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Faro
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Most Influential Jet Engine Design?

Sun Apr 03, 2011 9:40 am

Based on lasting influence on the development of jet engines, what in you opinion was the most influential jet engine? My guess would be either the J57 -judging by the number of highly successful derivative designs- or the Conway, the first turbofan (all big fans are just an extension of that idea). Any thoughts?

Faro
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Pihero
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RE: Most Influential Jet Engine Design?

Sun Apr 03, 2011 11:18 am

I think that the invention of the axial flow compressor is what made everything happen.
In this respect, kudos to Dr Frantz Anselm and the Junkers Motoren firm (Ju Mo was the name for all operational german engines, including the Messerschmitt 262 ).
It took western countries another ten years before they could fly an axial flow jet engine of their own.
The rest is history.
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A342
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RE: Most Influential Jet Engine Design?

Sun Apr 03, 2011 3:59 pm

Quoting Pihero (Reply 1):
Ju Mo was the name for all operational german engines, including the Messerschmitt 262

Actually, some Ar 234s and He 162s used the BMW 003 (if you want to call the He 162 an operational aircraft).
Exceptions confirm the rule.
 
baroque
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RE: Most Influential Jet Engine Design?

Sun Apr 03, 2011 4:13 pm

Quoting Pihero (Reply 1):
I think that the invention of the axial flow compressor is what made everything happen.
In this respect, kudos to Dr Frantz Anselm and the Junkers Motoren firm (Ju Mo was the name for all operational german engines, including the Messerschmitt 262 ).
It took western countries another ten years before they could fly an axial flow jet engine of their own.

Well it was not ignorance, it was reliability that kept the UK on centrifugal engines even thought axial flow engines had been proposed earlier than the centrifugal flow engines.

From Wiki on the Axial flow Metrovick F 2

Alan Arnold Griffith published a seminal paper in 1926, An Aerodynamic Theory of Turbine Design, that for the first time clearly demonstrated that a gas turbine could be used as a practical, and even desirable, aircraft powerplant. The paper started by demonstrating that existing axial compressor designs were "flying stalled" due to their use of flat blades, and that dramatic improvements could be made by using airfoil designs instead, improvements that made a gas turbine practical. It went on to outline a complete compressor and turbine design, using the extra exhaust power to drive a second turbine that would power a propellor. In today's terminology the design was a turboprop. In order to prove the design, Griffith and several other engineers at the Royal Aircraft Establishment built a testbed example of the compressor in 1928 known as Anne, the machinery being built for them by Fraser and Chalmers. After Anne's successful testing they planned to follow this up with a complete engine known as Betty.

In 1929 Frank Whittle's thesis on pure jet engines was published, and sent to Griffith for comment. After pointing out an error in Whittle's mathematics, he went on to deride the entire concept, saying that the centrifugal compressor he used would be impractical for aircraft use due to its large frontal area, and that the use of the jet exhaust directly for power would be extremely inefficient. Whittle was distraught, but was convinced that he should patent the idea anyway. Five years later a group of investors persuaded him to start work on what would be the first working British jet engine.


So perhaps even more kudos to Anne and Betty!!! Griffith was convinced for a long time that reaction jets would not work, but he thought that turbo-props would work just fine and so it is not surprising that RR were early into bypass jets with the Conway. But trying to fit it in the wing gave them low ambitions for the BPR unfortunately.

While the BMW axial flow units were in service early, they were not very serviceable compared with the Whittle derived Rollers. They were also about 30% less efficient according to Whittle based on post war testing. SFC of about 1.3 compared wtih close to 1 for the Whittle based engines.
 
Northwest727
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RE: Most Influential Jet Engine Design?

Sun Apr 03, 2011 5:08 pm

Would you consider the transition from the early combustion chamber "cans" to the modern, "annular" combustion chamber design somewhat influential?

Though not quite as influential (but still so nonetheless), is the high bypass turbofan, wide chord blades, low emissions combustion chambers, and the nacelles themselves (from the early noisy sucker doors and short fan bypass ducts to today's acoustic panel-lined "quiet nacelles").

For the military and supersonic flight side of things, I think the afterburner (reheat) and the variable-geometry intake are pretty significant.
 
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RE: Most Influential Jet Engine Design?

Mon Apr 04, 2011 4:41 am

Quoting Northwest727 (Reply 4):


Though not quite as influential (but still so nonetheless), is the high bypass turbofan,

I think the high-BP is up there with the annular combustor. Every transport turbofan developed since the first HBPR engines has been HBPR and higher and higher...
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C46
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RE: Most Influential Jet Engine Design?

Mon Apr 04, 2011 7:30 am

Not a single answer but I would go with the engine derivatives progressing from the Lockheed C-5 program: the TF-39 (CF6 derivatives) and the JT9D (derived from Pratt and Whitney’s entry into the C-5 engine competition – forgot what that was called).

These both paved the way to the hi-bypass turbofans used today. I used to work on the C-5 (TF-39 back then) so when I first seen the GE90 come out, it was without doubt to me an amazing feat of engineering based on decades of advancement. It’s like a fine wine and I appreciate it more as I get older.
 
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Faro
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RE: Most Influential Jet Engine Design?

Mon Apr 04, 2011 7:50 am

Quoting Pihero (Reply 1):
It took western countries another ten years before they could fly an axial flow jet engine of their own.

Ten years to catch up on the German design? Why so long, what is it that makes axials so much more complicated than centrifugals?

Faro
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C46
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RE: Most Influential Jet Engine Design?

Mon Apr 04, 2011 8:03 am

Quoting faro (Reply 7):
what is it that makes axials so much more complicated than centrifugals?

Hi Faro - because the axial design has individual stages (rotors and stators) whereas the centrifugal design is one big impeller (stage). Think of multiple sections (axial) vs. the classic washing machine agitator (centrifugal)   Inherently more complex, especially from a manufacturing aspect.
 
baroque
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RE: Most Influential Jet Engine Design?

Mon Apr 04, 2011 3:52 pm

Quoting C46 (Reply 8):
Hi Faro - because the axial design has individual stages (rotors and stators) whereas the centrifugal design is one big impeller (stage). Think of multiple sections (axial) vs. the classic washing machine agitator (centrifugal) Inherently more complex, especially from a manufacturing aspect.

That in part, but much more because in the early days they got better efficiency and reliability from the centrifugal first stage.

And as I commented, look at the Derwent SFC against the BMW axial SFC. 30% is quite a bit!

But the axial flow compressor was the aim. The Sapphire - first run in 1948 - stemmed from an engine started in 1940. In the meantime, the centrifugal engines provided effective solutions faster and more reliably. But I think they always knew that axial flow would be the way to go.
 
wingscrubber
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RE: Most Influential Jet Engine Design?

Mon Apr 04, 2011 7:08 pm

Aside from which specific engine was 'most influential', this website has some nice engine illustrations:
http://www.aircraftenginedesign.com/index.html
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Jetlagged
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RE: Most Influential Jet Engine Design?

Mon Apr 04, 2011 7:55 pm

Quoting C46 (Reply 6):
Not a single answer but I would go with the engine derivatives progressing from the Lockheed C-5 program: the TF-39 (CF6 derivatives) and the JT9D (derived from Pratt and Whitney’s entry into the C-5 engine competition – forgot what that was called).

I was thinking the same thing. These engines changed the commercial aviation industry completely.
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Pihero
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RE: Most Influential Jet Engine Design?

Tue Apr 05, 2011 10:17 am

Quoting Baroque (Reply 9):
But the axial flow compressor was the aim. The Sapphire - first run in 1948 - stemmed from an engine started in 1940. In the meantime, the centrifugal engines provided effective solutions faster and more reliably. But I think they always knew that axial flow would be the way to go.

So true;;; but they knew size alone would require axial flow compressors.
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Faro
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RE: Most Influential Jet Engine Design?

Fri Apr 08, 2011 8:44 am

Out of curiousity, which was the first engine to incorporate hollow, air-cooled turbine blades? That's quite a metallurgical tour de force; who was behind this innovation?

Faro
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26point2
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RE: Most Influential Jet Engine Design?

Fri Apr 08, 2011 2:19 pm

Don't forget the TFE 731

It was the first successful Turbo Fan for the bizjet set. Helped Learjet, Hawker, Falcon, IAI, and others maximize the potential of their products.
 
rwessel
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RE: Most Influential Jet Engine Design?

Fri Apr 15, 2011 7:40 am

Quoting faro (Reply 7):
what is it that makes axials so much more complicated than centrifugals?

Each axial stage raises the pressure only a small amount, which means you need a fair number of stages to raise the pressure enough to run the engine, and thus lots of blades, and the complex assemblies that go with that. And then you need a stator stage for each compressors stage. Worse, the aerodynamics are much touchier, since even a small amount of leakage back past the axial stage will significantly reduce (or eliminate) the effectiveness of the axial stage.

A centrifugal stage will have a much higher pressure rise, and is usually made from a single piece of material (although not always, but even then the blades are mounted on their long edges to the disk, which is rather simpler). And a bit of backflow leakage is much less significant. You also need a less complex set of stators, as there's less "swirl" introduced, and much of what is, is naturally straightened out by the big bend after the (centrifugal) compressor stage.

Many smaller turbines still use centrifugal compressors. Again aerodynamics factors into that - smaller compressors have more difficult aerodynamics, since the main area where backflow happens is around the edge of the turbine disk, and that's proportionately larger on a smaller disk. Some smaller turbines have two, sometimes back-to-back, centrifugal compressors, and some combine a few axial stages with a centrifugal stage.

For large engines, the increased efficiencies of axial compressors, along with the decreasing backflow issues, makes axial designs pretty universal.

Some secondary considerations come into play too - centrifugal compressors tend to make for shorter engines, but rather fat ones. Also centrifugal compressors tend to be much more rugged than axial ones, and ice/FOD ingestion issues may lead to a preference for the former.
 
travelavnut
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RE: Most Influential Jet Engine Design?

Fri Apr 15, 2011 10:03 am

Excuse my ignorance, but can somebody explain in layman terms the difference between axial- and centrifugal flow? I think I get the basic (lots of stages vs. only a few), but I'm having a hard time visualising the centrifugal stages.
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travelavnut
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RE: Most Influential Jet Engine Design?

Fri Apr 15, 2011 10:52 am

Through the magic of Google I answered my own question;

http://ffden-2.phys.uaf.edu/212_fall...003.web.dir/Erik_Weflen/Page4.html

 
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RE: Most Influential Jet Engine Design?

Fri Apr 15, 2011 9:24 pm

From my outsider's point of view, I would say the JT-3 engine family, which allowed the start of (relatively) mass transportation on jet aircraft, and then, when fitted with fans, opened the road to quietness and economy. It was just the beginning of the paradigm change that moved pure jets away from air transportation.
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RE: Most Influential Jet Engine Design?

Mon Apr 18, 2011 6:07 pm

Quoting faro (Reply 13):
Out of curiousity, which was the first engine to incorporate hollow, air-cooled turbine blades? That's quite a metallurgical tour de force; who was behind this innovation?
http://www.patentgenius.com/patent/4664597.html
http://www.freepatentsonline.com/5193980.pdf

I did some searching - seems that's quite a tough question to answer. There's prior art listed for recent patents going all the way back to 1949 covering 'coolant passages' for turbine blades, but looking at the prior art referenced in the second 1993 patent, it seemed to gain traction in the 60s with IP attributed to Snecma, GE & United Technologies.

I wonder how the other engine makers get around this IP-battleground, I bet a lot of patent licensing goes on.
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jetlife2
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RE: Most Influential Jet Engine Design?

Wed Apr 20, 2011 11:19 pm

Quoting faro (Reply 13):
Out of curiousity, which was the first engine to incorporate hollow, air-cooled turbine blades? That's quite a metallurgical tour de force; who was behind this innovation?

Faro

Well I am not sure of the definitive answer. But the Jumo 004B (ME262) had cooled HPT blades as can be clearly seen in the example on display at the Wright-Patterson museum. If you read the wikipedia entry it describes it in quite some detail.

Being somewhat of an engine guy   when I first saw this engine in Wright-Pat, my jaw literally dropped. Axial flow compressor and cooled single stage HPT, 1943! Are you kidding me!

Back to the original question, I would think you would have to include the RR Pegasus in this list, as the engine enables the entire design philosophy of the aircraft in a unique way.

The J79 made high ground with variable stators and a new mark in thrust to weight...

I think the F101 should also be included, as the core begat the CFM56, the F110, the F117...truly influential.

Cheers

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baroque
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RE: Most Influential Jet Engine Design?

Thu Apr 21, 2011 6:19 am

Quoting jetlife2 (Reply 20):
include the RR Pegasus

Might be appropriate to mention that the Pegasus comes from the Bristol part of RR and was designed under Bristol Siddeley's Technical Director Stanley Hooker. In turn that design goes back to a concept from Michel Wibault, a French aircraft designer.

http://en.wikipedia.org/wiki/Rolls-Royce_Pegasus
All that gets us close to the Olympus, the first two spool engine and remarkable for a number of other reasons especially allowing Concorde to supercruise.
 
Pihero
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RE: Most Influential Jet Engine Design?

Thu Apr 21, 2011 9:04 am

Quoting Baroque (Reply 21):
All that gets us close to the Olympus, the first two spool engine and remarkable for a number of other reasons especially allowing Concorde to supercruise.

Yes !
I've always laughed at the much vaunted "supercruise" qualities of the F-22 and the F-35 . The Olympus did it forty years ago.
For an engine which was first run in 1950, more than sixty years ago, which saw an increase of the original thrust by some mere 400 % and is still in production (for naval engines), Baroque you have found the most influential engine jet design of all times.
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baroque
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RE: Most Influential Jet Engine Design?

Thu Apr 21, 2011 2:25 pm

Quoting Pihero (Reply 22):
For an engine which was first run in 1950, more than sixty years ago, which saw an increase of the original thrust by some mere 400 % and is still in production (for naval engines) .......... have found the most influential engine jet design of all times.

Yes, well this did cross my mind when the thread was first posted. There was the first rush of designs with Whittle usually getting the nod ahead of Ohain but really Griffith was ahead of both except he did not happen to believe (at that stage) in reaction propulsion. Then there was the post war flush of designs and improvements but two spools was the key to turbofans/bypass engines.

Once the turbofans arrived, aside from 3 spool v 2 spool and size the changes have generally been smaller even if taken over 50 years the collective changes from first to the latest are astonishing, but they have been gradual.

On what it actually did, the Olympus was pretty amazing, but a lot of what it did was after its parent was taken over by the all consuming (as far as UK engine manufacturers were concerned) RR. And while I don't know the details, one can assume poor old Bristol located out in the wild west of, well Bristol, would have had pretty much the raw end of most of the prawns going around. Or in other words RR was going to favour its own children ahead of the step child, however formidable the interloper happened to be.

Back to Griff, from Wiki
In 1926 he published a seminal paper, An Aerodynamic Theory of Turbine Design. He demonstrated that the woeful performance of existing turbines was due to a flaw in their design which meant the blades were "flying stalled", and proposed a modern airfoil shape for the blades that would dramatically improve their performance. The paper went on to describe an engine using an axial compressor and two-stage turbine, the first stage driving the compressor, the second a power-take-off shaft that would be used to power a propeller. This early design was a forerunner of the turboprop engine. As a result of the paper, the Aeronautical Research Committee supported a small-scale experiment with a single-stage axial compressor and single-stage axial turbine. Work was completed in 1928 with a working testbed design, and from this a series of designs was built to test various concepts.
AND
After a short period Whittle's work at Power Jets started to make major progress and Griffith was forced to re-evaluate his stance on using the jet directly for propulsion. A quick redesign in early 1940 resulted in the Metrovick F.2, which ran for the first time later that year. The F.2 was ready for flight tests in 1943 with a thrust of 2,150 lbf, and flew as replacement engines on a Gloster Meteor, the F.2/40 in November. The smaller engine resulted in a design that looked considerably more like the Me 262, and had improved performance. Nevertheless the engine was considered too complex, and not put into production.

Griffith's original rejection of Whittle's concepts has long been commented on. It certainly set back development of the jet engine in England. His motivations have long been the topic of curiosity, with many people suggesting that his endless quest for perfectionism was the main reason he didn't like Whittle's "ugly" little engine, or perhaps the belief that "his" design was innately superior.

NOT TO MENTION
Griffith joined Rolls-Royce in 1939, working there until 1960. He designed the AJ.65 axial turbojet which led to the development of the Avon engine, the company's first production axial turbojet. He then turned to the turbofan (known as "bypass" in England) design and was instrumental in introducing the Rolls-Royce Conway.
He missed out on two spool but did go to the bypass engine. So maybe Griffith should rate ahead of both Whittle and Ohain in terms of concepts, both in the sense of time - he does a good imitation of being first - and engineering design.
 
tdscanuck
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RE: Most Influential Jet Engine Design?

Thu Apr 21, 2011 2:33 pm

Quoting Pihero (Reply 22):
I've always laughed at the much vaunted "supercruise" qualities of the F-22 and the F-35 . The Olympus did it forty years ago.

Supercruise is an airframe property, not an engine property. To achieve supercruise you just need enough unagumented thrust and a supersonic exit jet. The latter is trivial and had been around long before the Olympus. Having enough unaugmented thrust is easy if you don't limit the number of engines (e.g. the Valkyrie bomber). Any engine can operate an aircraft at supercruise with the right nozzle and enough of the engines.

Supercruise on a fighter is a *huge* deal due to the impact on combat range (the same reason it's a big deal on Concorde). The trick with fighters is that you have far less room to stuff the necessary unaugmented thrust into the airframe, a problem Concorde didn't have.

Tom.
 
jetlife2
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RE: Most Influential Jet Engine Design?

Thu Apr 21, 2011 7:08 pm

Quoting Baroque (Reply 21):
Quoting jetlife2 (Reply 20):
include the RR Pegasus

Might be appropriate to mention that the Pegasus comes from the Bristol part of RR
Quoting Baroque (Reply 21):
All that gets us close to the Olympus
Quoting Baroque (Reply 23):
And while I don't know the details, one can assume poor old Bristol located out in the wild west of, well Bristol, would have had pretty much the raw end of most of the prawns going around. Or in other words RR was going to favour its own children ahead of the step child

Well I have to disclose I started my career in RR Bristol in 1978 and worked on both Pegasus and Olympus, both fine machines. Although junior at the time, there was no sense that I perceived that we got shortchanged relative to Derby. By that time Bristol was positioned as the military division and Derby commercial (Olympus being the exception because of its origins) and seemed to be appropriately funded and supported. While it was clear that Derby was HQ, there was not a sense of competition with them and I traveled there to share their resources in labs etc. Others who are still there may want to comment too...but we're a bit off topic!

Cheers

Gareth
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Acheron
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RE: Most Influential Jet Engine Design?

Thu Apr 21, 2011 7:21 pm

Quoting tdscanuck (Reply 24):
Supercruise on a fighter is a *huge* deal due to the impact on combat range (the same reason it's a big deal on Concorde). The trick with fighters is that you have far less room to stuff the necessary unaugmented thrust into the airframe, a problem Concorde didn't have.

Still shouldn't be a huge deal, considering it was a fighter jet the first one to do it. An EE Lightning to be precise.

Quoting Pihero (Reply 22):
and the F-35

The F-35 can't supercruise.
 
Pihero
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RE: Most Influential Jet Engine Design?

Thu Apr 21, 2011 8:45 pm

Quoting Acheron (Reply 26):
The F-35 can't supercruise.

Thanks.I thought it did with all the hypre around it .

Quoting Acheron (Reply 26):

Still shouldn't be a huge deal, considering it was a fighter jet the first one to do it. An EE Lightning to be precise.

Remember that, but it was then just called supersonic flight on dry thrust ?

Quoting tdscanuck (Reply 24):
To achieve supercruise you just need enough unagumented thrust and a supersonic exit jet.

I thought most turbojet engines had a supersonic exhaust, which made them bloody thirsty and unefficient at low speeds. In fact it could have been easier to design in the sixties superfast combat aircraft.
The TU-144 had fan engines, but needed reheat during cruise in order to overcome the increased drag of the front of these engines
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Jetlagged
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RE: Most Influential Jet Engine Design?

Fri Apr 22, 2011 12:05 am

Quoting Pihero (Reply 27):
I thought most turbojet engines had a supersonic exhaust, which made them bloody thirsty and unefficient at low speeds. In fact it could have been easier to design in the sixties superfast combat aircraft.

You need a supersonic nozzle to achieve supersonic exhaust velocity, i.e. a convergent-divergent nozzle. Most turbojets did not have those as they were not designed to have reheat. A reheated turbojet (or turbofan for that matter) would need a con-di nozzle and so is potentially capable of providing supercruise thrust.
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Pihero
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RE: Most Influential Jet Engine Design?

Fri Apr 22, 2011 12:53 am

Thanks, Jetlagged

I have to confess that I stopped for a few seconds on this *con-di nozzle* as I couldn't understand what Mrs Rice was doing there.

Cheers !

[Edited 2011-04-21 17:54:33]
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baroque
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RE: Most Influential Jet Engine Design?

Fri Apr 22, 2011 7:39 am

Quoting jetlife2 (Reply 25):
By that time Bristol was positioned as the military division and Derby commercial (Olympus being the exception because of its origins) and seemed to be appropriately funded and supported. While it was clear that Derby was HQ, there was not a sense of competition with them and I traveled there to share their resources in labs etc.

Thanks, I hoped I would provoke more knowledgeable comment than mine. Good to hear that. It means that RR had changed a bit from the modus operandi that Whittle writes about in his autobiography - then again, I suspect Whittle must have been quite a challenge to work with. Cannot help wondering what it would have been like in around 1966 to 1970 though.

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