorde doesn't have either of those qualities. Unless it has alot of power to spare when at MTOW.
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Molykote
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Tue Dec 05, 2006 1:27 am

Quoting JetMech (Reply 11):
I'm not too sure if power calculations based on the maximum velocity of the aircraft and the nominal maximum thrust of the engine are valid. At cruise speeds and altitude, the thrust of the GE90-115B is much less than 115K; with GE quoting 11,000lbs of thrust.

http://www.geae.com/education/engines101/

I would presume that a similar phenomenon may exist for the SR-71 .

Regards, JetMech

JetMech:

I've seen some of your other posts and it appears you are quite knowledgeable so I'm sure you're aware of the factors affecting thrust and engine performance. You certainly do point out a deficiency in my earlier post. I apologize if my post appeared to suggest that striaght multiplication of the numbers I listed (without altitude/airspeed/etc correction factors) would yield the effective power output of the engine/application pairings. This was not my intent but I can see how my post may have been misleading.

The effects you cite are why I didn't implement my example numbers in the basic equation that I cited (but provided them as parameters). It's also why I noted that I hadn't crunched the numbers since college and didn't feel like pulling out the old formulas  

The larger intent of my post was to make the FORCE vs POWER distinction and to note that the F x V formula will provide the amount of power being output by an engine(s)/application. Anyone interested can Google for "thrust vs altitude" or similar verbiage and probably find some nice explanations and/or graphs.

JetMech's observations are spot on.

Edit: Noted respect for JetMech for calling attention to my misleading post  whistleblower 

[Edited 2006-12-04 17:34:35]
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timz
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RE: Most Powerful Jet

Tue Dec 05, 2006 2:08 am

I'm guessing today's big turbofans can't compare with B-70/SST engines for actual power, tho they of course exceed their static thrust. But power is force times speed-- "static thrust" implies zero useful power.

This isn't conclusive, but: consider a 767 loaded to 150,000 kg take-off weight, with two 60000-lb engines. How long will it take to get to 9000 meters altitude, from a standing start on the runway? At least ten minutes, right?

But a B-1B set a time-to-climb record in the 150-tonne class: 9000 meters in less than four minutes. Yet its static thrust in afterburn is no greater than the 767's.

[Edited 2006-12-04 18:13:40]
 
Fly2HMO
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Tue Dec 05, 2006 2:37 am

Quoting Molykote (Reply 4):
I wouldn't disagree with anyone who called the GE90-115B the most powerful engine in the world.

Maybe thats because it is... 

IIRC back when they were testing the -115B they took it up momentarily to 127K pounds of thrust.

We're talking about which engine makes the most thrust, right? Then it would have to be the GE-90 AFAIK

I wonder if GE is considering an afterburning GE-90 for the military... Now that would be raw power   

[Edited 2006-12-04 18:54:41]
 
3DPlanes
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Tue Dec 05, 2006 7:19 am

Quoting Timz (Reply 16):
But a B-1B set a time-to-climb record in the 150-tonne class: 9000 meters in less than four minutes. Yet its static thrust in afterburn is no greater than the 767's.

While the weights and thrust may be equal, and it makes an interesting comparison, I'd wager the shape of the airframes had more influence. When they do those time-to-climb record flights, the actual climb is usually the very last thing they do. The first part of that B-1 climb would be a low-level acceleration to some speed waaaaay past the 767s Vne, followed by a near-vertical climb to altitude.

And, to counter the old "no work is done" argument - remember that a LOT of air is being sucked in and accelerated backwards to a high velocity.

And maybe one of the aero folks here can correct me, but I've always assumed that static thrust is NOT the best these engines can do. They're spending an awful lot of energy just trying to breathe. There's got to be an optimum speed where ram effect makes the engine more efficient (and powerful?) than at static.
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Starlionblue
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Tue Dec 05, 2006 7:27 am

Quoting FLY2HMO (Reply 17):
We're talking about which engine makes the most thrust, right? Then it would have to be the GE-90 AFAIK

Well, the topic says "powerful aircraft powerplant", not "most thrust".  Wink

Quoting FLY2HMO (Reply 17):
I wonder if GE is considering an afterburning GE-90 for the military... Now that would be raw power

Indeed, but if you want to use it for supersonic flight (why else would you need the burner) that fan would be sooo in the way.
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speedracer1407
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Tue Dec 05, 2006 10:43 am

Quoting Molykote (Reply 15):
The larger intent of my post was to make the FORCE vs POWER distinction and to note that the F x V formula will provide the amount of power being output by an engine(s)/application.

For reciprocating engines, power (Horsepower, specifically) is calculated by the following: Torque x RPM/5252 --
Thus, power is a calculation of both force and time: hence why a small, low-torque, high-revving engine can produce high horsepower without high force.

Is there a direct relationship between this (hopefully correct) understanding of recip force and power and the relationship between jet thrust and power? Why is velocity an element of power calculations of jet engines?

O
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T prop
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Tue Dec 05, 2006 10:51 am

This one.


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Molykote
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Tue Dec 05, 2006 12:29 pm

Quoting 3DPlanes (Reply 18):
And, to counter the old "no work is done" argument - remember that a LOT of air is being sucked in and accelerated backwards to a high velocity.

I understand your point and certainly agree that air is being (heavily worked) through the flowpath. However, under static conditions this does not represent useful power for an aircraft.

If my car engine block reaches a temperature of 200 degrees under operation, this represents a large amount of energy that is doing nothing to help propel my car down the road.

Regardless,
It is evident that you, I, and others in this thread are capable of making the distinctions required by physical definitions of work, energy, force, etc. This is all I wished to point out in my first post. I also did acknowledge that I have no problem associating thrust capability with "power".
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flametech21
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Tue Dec 05, 2006 1:27 pm

If I remember correctly, there is a Trent variant that goes over 100,000lbs of thrust. Still doesn't even come close to the 115,000 of the GE90-115B, though.
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HAWK21M
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Tue Dec 05, 2006 5:59 pm

GE90-115 with 115lbs of thrust.
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HAWK21M
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Tue Dec 05, 2006 6:00 pm

GE90-115 with 115lbs of thrust.
regds
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F14D4ever
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RE: Most Powerful Aircraft Powerplant Ever Designe

Tue Dec 05, 2006 9:53 pm

Quoting Speedracer1407 (Reply 20):
Why is velocity an element of power calculations of jet engines?

Because power is an instantaneous rate of energy transfer; its units are [energy/unit time]. In a jet engine, energy conversion and transfer rates are products of gas velocity.

Quoting 3DPlanes (Reply 18):
And maybe one of the aero folks here can correct me, but I've always assumed that static thrust is NOT the best these engines can do. They're spending an awful lot of energy just trying to breathe. There's got to be an optimum speed where ram effect makes the engine more efficient (and powerful?) than at static.

I encourage everyone in the Tech/Ops arena to at least try to understand the distinction between 'force' and 'power' because they each denote different, specific, and meaningful quantities. You'll enjoy the experience more with a better grasp of the terminology.

3D, your intuition is essentially correct, but incomplete. Ram effect makes a jet engine more 'forceful', in that the gross thrust (force) out the back increases with flight velocity, but that's only part of the story. Ultimately we're more interested in net thrust, which is gross thrust minus ram drag. Ram drag is the force on the front of the engine due to intake of air. You'll never see higher net thrust than at ground level static conditions. The moment the engine starts moving through the air is the moment net thrust starts decreasing, because ram drag increases faster than gross thrust.
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darkblue
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Tue Dec 05, 2006 11:11 pm

Quoting Molykote (Reply 4):
Power = Force (Basically Thrust) X Velocity

GE90-115B, Boeing 777
115 klbs each engine @ 0.8M
(M = 295 m/s @ 40,000 ft)

Pratt and Whitney J58, Lockheed SR-71
32 klbs each engine @ 3.2M
(M = 298 m/s @ 80,000 ft)



Quoting JetMech (Reply 11):
At cruise speeds and altitude, the thrust of the GE90-115B is much less than 115K; with GE quoting 11,000lbs of thrust.

Thrust is nearly inversely proportional to altitude (or proportional to ambient pressure). This makes it quite easy to estimate top of climb thrust (the maximum thrust at cruise altitude). JetMech, please note that the numbers you've quoted from GE are for an average cruise thrust, not maximum thrust. An estimate for max thrust at 40,000ft would be:

2.72psia / 14.696 psia * 115,000 lbf = ~21300lbf

I suppose you could something similar for the J58 thrust, but I honestly don't know if this same rule of thumb holds true for supersonic / ram jet engines. Anybody else have any idea what the max thrust is for the SR-71 at 80,000ft? Or what the drag is on the aircraft at supersonic speeds?
 
Areopagus
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Wed Dec 06, 2006 2:47 am

Quoting Speedracer1407 (Reply 20):
Is there a direct relationship between this (hopefully correct) understanding of recip force and power and the relationship between jet thrust and power? Why is velocity an element of power calculations of jet engines?

You can apply lifting force to a car with a jack. The energy put into it (work)is force (= the car's weight) times the distance lifted. The power is the rate work is being done, which is force times the rate of displacement (force * speed). If you stop pumping the jack, it is still applying force equal to the car's weight to the bottom of the car, but no work is being done.

If a jet engine is run at full power on an aircraft that is not moving (yet), a lot of power is being applied to blow air backwards, but that power is lost to the aircraft, as no useful work is being done on it -- as others have noted. This is also true of a piston engined aircraft, but in that case, the engine's power is cited as the amount of power turning the propeller. I have seen the 787's GEnx engine cited as producing 25,000 shaft horsepower. That is the power turning the fan, just as a recip applies power to the prop. I'll bet 25,000 shaft horsepower considerably exceeds the Tu-95's engine's output.
 
CF188A
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Wed Dec 06, 2006 6:11 am

Quoting Areopagus (Reply 28):
You can apply lifting force to a car with a jack. The energy put into it (work)is force (= the car's weight) times the distance lifted.

work = F DELTA D .. . force x displacement. work done and the force applied should not be mixed up... the proof of this is one is in Joules and one is in Newtons. Work (J) and FOrce(N) .

Quoting Areopagus (Reply 28):
The power is the rate work is being done, which is force times the rate of displacement (force * speed). If you stop pumping the jack, it is still applying force equal to the car's weight to the bottom of the car, but no work is being done.

No the physics term for this would be impulse IN N.s The amount of time it takes for a specific force to act/transfer it's energy on another object in an enclosed system. You could view the aircraft itself as one enormous enclosed system. Don't forget that If you have an old Cadillac going 60 MPH into a brick wall the people will be killed instantly. If you have a new BMW / Volvo however, their crumple zones increase the amount of time energy is transferred and therefore the chances of survival increase.

Quoting Areopagus (Reply 28):
If a jet engine is run at full power on an aircraft that is not moving (yet), a lot of power is being applied to blow air backwards, but that power is lost to the aircraft,

best to use to the term "energy transformation" as it is lost to friction seeing as how the plane has not yet begun its take off roll and the brakes / hydraulics/neumatics keeping the aircraft in a balanced hold position.

For those of you who cannot get the terms right.... Momentum is the product of an objects mass times it's velocity. in kg.m/s .
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Areopagus
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Wed Dec 06, 2006 7:09 am

CF188A, it sounds like you say I'm wrong, but then restate what I said.  Confused Just for the record, I will state that work is the integral of F dot dS, where F is the force vector and dS is the infinitesimal displacement vector. Power is the time derivative of work.
 
CF188A
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Wed Dec 06, 2006 9:30 am

It sounded like you made the work and the resultant force the same thing which is incorrect. You also did not state the term impulse which is the correct terminology. However other than that your 100% correct
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Areopagus
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Wed Dec 06, 2006 9:49 am

Quoting CF188A (Reply 31):
It sounded like you made the work and the resultant force the same thing which is incorrect.

Now I see that you were misled as to my meaning by a lack of parenthesization. Let me rewrite that sentence as:
The energy put into it, or work, is { force times the distance lifted} (that force being the car's weight).
I hope that is more clear.
 
jetlife2
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Wed Dec 06, 2006 11:31 am

You two are "in violent agreement" as we say.

Not to get dragged into power vs force definition discussions, which should now be clear, I will answer the original thread starter as follows, choosing to believe that this answer meets the intent of the original question:

For the record, the GE90-115B has been recorded at 127,900lbf of static thrust and therefore holds the world record for thrust, according to the Guinness Book.

This is somewhat above its rated thrust  Wink

[Some people have the best toys]

Interesting that this very same engine type, rated slightly lower to 110B, powered the -200LR Record Flight a year ago a distance of 11,664nm. Thus earning itself a second entry in the Guinness book. Quite an achievement in a different dimension - efficiency - vs. raw thrust - and a testament in both cases to what can be done with a high bypass cycle.
My views are not necessarily the views of the GE Company
 
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jetmech
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Wed Dec 06, 2006 12:16 pm

G'day Techies  Smile,

I've been having a think about this one, and I believe that there are currently three main schools of thought as to the interpretation of this topic.

Quoting Molykote (Reply 4):
Power = Force (Basically Thrust) X Velocity



Quoting Molykote (Reply 22):
However, under static conditions this does not represent useful power for an aircraft.

I believe that this definition of power is dealing with engine / airframe combinations. I am not too sure if it is the intended definition of power for this topic, as this represents the power required for the airframe / engine combination to maintain a given velocity. Imagine an ultralight with a single cylinder Rotax engine, and a B773ER with a pair of GE90-115B's.

Under this definition, an ultralight rolling down the runway will be more "powerful" than a pair of GE90-115B's at full song being held stationary against the brakes of the B773ER! This is certainly true under this definition, which quantifies the effective power being delivered to produce forward motion of an airframe, but I think it may be beyond the intrinsic "theme" of this topic.

Quoting Speedracer1407 (Reply 20):
Torque x RPM/5252 --
Thus, power is a calculation of both force and time.
Is there a direct relationship between this (hopefully correct) understanding of recip force and power and the relationship between jet thrust and power? Why is velocity an element of power calculations of jet engines?

I believe that this definition is dealing with shaft-power before it gets converted to thrust. In the case of a general aviation type aircraft, it is the shaft power of a reciprocating engine before it is converted to thrust by a propeller. In the case of a commercial airliner, it is the shaft power of a number of turbine stages before it is converted to thrust by the fan. The metric version of the formula relating power, torque and RPM is; Power (watts) = Torque (Nm) * RPM (radians / sec).

Thrust Horsepower (THP) can be used to determine the amount of horsepower required to propel an aircraft at a given velocity instead of using thrust. In US units,

THP = [F * Aircraft speed (MPH)] / [375 (mile*lb / hr)]
THP = [F * Aircraft speed (ft / sec)] / 550

where F = engine thrust at engine mounts in lbs

THP in metric units would probably be called Thrust Kilo Watts (TKW),

TKW = [F (N) * Aircraft speed (m / s)] / 1000

This school of thought as to quantifying power again relies upon the velocity of an airframe / engine combination when converting to THP or TKW, and a measure of the effective (useful) power being delivered to the airframe.

Quoting FLY2HMO (Reply 17):
We're talking about which engine makes the most thrust, right?



Quoting Molykote (Reply 22):
It is evident that you, I, and others in this thread are capable of making the distinctions required by physical definitions of work, energy, force, etc.



Quoting F14D4ever (Reply 26):
You'll never see higher net thrust than at ground level static conditions.



Quoting Areopagus (Reply 28):
If a jet engine is run at full power on an aircraft that is not moving (yet), a lot of power is being applied to blow air backwards, but that power is lost to the aircraft, as no useful work is being done on it -- as others have noted.

I am leaning mostly towards this third school of thought as to the definition of a powerful aero-engine. I agree that no useful power is being delivered for the purposes of propelling an airframe / engine combination, but the amount of work being done on the air going through the engine is immense. The rate at which this work is being delivered is also fantastic, which corresponding means that much power is being delivered by the engine. I am leaning towards maximum static thrust as the definition of powerful for two reason. Firstly, my interpretation of the topic is powerful engine, not airframe / engine combination, secondly, thrust is the useful quantity we want from an aero engine.

Quoting DarkBlue (Reply 27):
JetMech, please note that the numbers you've quoted from GE are for an average cruise thrust, not maximum thrust. An estimate for max thrust at 40,000ft would be:
2.72psia / 14.696 psia * 115,000 lbf = ~21300lbf

Point taken DarkBlue, I did quote that figure from GE without question, but I also have a query with the approximate figure of 21,300lbf.

One of the formulas I am most familiar with with respect to thrust calculations is Thrust = [mdot * (Vin - Vex)]. In metric units, thrust is in Newtons, mdot is the mass flow rate of air through the engine in kg/sec and Vin and Vex are the air velocities at engine inlet and exhaust in metres / sec respectively. I am a bit rusty with US units in this situation, but I assume that thrust would be in lbf, mdot would be in lb / sec and Vin and Vex would be in ft/sec  Confused.

Quoting F14D4ever (Reply 26):
The moment the engine starts moving through the air is the moment net thrust starts decreasing, because ram drag increases faster than gross thrust.

With respect to the information quoted by F14D4ever, the maximum thrust of the GE90-115B is being delivered under static conditions presumably at standard sea level conditions. Thus, I would assume that Vin in the thrust formula is zero Confused.

The figure of 21,300lbs thus seems to be calculated based upon the same static conditions. The cruise altitude of 40,000ft has been adjusted for by the 2.72psia / 14.696psia correction factor, but what about the inlet and exhaust velocities due to cruise speed?

I don't know if I can assume that the maximum exhaust velocity remains constant with increasing aircraft velocity and ram effects, but if it does, the cruise thrust figure will also be reduced due to the fact that the inlet velocity is no longer zero, but perhaps at a figure of 300m / s (984 ft / sec).

I thus seem to think that the maximum cruise thrust figure may be somewhere in the range of 21,300 - 11,000 lbf. Perhaps it may be something like 17,000 - 18,000 lbf  Confused.

Anyway Techies, the above ramblings are just my thoughts on this fascinating topic, with all errors and mis-interpretations being solely on my own shoulders  Smile. As always, I post in the spirit of informed debate and all my comments are delivered with best intentions. For the above reasons, I am leaning mostly towards a static thrust figure as the definition of a powerful aero-engine, and thus, my vote still goes to the GE90-115B!


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Areopagus
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Wed Dec 06, 2006 2:09 pm

Quoting JetMech (Reply 34):
I am a bit rusty with US units in this situation, but I assume that thrust would be in lbf, mdot would be in lb / sec and Vin and Vex would be in ft/sec .

You've got the right idea, except that the English unit of mass is the slug; so mdot is in slugs/sec
 
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Wed Dec 06, 2006 3:16 pm

Let's look at it this way. Suppose a 350,000 kg aircraft accelerates on its takeoff run to 150kt = 77m/s in 35 seconds. (I imagine these numbers are roughly representative of a 773er.) Its kinetic energy gained is 0.5 * 350000 kg * (77m/s)^2 = 1037 megaJoules. Divide that by 35 seconds and you get the average power applied over the takeoff run = 29645000 watts = 29645 kilowatts = 39755 horsepower. So each of two engines delivers to the airplane just under 20000 horsepower averaged over the takeoff run. There will of course be losses, so the engine horsepower (mostly shaft horsepower driving the fan) is greater than that.
 
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jetmech
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Wed Dec 06, 2006 3:57 pm

Quoting Areopagus (Reply 36):
Let's look at it this way.

G'day Areopagus  Smile,

I get the feeling that the engines would be delivering more than 20,000 horsepower each to the airframe, as there would also be considerable drag in the later stages of the take off run. I remember reading somewhere on www.geae.com, that the 115K lb thrust of the GE90-115B was equivalent to around 145,000hp  Confused. I am not too sure exactly what this figure was referring to.

Regards, JetMech
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Areopagus
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Wed Dec 06, 2006 4:25 pm

Quoting JetMech (Reply 37):
I get the feeling that the engines would be delivering more than 20,000 horsepower each to the airframe, as there would also be considerable drag in the later stages of the take off run.

True enough.

Quoting JetMech (Reply 37):
I remember reading somewhere on www.geae.com, that the 115K lb thrust of the GE90-115B was equivalent to around 145,000hp

One pound of thrust equals one horsepower when flying at 375mph. Scaling proportionally, 115klb thrust equals 145khp at 472 mph. But that is under the assumption that the engine can actually produce that much thrust at cruise, which is not so.

You can get some pretty big power ratings by evaluating a rocket engine at orbital speed.
 
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Wed Dec 06, 2006 5:52 pm

Quoting F14D4ever (Reply 26):
In a jet engine, energy conversion and transfer rates are products of gas velocity.



Quoting Areopagus (Reply 28):
If a jet engine is run at full power on an aircraft that is not moving (yet), a lot of power is being applied to blow air backwards, but that power is lost to the aircraft, as no useful work is being done on it -- as others have noted.



Quoting JetMech (Reply 34):
I agree that no useful power is being delivered for the purposes of propelling an airframe / engine combination, but the amount of work being done on the air going through the engine is immense.

Firsly, I appologize for dumbing down the discussion, but I'm still a bit hung up on one thing.

The above quotes seem to suggest that the amount of work done by a jet engine is determined by the amount of thrust (air shoved rearwards) over a given time. So regardless of whether or not the airframe's parking brakes are applied during a full-power runup, the engine is still developing power/doing work. Whether or not it's "usefull" to the airframe seems irrelevant to me as far as calculating the engine's power. Whether the airframe that the engine is attatched to is standing still or cruising at M .80, it's still forcing loads of air backwards. Why then is the airframe's velocity a viable factor in a jet engine's power output?
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Wed Dec 06, 2006 9:12 pm

Quoting Speedracer1407 (Reply 39):
Why then is the airframe's velocity a viable factor in a jet engine's power output?

Don't hit me as I jump in, but as I understand the answers above pure thrust is not enough. To get a measure of the "power" of an engine you need to get an idea about what work it can actually do. The GE-90 may throw a lot of air backwards. However, the engines on the SR-71 throw less air backwards faster. In order to compare the two, thrust is not enough.

I hope I got that right. Otherwise, glad to have confused someone. Big grin
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jetmech
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Wed Dec 06, 2006 9:23 pm

Quoting Speedracer1407 (Reply 39):Whether or not it's "usefull" to the airframe seems irrelevant to me as far as calculating the engine's power. Whether the airframe that the engine is attatched to is standing still or cruising at M .80, it's still forcing loads of air backwards. Why then is the airframe's velocity a viable factor in a jet engine's power output?

G'day Speedracer  ,

This was the exact distinction I noted in my earlier post. When an aircraft is moving at a constant velocity under a certain set of atmospheric conditions, there will be a retarding force on the airframe which we know as drag. The engines must supply an equal amount of force in the opposite direction to maintain this constant velocity.

Purely going off my intuitive understanding, work is defined as applying a force (N or lbf) over a certain displacement (m or ft) (with the magnitude of the component of the force parallel to the direction of displacement that matters). This work (Nm or ft lb) requires a certain amount of energy to perform, and provided you can somehow keep the force same, the amount of energy consumed to perform a given amount of work will be the same whether you complete the given displacement over 1 day or 1 minute.

Applying a force of 1N over a distance of 1m (assuming the force vector is parallel to, and in the same direction as displacement) means you have done 1Nm of work. This requires you to consume energy, with 1Nm of work requiring the consumption of 1 Joule of energy to perform.

Power comes into the equation when you want to do a given amount of work in a certain time period. 1Nm of work requires the expenditure of 1 joule of energy regardless of the time taken to do the work. If you want the work done in 1 second, you must consume energy at the rate (power) of 1Nm / s, which is defined as 1 watt of power. If you want to do 1Nm of work within 1/10th of a second, you must consume energy at the rate of 10Nm / s, which is 10 watts of power.

You can see that the units of power is made of two smaller units multiplied together, namely N, which is a force, and m/s, which is velocity. Thus, for an aircraft under steady state, forward flight conditions, there will be a resistive force (N) known as drag, which will be the result of travelling at a certain velocity (m/s). Combining these units together gives the resistive "drag power" of the airframe / engine combination. The engines must supply "propulsive power" of the same magnitude and opposite sense to maintain the current airframe / engine combination velocity.

This was proposed as a method of defining the most powerful engine, but as I mentioned earlier, although such a method is based on the useful power delivered to an airframe, it relies heavily on the velocity of the airframe / engine combination, which can thus make an ultralight more "powerful" than a B773ER.

I like yourself am not too sure that this definition is in the intended "spirit" of the meaning of the word powerful for this thread. I am much more comfortable with the static thrust output definition for power, which from other posters, seems to be the set of conditions where maximum thrust is generated.

Thus, my vote for the most powerful air-breathing aircraft engine (under static conditions) still goes to the GE90-115B  

Quoting Starlionblue (Reply 40):
The GE-90 may throw a lot of air backwards. However, the engines on the SR-71 throw less air backwards faster.

I agree and disgree with this statement. One of the formulas I am familiar with for thrust is this; Thrust = [mdot * (Vin - Vex)], where for metric units, trust is in Newtons, mdot in kg / sec, and Vin and Vex are the engine inlet and exhaust velocities respectively in m/s.

This takes into account both the mass flow (amount of air throw) and the velocity change imparted on this air by the engine (how hard it throws the air). Thus a rocket, which imparts a very large velocity change to a small mass of fluid can have the same thrust as a propeller, which imparts a mild velocity change to a much larger mass of air.

The kinetic energy given to a mass (such as air) is given by KE (Joules) = 0.5 *mass (kg)*[velocity (m / s)^2]. Because of the velocity squared term, a rocket (or SR-71 engine) may need to use much more energy to generate the same amount of thrust as a propeller (or GE-90). This may also manifest as a greater rate of energy consumption, making the rocket more powerful for the same thrust if we define power as the rate of energy consumption.

Thus, it is always most efficient to generate thrust by giving the smallest velocity change to the greatest mass of fluid as possible. I think the reason we do not see a multitude of propellers powering the space shuttle is I believe that you exhaust velocity must exceed your vehicle velocity for positive thrust to be generated  Confused.
 
Regards, JetMech

[Edited 2006-12-06 13:41:47]
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Starlionblue
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Wed Dec 06, 2006 9:53 pm

Quoting JetMech (Reply 41):
Thus, it is always most efficient to generate thrust by giving the smallest velocity change to the greatest mass of fluid as possible. I think the reason we do not see a multitude of propellers powering the space shuttle is I believe that you exhaust velocity must exceed your vehicle velocity for positive thrust to be generated

Indeed. And there's the small fact that propellers are not reaction devices. They need a fluid to work in. Might be hard once you leave the atmosphere.  Wink
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jetmech
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Wed Dec 06, 2006 10:13 pm

Quoting Starlionblue (Reply 42):
They need a fluid to work in.

Erm.... Yes; I completely forgot to make mention of that small problem  blush  bigthumbsup !
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RE: Most Powerful Aircraft Powerplant Ever Designe

Wed Dec 06, 2006 11:41 pm

You can make a prop or pure turbine airbreather first stage with a short lifespan. The second stage would be powered traditional rocket(s). This would make the launcher much lighter since the first stage wouldn't have to carry oxygen. I believe the problem lies in the lower specific impulse compared to pure rocket propulsion, and the complexity. That is, rockets are simpler and still weigh less.
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Thu Dec 07, 2006 1:35 am

With apologies for getting the detail wrong in advance, the general principles of the jet are to generate thrust by changing the momentum of the gas passing through it. The engine can either accelerate a litle bit of air a lot, or a lot of air a little bit. The straight-pipe turbojet (e.g. J79 in the Phantom) is an example of the former, and the latter goes through the bypass jets to propellor aircraft.
The relative merits are that accelerating a lot of air a little bit involves a small change in energy, accelerating a little bit a lot involves a large change. The change of energy is reflected in fuel burn. Hence the turboprop is very efficient, the J79 isn't, for generating the same specific thrust. However, the propulsive efficiency of a jet is related to the relative jet velocity and so as the airframe speed increases, the propulsive efficiency of the proplellor drops off (regardless of supersonic tip losses). The straight pipe turbojet improves as forward speed increases to a point), however, so that at c. 600 m.p.h. (it says here in the RR Jet Engine book), the high bypass engine has a higher propulsive efficiency that a prop at 400mph, and the straight-pipe turbojet betters the prop by c. 900mph.
The bottom line is that the high bypass engines are efficient at 600mph but thrst drops off both with height (as aready noted in the thread) but also with forward speed as the relative jet velocity drops, whereas the straight-pipes are less efficient at lower speeds, but improve as the aircraft velocity increases.
The GE90 therefore may not be that powerful at 600mph to a J58 (perhaps, I don't know the real numbers), and the J58 generate far more thrust than the GE90 at supersonic speeds (hypotherical situation).
Incidentally on this issue, the Phantom was fitted with J79's except for those used in the UK, fitted with RR Speys. The Spey is more powerful than the J79, but the UK Phantom is always quoted as being the slowest, heaviest Phantom. Talking to the Phantom jocks though, they will tell you that a Spey-powered Phantom at M0.9 will leave a J79 Phantom standing because as a bypass engine, it has better propulsive efficiency at that speed, whereas it's propulsive efficiency drops off more quickly with speed to make it the slower aircraft for outright speed. As most combat takes place around M0.9, then guess which they prefer?
As another point on thrust vs. power, the Industrial Trent generates 58MW in electricity, which equates to around 78,000hp. Take into account that this is a continuous setting, not a peak rating, and the losses in the generator are not negligible, we could safely deduce powers in excess of 90,000 hp from the fan shaft for this engine on take-off. The GE90 will be above this.
 
sprout5199
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Thu Dec 07, 2006 11:42 am

Quoting Xv408 (Reply 45):
As another point on thrust vs. power, the Industrial Trent generates 58MW in electricity, which equates to around 78,000hp. Take into account that this is a continuous setting, not a peak rating, and the losses in the generator are not negligible, we could safely deduce powers in excess of 90,000 hp from the fan shaft for this engine on take-off. The GE90 will be above this

So:"Tory-IIC" was run for five minutes at full power, producing 513 megawatts .

If 58MW = 78,000hp then 513MW= about 750,000hp.(que the 1.21 gigawatts from Back to the Future) So I guess I win. The Tory-11C is the most powerful aircraft power plant ever designed.  Wow!

If you ever hear that engine, its a killer sound.


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speedracer1407
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Thu Dec 07, 2006 3:59 pm

Quoting JetMech (Reply 41):
Purely going off my intuitive understanding, work is defined as applying a force (N or lbf) over a certain displacement (m or ft) (with the magnitude of the component of the force parallel to the direction of displacement that matters). This work (Nm or ft lb) requires a certain amount of energy to perform, and provided you can somehow keep the force same, the amount of energy consumed to perform a given amount of work will be the same whether you complete the given displacement over 1 day or 1 minute.

Applying a force of 1N over a distance of 1m (assuming the force vector is parallel to, and in the same direction as displacement) means you have done 1Nm of work. This requires you to consume energy, with 1Nm of work requiring the consumption of 1 Joule of energy to perform.

Power comes into the equation when you want to do a given amount of work in a certain time period. 1Nm of work requires the expenditure of 1 joule of energy regardless of the time taken to do the work. If you want the work done in 1 second, you must consume energy at the rate (power) of 1Nm / s, which is defined as 1 watt of power. If you want to do 1Nm of work within 1/10th of a second, you must consume energy at the rate of 10Nm / s, which is 10 watts of power.

Thanks, JetMech for your excellent explaination. I think my fundamental problem was using work and power interchangeably.
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jetmech
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Thu Dec 07, 2006 5:01 pm

Quoting Sprout5199 (Reply 46):
So:"Tory-IIC" was run for five minutes at full power, producing 513 megawatts

G'day Sprout5199  Smile,

Wikipedia states that the actual thrust output of the Tory-IIC is approximately 35,000 lbf (156kN). I believe that the Tory-IIC was a ramjet that utilised the power from a nuclear reactor to heat and expand air instead of using a chemical reaction with a fuel as is done in many conventional ramjets.

I thus think that the 513Mw is referring to the power of the nuclear reactor, not the equivalent thrust horsepower of the device. I would presume that being a ramjet, the velocity of the air through the device would be fantastic. To produce 35,000 lbf of thrust at ramjet type speeds would require a very rapid rate of heating of the air, hence the need for such a powerful nuclear reactor  Confused .

If we consider powerful to mean the consumption rate of energy of a motor alone, regardless of what is done with this power, then I am quite sure that the Tory-IIC would be without peer, but the device may need to take a back seat if power is considered to be maximum static thrust.

Regards, JetMech
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sprout5199
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RE: Most Powerful Aircraft Powerplant Ever Designed?

Thu Dec 07, 2006 10:26 pm

Howdy JetMech,

Quoting JetMech (Reply 48):
but the device may need to take a back seat if power is considered to be maximum static thrust.

So true. Can you get static thrust from a ramjet? I remember seeing a show about the Tory-II on History or Discovery channel. They used all the oil well drill casings in California to have a tank big enough to hold the high pressure air to run the engine. Then they had to heat the air to something like 1000 degrees F to simulate air moving that fast. used a million 1 inch steel ball bearings to hold th heat so the air could pass through. Was a very interesting show. What they did in the 50's and 60's with slide rules and active minds just boggles my mind. To even think you could make a nuclear powered missile do Mach 3 at sea level took some balls. and then to build the engine for it and make it work!!! Oh to be an Mech. Engineer back then(hell, even a gopher for an engineer)

Dan in Jupiter

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