Talk:Turbofan/Archive 1

Archive 1

Please explain

Please explain why the following sentence noted in part was removed from the triple spool paragraph in the article. Thank you.

"Because the RB211/Trent designs have a higher IPC pressure rise than the American engines, the HPC pressure rise is less resulting in a shorter, heavier engine". — Preceding unsigned comment added by Solarsail (talk • contribs) 23:54, 27 April 2011 (UTC)

Your question, and my answer, are at the bottom of the page. Look down there. Dolphin (t) 00:00, 28 April 2011 (UTC)

Lack of Sources

Much of this article contains facts that really need sources to support... like in the introduction the statement that turbofans are more efficient than turbojets up to Mach 1.6. That kind of claim is something that definitely needs a source. SidewinderX (talk) 00:42, 22 September 2008 (UTC)

Incorrect information

low bypass engines have low specific thrust and high bypass engines have high specific thrust.

Do you have a reference for that? The specific thrust is the thrust relative to the airflow- but high bypass engines have a large airflow but expel it at relatively low speeds, and hence you would expect high bypass engines to have a low specific thrust.- (User) Wolfkeeper (Talk) 15:25, 26 October 2008 (UTC)

If u want proof of this check out Basics of Aerospace Propulsion by K. Srinivas. 2008. The abstract of reference 3 begins with the statements: “Thermal efficiency of gas turbines is critically dependent on temperature at the turbine inlet; the higher this temperature, the higher the efficiency. Stoichiometric combustion would provide maximum efficiency”. This view about gas turbine efficiency is widely spread, however, it is incorrect. In reference 1 it is shown that when gas properties are modeled accurately the variation of cycle efficiency with turbine inlet temperature at constant pressure ratio exhibits a maximum at temperatures well below the stoichiometric limit.[1] —Preceding unsigned comment added by 122.106.203.197 (talk • contribs) 09:14, 26 October 2008 (UTC)

The triple spool design is a heavier engine than the twin spool. Established Data noted below proves this point. After reviewing the data below please change the word to "heavier" in the following sentence below...."Because the RB211/Trent designs have a higher IPC pressure rise than the American engines, the HPC pressure rise is less resulting in a shorter, lighter "should read heavier engine".

Thanks in advance for the correction.

Engine Weight Comparisons for engines with similar thrust.Italic text

http://easa.europa.eu/certification/...700_series_engines-01-06032006.pdf GE: CF6-80E1 Dry Weight: 5,091.62 kgs. (11,225 lbs). Includes all basic engine accessories and optional equipment as listed in the manufacturer’s engine specs. http://easa.europa.eu/certification/...1-14062004.pdf

RR: T700 series. Dry Weight: 6,160 kgs. (13,580 lbs). (Not including fluids and Nacelle EBU) http://easa.europa.eu/certification/...1-06032006.pdf

A330-200 O.E.W. weights for each applicable engine.Italic text

http://www.airbus.com/fileadmin/media_gallery/files/tech_data/AC/Airbus_AC_A330_Jan11.pdf GE powered O.E.W. - 119,831kgs. RR powered O.E.W. - 119,931kgs.

Engines applicable to the A330-300Italic text http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/3c27fd7504a36b648625760e0046cb5a/$FILE/E36NE.pdf

PW 4168 weighs 12,900 lbs.- 5,863 kgs.

Weight of basic engine includes all essential accessories, but excludes starter, exhaust nozzle, and power source for the ignition system.

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/d69e8a472455be9286257495006282e5/$FILE/E39NE.pdf

RR Trent 772B-60 dry powerplant weighs 14,360 lbs.- 6,527 kgs.

Engines applicable to the B747-400Italic text

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/a54a5cdbed477da18625753c004dd282/$FILE/E24NE.pdf PW 4062 weighs 9,420 lbs. - 4,273 kgs. Weight of basic engine includes all essential accessories, but excludes starter, exhaust nozzle, and power source for the ignition system.

http://rgl.faa.gov/Regulatory_and_Guidance_library/rgMakeModel.nsf/0/706579a7e83efab48625727b00751aff/$FILE/E13NE.pdf CF6-80C2B5F weighs 9,790 lbs. - 4,441 kgs. Weight includes basic engine accessories & optional equipment as listed in the engine manufacturer's specifications, including condition monitoring instrumentation sensors.

http://www.caa.co.uk/docs/1419/SRG_PRO_1048%20iss11.pdf RB211-524H2-T-19 weighs 12,573 lbs. - 5,703 kgs. Dry powerplant weight less intake, intake systems, cowl doors and cowl door support structure.

Engines applicable to the B767-300ERItalic text

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/a54a5cdbed477da18625753c004dd282/$FILE/E24NE.pdf PW 4056 weighs 9420 lbs. - 4,273 kgs. Weight of basic engine includes all essential accessories, but excludes starter, exhaust nozzle, and power source for the ignition system.

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/b015c4c8fa2760a18625765c0053b800/$FILE/E13NE.pdf CF6-80C2B2 weighs 9670 lbs.- 4,395 kgs. Weight includes basic engine accessories & optional equipment as listed in the manufacturer's engine specifications, including condition monitoring instrumentation sensors.

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/78635932a4cb7e7b862572a70057e006/$FILE/E30NE.pdf RB211-524H-T-36 weighs 12,540 lbs.- 5,700 kgs. Dry powerplant weight less intake, intake systems, cowl doors, and cowl door support structure.

Engines applicable to the B757-200 / -300Italic text

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/4e1d135907e0ce8686256df1005b1233/$FILE/E17NE.pdf PW 2043 weighs 7,300 lbs. - 3,318kgs.

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/1aaba05dd1012e30862574950062f87e/$FILE/E12EU.pdf RB211-535E4-B-37 weighs 7,603 lbs. - 3,456 kgs. —Preceding unsigned comment added by 50.92.115.223 (talk) 21:02, 17 April 2011 (UTC)

Manufacturer joint ventures

I suggest the manufacturer section be revised in order to account for joint ventures. In particular, the IAE V2500 is as much a Pratt product as it is a Rolls product. Marimvibe 06:27, 12 November 2006 (UTC)

Useful link for GTF

I am not sure how to incorporate this link into the article:("Airbus rethinks plan to put winglets on A320". Kingsley-Jones, M. Flight International. October 10, 2006.) Do we have a turbine expert on hand? —Joseph/N328KF (Talk) 16:43, 12 January 2007 (UTC)

Noob friendly video

http://video.google.com/videoplay?docid=6519732916557390910&q=turbofan&hl=en

Inaccurate Picture Caption

The caption for the picture of the intake duct on the A7 Corsair states that the decreasing diameter of the duct slows the air entering the engine. I understand that intake air velocity must be decreased but this would not be accomplished my decreasing the intake diameter. Decreasing that diameter would actually increase the velocity by Bernoulli's equation. There is clearly something else causing the airspeed reduction that is not shown in the picture. I suggest that this picture be removed or the caption changed to eliminate this confusion. Any thoughts?

I came to the same conclusion myself. --Dan Griscom (talk) 02:21, 21 May 2008 (UTC)

Yeah, actually it looks to me like the duct gets bigger- that would slow the air for a subsonic aircraft.- (User) WolfKeeper (Talk) 03:38, 21 May 2008 (UTC)

I changed the picture to one of an Alphajet in which the increase of the inlet diameter prior to the Compressor fan is more apparent:Dreidecker (talk) 09:08, 16 November 2008 (UTC)

Spoolup sounds on newer turbofans

Has anyone noticed that on turbofans built since the 1980s, the noise increases dramatically during spoolup, but drops somewhat when the desired RPM is reached? Any idea what causes this and why older turbofans didn't do this? I've noticed it on the 757 and newer 737s; not so much the MD-80s. -Rolypolyman (talk) 02:40, 31 January 2008 (UTC)

The noise you're hearing, generally of a low rumbling quality, is present on all turbine engines during startup, and during other periods of acceleration. It takes a bunch of fuel burning to get a turbine engine up to idle speed, in addition to the power of the starter cranking. Once the engine stabilizes at idle speed the fuel flow generally goes down, because it takes less fuel to maintain idle than it does to reach idle. If you're noticing it more on newer aircraft, it's probably because for one the engines are larger, and secondly they're generally high-bypass types. High bypass engines have a lot more weight in the fan assembly and the entire N1 spool, so it takes a lot of power to get them up to idle speed. Shreditor (talk) 10:16, 20 August 2008 (UTC)

Article way too technical

I'd like to suggest that writers/editors with jet engine knowledge and general (not technical) writing experience consider reworking this article to retain an encylcopedic/general audience tone. The article is way too technical and would certainly lose a general audience in its arcane and technical use of language, mathematical formulae, etc.

It is common for persons highly knowledgeable in a specific field or area to not write in a general, user-friendly style; the temptation is often to explain a subject as if discussing that subject with colleagues who are already knowledgeable in the particular area of expertise; in essence, to "talk down" to an audience. Viewed from another standpoint, the emphasis here should focus on the creation of an instructive article---as if one were teaching a high school class of pupils who have never heard of a turbofan engine, or a high pressure compressor, etc. I believe that would be in keeping with the best philosophy of Wikipedia. (Ronsword (talk) 22:35, 1 September 2008 (UTC))

I'm not sure what level this or any other article in the wikipedia should be aimed at, and there don't seem to be any relevant policies or guidelines on this. This is an article on a particular sort of jet engine, which are not noted for their simplicity, and it is not the simplest type of jet engine either. It's always most important to consider your audience, and this is a technical engineering subject, and I'm actually not sure what a general audience wants from this article. FWIW I compared this to NASA's article[2], and frankly I'm not sure that's much better.- (User) WolfKeeper (Talk) 23:04, 1 September 2008 (UTC)

However, the introduction should be broadly understandable at least. Do you find the introduction is reasonable?- (User) WolfKeeper (Talk) 23:04, 1 September 2008 (UTC)

The prologue, through the intro (up until "After World War II, 2-spool (or 2-shaft) turbojets...") is fine, but might be better if extended, in keeping with the Wiki guidelines which suggest putting the most accessible areas of the article's subject matter up front. The guidelines also suggest limiting technical "jargon", using more pictures, and less mathematical symbols or formulae which might not be understood by many readers.

One suggestion for the intro might be to explain the basic functions of a turbofan, a brief history of its design and departure from a turbojet, the advantages of bypass (in the most general terms), a brief outline of its function (from air intake to compression, to combustion and then to exhaust), a brief description of the main components involved (stators, fan blades, combustors, etc.)---all as depicted in the illustration insert. The visual components of the illustration might thus be explained in clear language. This would probably do nicely as an introduction, if anyone is willing to consider such a revision.

As for the rest of article, that's open to discussion as to who might wish to simplify some of the language, if at all, and to possibly provide more visual examples, etc. ?

I don't have the expertise in jet engine technology to do a rewrite, but I am a writer/editor and can offer my editorial perspective if so called upon to do so. (Ronsword (talk) 01:36, 3 September 2008 (UTC))

As a fairly non-technical person, I just came to say that, whilst having to concentrate extremely hard to remember the terminology, I found the level and density of detail in this whole page to be about as perfect. I have some small amount of low level engineering knowledge and can see that any attempt to further abstract many of the concepts being described could break the flow of the description at hand to such a point that comprehension of the overall system might be lost before the reader could rejoin the description of the base system. Interesting to think about the limitations on working memory of the average person, then comparing it to the average person while reading a Wikipedia article, then doing that on a phone screen in a distracting environment compared to a laptop in a quiet environment, then trying to consider which one of those is reasonable to consider a target audience for this sort of content. Maybe breakout boxes might be an idea, maybe a '... for idiots' mode for all of Wikipedia would be a great feature, but I think the length and content of the article is superb, again, in my humble opinion. Thanks to the contributors.

Terminology section

I fail to see the benefit of a terminology section. Most of the terms involved may be wikilinked, and the remaining terms are either self evident, or the current definition does little to help. I'll look at it more closely, but I think I'm just gonna remove it. -Verdatum (talk) 20:58, 14 August 2009 (UTC)

Soviet Work

Arkhip Mikhailovich Lyulka patented a bypass engine (turbofan) in April 1941. Might be worth mentioning, but if so it might be good to compare patents in other countries. DonPMitchell (talk) 03:33, 6 September 2009 (UTC)

Manufacturers Section

I've started taking a look at this article, and the manufacturers section seems like an oddball to me. The list isn't inclusive of all the turbofan engine manufacturers and nothing is cited in it at all. I suggest that everything but the intro paragraph be scrubbed, and that the intro paragraph is properly cited. I'll leave this here for some comment, and if I don't see any opposition, I'll be WP:BOLD and make the edit. Thanks! -SidewinderX (talk) 02:14, 10 June 2010 (UTC)

I agree that there is a conspicuous lack of citations in the Manufacturers section. However, I wouldn't be in favour of immediately scrubbing everything but the introduction. I suggest the {{Unreferenced section}} banner should be added first to give interested Users the opportunity to find suitable citations. This thread on the discussion page also serves to alert interested Users to the problem. If, after a couple of weeks, there are still statements not supported by citations, or there is no sign of anyone working to add citations, that is the time to start culling the original research. Dolphin (t) 02:42, 10 June 2010 (UTC)

Well, I guess the main thrust of my point is that having little blurbs about several of the high profile companies (but not all of them) doesn't serve the article well. I'd be in favor of a paragraph or two listing the largest companies (like the existing intro paragraph does), but I don't think the little blurbs serve the article. If you think it's useful to have something like this, I wouldn't be opposed to spinning it off into a List of turbofan manufacturers article, which could be worked on to become more complete. -SidewinderX (talk) 10:43, 10 June 2010 (UTC)

Ok, it's been nearly two months since I mentioned this... if no one strongly objects, I'm going to cull that section from the article. Thanks! -SidewinderX (talk) 14:23, 4 August 2010 (UTC)

Supersonic: Relative velocity between air and blade

Turboprop and turbofan blades operate in the transonic and supersonic regions in a number of designs because true air speed and rotational velocity (of the blades) add up (vectorially). Such turboprops are too loud for civil operation. Turbofans are more suitable for supersonic operation since they are derived from gas turbine compressors which also tend to work quite good at transonic speeds. Typical design features are thin blades with low curvature and large overlap between blades (look at modern jets like B777, A380). This partially cancels shocks.

Also, can we remove the pure jet-engine stuff please, like high temperature turbine blades?

-- Arnero (talk) 06:07, 19 June 2010 (UTC)

Why? Turbofans have high-temperature turbine blades, too, you know! 86.178.16.44 (talk) 03:49, 16 August 2010 (UTC)

High-bypass

(quote) High-bypass turbofan engines are generally quieter than the earlier low bypass ratio civil engines. This is not so much due to the higher bypass ratio as to the use of a low pressure ratio, single stage fan which significantly reduces specific thrust and, thereby, jet velocity.

This is not correct. High bypass ratio is an essential part of noise reduction. 86.178.16.44 (talk) 03:49, 16 August 2010 (UTC)

Animation of a 2-spool, high-bypass turbofan - Is this animation wrong?

Hi, I had a look at the animation and the arrows for air going through the engine was the same leisurely speed as air bypassing the turbofan. My understanding is that air in the engine is heated and thrust out faster than the surrounding air, generating thrust. The basic principle is that air is compressed in the turbofan, fuel is ignited and the result is spat out the back of the engine to generate thrust compared to the surrounding air (a la Newton's laws).

The animated illustration as I saw it gave no indication of thrust by rapid exit of heated air, as in a jet engine. Am I wrong? Mind you, perhaps my Firefox browser did not display properly, but I still think the air coming out of the engine should be travelling faster than the ambient air-flow... Could someone either correct me or correct the animation? I lack the knowledge or skills to make the changes required, if they are needed.

Please note that this animation is a candidate for 'This is a candidate to be copied to the Wikimedia Commons', so if it is incorrect it should be made correct before any further action. Any explanation as to why I am wrongf or why I am correct would be most welcome! Thanks, Mondegreen de plume (talk) 09:08, 17 November 2010 (UTC)

Hi- I just took a look at the animation, and it looks acceptable to me. If you look, you notice that all the flow arrows hit the front of the engine at the same time, but the flow arrows exit the engine before the outward flow arrows. The only spot that looks a little iffy is that the bypass flow (within the engine) seems to be moving about as fast as the core flow. However, the color of the arrows changes, indicating that it is higher temp (and could also be intereted as increasing the magnitude of the arrows if you want). I don't think that's a deal breaker. Does that help you at all? -SidewinderX (talk) 13:05, 17 November 2010 (UTC)

Hi SidewinderX, I accept your point but to me when just looking at the image i couldn't see any rapid flow, I wasn't tracking individual arrows to see which came out first! I remember that on the TV show 'Top Gear' they showed that the thrust coming from a 747 aircraft is capable of blowing a car off the ground as seen in some movies. My gut feel is that the air coming out as thrust is going a lot faster than the bypass flow - indeed I suspect if you stood in front of one of these engines you could risk being sucked into it! But I'm no expert. If the animation is simply airflow path I guess it is fine, but if it is to show an engine at thrust I think the exhaust flow should be visibly much faster than the bypass flow. If a 747 standing still on the ground can pump out enough exhaust fast enough to blow a car into the air (or even to accelerate from standing still to take-off), that core flow must be a heck of a lot faster than the ambient (still air) around it. Please feel free to correct me as I am not expert here, and if my ignorance and lack of understanding of the animation reveals a way to improve the article or animation caption to prevent others from misunderstanding (I am surely not the only one), then that must make the article better! Mondegreen de plume (talk) 00:02, 22 November 2010 (UTC)

No, don't worry, you're not wrong here at all. I think the animation is still valuable as is -- if I had the technical skills to modify the image to show the core flow moving faster than it is , then I would change it. But I don't have those skills. And you can't really show the flow diagram "at speed" ... jet engine exhaust velocities can be over 1000 ft/s! If you tried to depict that in the animation, you wouldn't be able to see anything! -SidewinderX (talk) 13:41, 24 November 2010 (UTC)

Haha! :-) I guess all one would see if the animation was 'at speed' would be a blur. By the way, many thanks to the person who actually took the time and effort to make the animation to contribute to Wikipedia, great work! (if you would like to know who they are go to the animation page). Like you, SidewinderX, I don't have the ability to modify the animation. However, perhaps the caption could be edited to indicate relative velocities? You seem to have far more knowledge than I, but I suggest maybe a ratio or a range? Something like, 'The animation shows the flow of air through the turbofan but the thrust exhaust (jet, gases, air-stream?) is expelled at a 1000 to 1 rate (or 1000 to 5000 times) as fast as the bypass airflow, this gives the thrust for take-off and flight.' This would give the casual reader (as I was), an indication of the power of the turbofan. Or maybe add as an illustration a picture of a jet at full thrust, I'm thinking here of a pic I saw when reading about the UK's latest aircraft carrier (or an associated article), where there was a pic of a jet with hot blue exhaust coming out. I'm not trying to ask you to do it, but I don't have the technical information, I'm just a passenger from A to B. Tho' I must say I really enjoy the moment of take-off, I always try to get a window seat so I can see the ground go away and then the satisfying rumble and bang of the undercarriage as it gets pulled in says 'I'm flying!' Cheers, Mondegreen de plume (talk) 02:41, 25 November 2010 (UTC)

<quote> the thrust exhaust (jet, gases, air-stream?) is expelled at a 1000 to 1 rate (or 1000 to 5000 times) as fast as the bypass airflow <unquote>

Relax - the cold bypass stream leaves the engine moving almost as quickly as the hot exhaust stream. I don't have any exact numbers to hand but the ratio hot velocity / cold velocity is certainly less than 1.5 109.151.252.179 (talk) 21:31, 14 November 2011 (UTC)

Relative weight of two-spool and three-spool engines

• Under the sub-heading Three spool there is the following sentence:

Because the RB211/Trent designs have a higher IPC pressure rise than the American engines, the HPC pressure rise is less resulting in a shorter, lighter engine.

On 17 April 2011 the word lighter was changed to heavier by IP address 50.92.115.223. It was then reverted by User:Mmeijeri. (See diff.) The word lighter was again changed to heavier by 50.92.115.223 and the following argument was posted in the article. (See diff.) The argument is inappropriate in the article, but most appropriate for the Talk page. I am posting it below to stimulate discussion. I will remove it from the article. I have left an explanatory message at User talk:50.92.115.223. Dolphin (t) 22:41, 17 April 2011 (UTC)

The triple spool design is a heavier engine than the twin spool. Established Data noted below proves this point. After reviewing the data below please change the word to "heavier" in the following sentence below...."Because the RB211/Trent designs have a higher IPC pressure rise than the American engines, the HPC pressure rise is less resulting in a shorter, lighter "should read heavier engine".

Thanks in advance for the correction.

Engine Weight Comparisons for engines with similar thrust.Italic text

http://easa.europa.eu/certification/...700_series_engines-01-06032006.pdf GE: CF6-80E1 Dry Weight: 5,091.62 kg (11,225 lbs). Includes all basic engine accessories and optional equipment as listed in the manufacturer’s engine specs. http://easa.europa.eu/certification/...1-14062004.pdf

RR: T700 series . Dry Weight: 6,160 kg (13,580 lbs). (Not including fluids and Nacelle EBU) http://easa.europa.eu/certification/...1-06032006.pdf

A330-200 O.E.W. weights for each applicable engine http://www.airbus.com/fileadmin/media_gallery/files/tech_data/AC/Airbus_AC_A330_Jan11.pdf GE powered O.E.W. - 119,831 kg RR powered O.E.W. - 119,931 kg

Engines applicable to the A330-300 http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/3c27fd7504a36b648625760e0046cb5a/$FILE/E36NE.pdf

PW 4168 weighs 12,900 lbs.- 5,863 kg

Weight of basic engine includes all essential accessories, but excludes starter, exhaust nozzle, and power source for the ignition system.

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/d69e8a472455be9286257495006282e5/$FILE/E39NE.pdf

RR Trent 772B-60 dry powerplant weighs 14,360 lbs.- 6,527 kg

Engines applicable to the B747-400 http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/a54a5cdbed477da18625753c004dd282/$FILE/E24NE.pdf PW 4062 weighs 9,420 lbs. - 4,273 kg Weight of basic engine includes all essential accessories, but excludes starter, exhaust nozzle, and power source for the ignition system.

http://rgl.faa.gov/Regulatory_and_Guidance_library/rgMakeModel.nsf/0/706579a7e83efab48625727b00751aff/$FILE/E13NE.pdf CF6-80C2B5F weighs 9,790 lbs. - 4,441 kg Weight includes basic engine accessories & optional equipment as listed in the engine manufacturer's specifications, including condition monitoring instrumentation sensors.

http://www.caa.co.uk/docs/1419/SRG_PRO_1048%20iss11.pdf RB211-524H2-T-19weighs 12,573 lbs. - 5,703 kg Dry powerplant weight less intake, intake systems, cowl doors and cowl door support structure.

Engines applicable to the B767-300ER http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/a54a5cdbed477da18625753c004dd282/$FILE/E24NE.pdf PW 4056 weighs 9420 lbs. - 4,273 kg Weight of basic engine includes all essential accessories, but excludes starter, exhaust nozzle, and power source for the ignition system.

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/b015c4c8fa2760a18625765c0053b800/$FILE/E13NE.pdf CF6-80C2B2 weighs 9670 lbs.- 4,395 kg Weight includes basic engine accessories & optional equipment as listed in the manufacturer's engine specifications, including condition monitoring instrumentation sensors.

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/78635932a4cb7e7b862572a70057e006/$FILE/E30NE.pdf RB211-524H-T-36 weighs 12,540 lbs.- 5,700 kg Dry powerplant weight less intake, intake systems, cowl doors, and cowl door support structure.

Engines applicable to the B757-200 / -300 http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/4e1d135907e0ce8686256df1005b1233/$FILE/E17NE.pdf PW 2043 weighs 7,300 lbs. - 3,318 kg

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/1aaba05dd1012e30862574950062f87e/$FILE/E12EU.pdf RB211-535E4-B-37 weighs 7,603 lbs. - 3,456 kg

All the above text was posted in the article on 17 April by IP address 50.92.115.223 - see diff.)

This is OR. The engine is lighter than a 2-spool engine of the same compression ratio and performance, otherwise nobody would ever build a 3-spool engine!!!. Think about it. Rememberway (talk) 21:49, 18 April 2011 (UTC)

• User:Solarsail made the following comments on the Talk page for IP address 50.92.115.223 on 19 April 2011. See diff. Dolphin (t) 00:46, 19 April 2011 (UTC)

Thank you for the explanation, Dolphin 51.

The Type Certificate Data Sheets for the engines noted below is accurate. I fail to understand how one cannot see the logic here with regards to good data. I will post the weights again as some of it line wrapped and made the text disjointed. Thanks again in advance for your review. In general, triple spool engines are heavier than twin spool engines because triple spools utilize a third concentric IPC drive shaft because of an additional HPT rotor disk including two extra bearing boxes with their bearings while a twin spool engine only uses two concentric drive shafts and also two less bearing boxes and associated bearings.

GE engine weight includes basic engine accessories & optional equipment as listed in the engine manufacturer's specifications, including condition monitoring instrumentation sensors. PW engine weight includes all essential accessories, but excludes starter, exhaust nozzle, and power source for the ignition system. RR engine weight excludes intake, intake systems, cowl doors and cowl door support structure.

Engines applicable to the A330-300 GE: CF6-80E1 weighs 11,225 lbs.- 5,091.62 kg PW 4168 weighs 12,900 lbs.- 5,863 kg RR Trent 772B-60 weighs 14,360 lbs.- 6,527 kg

Engines applicable to the B747-400 PW 4062 weighs 9,420 lbs. - 4,273 kg CF6-80C2B5F weighs 9,790 lbs. - 4,441 kg RB211-524H2-T-19 weighs 12,573 lbs. - 5,703 kg

Engines applicable to the B767-300ER PW 4056 weighs 9420 lbs. - 4,273 kg CF6-80C2B2 weighs 9670 lbs.- 4,395 kg RB211-524H-T-36 weighs 12,540 lbs.- 5,700 kg

Engines applicable to the B757-200 / -300 PW 2043 weighs 7,300 lbs. - 3,318 kg RB211-535E4-B-37 weighs 7,603 lbs. - 3,456 kg — Preceding unsigned comment added by Solarsail (talk • contribs) 23:59, 18 April 2011 (UTC)

Thanks Solarsail, your figures look persuasive. It is my understanding that the attraction of a two-spool engine over a single-spool, and a three-spool over a two-spool, is better thrust specific fuel consumption. Improvements in SFC are rarely available at no cost, and in the case of one, two and three spool engines the improved SFC is almost off-set by the increased cost, weight and complexity of the extra spool. I guess Rolls-Royce would argue that the extra cost, weight and complexity of their three-spool engines is more than off-set by the better specific air range of aircraft fitted with their engines. Dolphin (t) 02:00, 19 April 2011 (UTC)

Data presented here shows the three-spool RB211 engine is indeed heavier than two-spool engines eligible for installation on the same aircraft type. There has been no challenge to that data so I have edited the article to change lighter to heavier. That doesn't mean this discussion thread has come to an end - if you have a view on the subject please add it here. Dolphin (t) 02:50, 21 April 2011 (UTC)

Thank you Dolphin from Solarsail.

The "specific air range" of a twin spool engines is superior to a triple spool engines. I can prove it with lots of good data. — Preceding unsigned comment added by Solarsail (talk • contribs) 02:20, 26 April 2011 (UTC)

Dolphin, the following words should be added to the triple spool paragraph. Thanks in advance. "Three spool engines are shorter, heavier, less fuel efficient than twin spool engines and......."

Here is more data to prove fuel consumption.

Fuel Burn Comparisons.Italic text

ICAO Engine Emissions Databank.

http://www.caa.co.uk/default.aspx?catid=702&pagetype=68

A380 with EA or RR engines.

http://www.caa.co.uk/docs/702/9EA001_10122010.pdf EA 7270 - Rated Output - 332.39 kns. Take-off - 2.637 kg/s. Climb-out - 2.169 kg/s. Approach - 0.711 kg/s. Idle - 0.234 kg/s.

http://www.caa.co.uk/docs/702/9RR047_10122010.pdf RR T972-84 - Rated Output - 345.9 kns. Take-off - 2.69 kg/s. Climb-out - 2.230 kg/s. Approach - 0.750 kg/s. Idle - 0.270 kg/s.

A380-800 Payload/Range charts.

http://www.airbus.com/fileadmin/media_gallery/files/tech_data/AC/AC_A380_20101101.pdf GP 7200 engine - maximum structural payload range - 9625 nm. Trent 900 engine - maximum structural payload range - 9525 nm.

B747-400 with GE or Pratt or RR engines.

http://www.caa.co.uk/docs/702/3GE057_01102004.pdf CF6-80C2B5F- Rated Output - 272.53 kns. Take-off - 2.685 kg/s. Climb-out - 2.162 kg/s. Approach - 0.697 kg/s. Idle - 0.206 kg/s.

http://www.caa.co.uk/docs/702/1PW043_01102004.pdf Pratt 4060 - Rated Output - 266.9 kns. Take-off - 2.647 kg/s. Climb-out - 2.085 kg/s. Approach - 0.703 kg/s. Idle - 0.213 kg/s.

http://www.caa.co.uk/docs/702/1RR011_01102004.pdf RB211-524H - Rated Output - 264.4 kns. Take-off - 2.73 kg/s. Climb-out - 2.17 kg/s. Approach - 0.71 kg/s. Idle - 0.26 kg/s.

B777-200ER with GE or Pratt or RR.

http://www.caa.co.uk/docs/702/9GE128_10122010.pdf GE-94B - Rated Output - 431 kns. Take-off - 3.513 kg/s. Climb-out - 2.831kg/s. Approach - 0.876 kg/s. Idle - 0.285 kg/s.

http://www.caa.co.uk/docs/702/10PW099_10122010.pdf Pratt 4090- Rated Output - 408 kns. Take-off - 3.926 kg/s. Climb-out - 2.996 kg/s. Approach - 0.979 kg/s. Idle - 0.338 kg/s.

http://www.caa.co.uk/docs/702/5RR040_01102004.pdf RR T895 - Rated Output - 413 kns. Take-off - 4.03 kg/s. Climb-out - 3.19 kg/s. Approach - 1.05 kg/s. Idle - 0.33 kg/s.

B777-200ER GE/RR range comparisons.

http://www.boeing.com/commercial/startup/pdf/777_perf.pdf The GE90-94B has a fuel consumption of 284.8 lbs/seat for a 3000 nautical mile trip while the RR Trent 895 consumes.......... 291.7 lbs/seat for the same distance.

So the Trent 895 burns 6.9 lbs more of fuel than the GE90-94B for each seat every 3000 nautical miles. With a seat configuration of 300 seats, that equals 2070 lbs or just over a ton more fuel for each 3000nm.

For the 777 with the GE90, the sea level SFC is 0.324 lb/lbth. For the 777 with the Trent 800, the sea level SFC is 0.35 lb/lbth.

GE90 SFC (SLS) 8.30 mg/N-s. (cruise) Trent 882 SFC (SLS) 15.66 mg/N-s. (cruise)

A330-200/300 with GE or Pratt or RR.

http://www.caa.co.uk/docs/702/4GE081_01102004.pdf GE CF6-80E1A4 - Rated Output - 297 kns. Take-off - 2.904 kg/s. Climb-out - 2.337 kg/s. Approach - 0.744kg/s. Idle - 0.227kg/s.

http://www.caa.co.uk/docs/702/9PW092_10122010.pdf Pratt 4164 - Rated Output - 287 kns. Take-off - 2.721 kg/s. Climb-out - 2.239 kg/s. Approach - 0.775 kg/s. Idle - 0.243 kg/s.

http://www.caa.co.uk/docs/702/3RR030_01102004.pdf RR T772 - Rated Output - 316 kns. Take-off - 3.2 kg/s. Climb-out - 2.58 kg/s. Approach - 0.85 kg/s. Idle - 0.28 kg/s.

Airbus Payload / Range graphs.

http://www.airbus.com/fileadmin/media_gallery/files/tech_data/AC/Airbus_AC_A330_Jan11.pdf

A330-200.Italic text Trent 700 - 9,100nm PW4000 - 9,200 nm CF6-80E1 - 9,450nm

( Source for Data required ) A CF6-80 A330 burns 4,700 kg/h and a Trent 700 closer to 5,000 kg/h during cruise.

B767-300ER with with GE or Pratt or RR.

http://www.caa.co.uk/docs/702/8GE101_04102007.pdf CF6-80C2B8F - Rated Output - 267 kns. Take-off - 2.583 kg/s Climb-out - 2.106 kg/s Approach - 0.685 kg/s Idle - 0.205 kg/s

http://www.caa.co.uk/docs/702/1PW043_01102004.pdf Pratt 4060 - Rated Output - 266.9 kns. Take-off - 2.647 kg/s Climb-out - 2.085 kg/s Approach - 0.703 kg/s Idle - 0.213 kg/s

http://www.caa.co.uk/docs/702/4RR037_01102004.pdf RB211-524H-T - Rated Output - 264 kns. Take-off - 2.81 kg/s Climb-out - 2.22 kg/s Approach - 0.77 kg/s Idle - 0.26 kg/s

http://theaviationspecialist.com/350-550_mission_table.gif Note: The GE has a higher cruise thrust than the Trent, but has a lower SFC than the Trent.

GE90-115B - Cruise Thrust - 19,000 lbs. - 84.6 kns. - Cruise SFC. - 0.530 lb/lbth. Trent 970 - Cruise Thrust - 12,700 lbs. - 56.5 kns. - Cruise SFC - 0.561 lb/lbth.

http://theaviationspecialist.com/777-200lr_a340-500s_dmission.gif

GE90-110B1L - Cruise Thrust - 19,000 lbs. - 84.6 kns. - Cruise SFC. - 0.530 lb/lbth. Trent 553 - Cruise Thrust - 10,700 lbs. - 47.6 kns. - Cruise SFC. - 0.568 lb/lbth.

Range Comparisons.

Airbus graphs, with 175t MZFW and 233t TOW:

@ Max structural P/L/MTOW PW4000 - 3,700 n.mls, RR - 3,700 n.mls, GE 90 - 3,750 n.mls. @MTOW/Max tankage PW4000 - 5,500 n.mls, RR - 5,500 n.mls, GE90 - 5,550 n.mls. @ Max tankage/zero P/L PW4000 - 6,500 n.mls, RR - 6,500 n.mls, GE90 - 6,600 n.mls.

This is classic WP:OR. We need a reliable source that states this. Listing any amount of data is irrelevant- we cannot draw conclusions from that without doing WP:synthesis.Rememberway (talk) 02:59, 26 April 2011 (UTC)

Why were the following words removed from the Triple Spool paragraph? T.I.A.

"Because the RB211/Trent designs have a higher IPC pressure rise than the American engines, the HPC pressure rise is less resulting in a shorter, heavier engine". — Preceding unsigned comment added by Solarsail (talk • contribs) 20:09, 27 April 2011 (UTC)

I removed that sentence - see diff. My edit summary states that the material was uncited and therefore possibly original research. Dolphin (t) 22:57, 27 April 2011 (UTC)

According to Rolls-Royce the triple-spool engine is simpler to build and of lower overall cost than a two-spool engine of similar performance — Preceding unsigned comment added by 80.4.57.101 (talk) 14:43, 17 February 2012 (UTC)

Lost the link when I added it - similar 1968 explanation here:[3] "Triple spools permit quieter engine, of lighter, more simple design, and of higher pressure ratio. Competing engines are the twin-spool Pratt & Whitney JT18D and the General Electric CF6/34: the RB.211 is noticeably cheaper than either." — Preceding unsigned comment added by 80.4.57.101 (talk) 22:57, 4 March 2012 (UTC)

Rolls-Royce supply their RB211 and Trent customers with an engine as a complete unit, including RR-designed cowling, etc. ready to fit on the pylon. The other manufacturers only supply the engine, the cowling and other nacelle installations being designed and provided by the aircraft manufacturer themselves: [4] RR have been doing that since the Conway back in the 1950's, but it dates back to the Merlin power-egg, and the later Universal Power Plant (UPP) of the forties used on the Canadair North Star and Avro Tudor.

" ... The "specific air range" of a twin spool engines is superior to a triple spool engines. I can prove it with lots of good data. — Preceding unsigned comment added by Solarsail (talk • contribs) 02:20, 26 April 2011 (UTC)"

"Dolphin, the following words should be added to the triple spool paragraph. Thanks in advance. "Three spool engines are shorter, heavier, less fuel efficient than twin spool engines and......."

"The importance placed on fuel saving by airlines is emphasised by Qantas' adoption of RB211-524 power for its new Boeing 747s - the only aircraft on which all big three fans are available. Qantas found that British Airways' Boeing 747s fitted with RB211s burnt roughly 7 per cent less fuel than its JT9D-equipped fleet, a saving of about $1 million a year at today's prices." - Flight International, 1980: [5]

The RB211 is a three-spool engine, the JT9D a two spool one. — Preceding unsigned comment added by 95.149.172.166 (talk) 15:23, 29 June 2016 (UTC)

References

DB 007

German Daimler-Benz DB 670(designated as the 109-007 by the RLM)

I don't believe this is correct. I believe the 007 was a conventional turbojet with two turbine stages and counter-rotating compressor stages. There was no fan stage, and images suggest the engine was far too small to have one. Maury Markowitz (talk) 15:29, 10 September 2011 (UTC)

There's a new article on the engine with some details here: Daimler-Benz DB 007 — Preceding unsigned comment added by 80.7.147.13 (talk) 10:20, 21 February 2013 (UTC)

strongest turbofan and its power?

sorry for the dumb question (of a non-aeronautic-engineer - for whom wikipedia is also meant, no?): what is for the time being the strongest turbo-fan-engine? how many tons could it lift vertically close to the ground, possibly using also an air-cushion-effect? (and how do you calculate this? N into tons thrust?) sorry again and thanx in advance (also for a lesson in basics)! :-) --HilmarHansWerner (talk) 13:29, 10 February 2013 (UTC)

am I right in saying that a have to divide a thrust-figure in kN by 9.807 kN to get the number of tons the respective engine could neutralize, because in a normal gravitational field 9.807 kN are needed to lift one ton, right? --HilmarHansWerner (talk) 20:37, 12 February 2013 (UTC)

the answer to my question above is probably: GE90-115B: "world record set at 127,900 lbf (568,9 kN) 827 feet above sea level" (http://en.wikipedia.org/wiki/GE90, 11.2.13). correct? however, if I understand the following data well: "Powerplant: 6 × Kuznetsov NK-116 turbofans, 233,000 lb-f (105 t) each" (http://en.wikipedia.org/wiki/Beriev_Be-2500; 11.2.13) then there is an engine twice as strong (because the GE90-115B delivers 115,300 lb-f)...??!! --HilmarHansWerner (talk) 21:02, 12 February 2013 (UTC)

Suck, squeeze etc

This is a well-known phrase. I've seen it used by aeronautical engineering professors in video lectures. Martijn Meijering (talk) 17:51, 25 February 2013 (UTC)

I apologize for the harsh words in my edit summary. I still maintain that it’s a bad way to describe jet engine operation. "Suck" may fit the inlet (although it’s not what it does, just what it "sees") on the taxiway, but come cruise speed air is pushed around the inlet rather than sucked inside it. At supersonic speeds, air is compressed in the inlet and incurs drag. "Bang" and "Blow" are equally ambiguous or misleading.

I think this is just a carry-over from the description of the Otto cycle where it is much more appropriate. Anyway, we can do much better here. Ariadacapo (talk) 18:20, 25 February 2013 (UTC)

When the engine is stationary on the ground the compressor does indeed 'suck' air into the air intake, as anyone who has ever been so foolish to stand too close to one can confirm.

Brayton cycle, temperature and efficiency

An anonymous user removed the statement:

A higher combustion temperature leads to a higher efficiency according to the Brayton cycle.

I agree with this deletion (and so have reverted Teapeat’s edit that reinstated this sentence) for three reasons:

1. It’s not formally true – efficiency increases according to the second principle of thermodynamics, not according to an engine operation cycle
2. A PHD thesis is not a good choice to source such a fundamental, 1850s physics statement (any engineering thermodynamics textbook would do a better job at supporting this
3. Most importantly, it’s not relevant to the article. We could digress into a long discussion of the Brayton cycle (why pressure ratio also increases efficiency, for example) but that is not the role of an introduction to the Turbofan article.

Ariadacapo (talk) 07:34, 4 March 2013 (UTC)

No, it's worse than that. There are two points. One: the removed statement is wrong. Two: the reference does not support it.

Point One - The efficiency of the ideal Brayton cycle depends ONLY on the pressure ratio. See, for example, chapter 12, 'Gas Power Cycles', of Rogers & Mayhew, 'Engineering Thermodynamics Work and Heat Transfer', ISBN 0-582-04566-5.

Point Two - The equation in the reference is shown in R&M as their equation 12.1. If the author of the reference (or his PhD supervisor, or his external examiners) had read down only a couple of lines, during which some minor algebra occurs, he would have arrived at the simple statement, derived from the equation, that 'The efficiency of the ideal cycle is a function of the pressure ratio only'. That is, the equation in the reference doesn't say what the author of the reference claimed that it does, and in particular it does not support the removed statement. 86.183.14.12 (talk) 10:14, 4 March 2013 (UTC)

Well seen... (Just confirmed that with the Rogers&Mayhew, very instructive). Ariadacapo (talk) 19:03, 4 March 2013 (UTC)

References

Thoroughly bad example

In the section 'Low-bypass turbofan': Imagine a retrofit situation where a new low bypass ratio, mixed exhaust, turbofan is replacing an old turbojet, in a particular military application. Say the new engine is to have the same airflow and net thrust (i.e. same specific thrust) as the one it is replacing.

Why 'say' that? - this is not at all realistic. Typically in the real world the new engine does not have the same airflow: consider, for example, the re-engining of the Nimrod with BR700s instead of Speys. (Yes, both are turbofans as it happens, but the principle is the same - the whole point of increasing bypass is to reduce the specific thrust and thereby improve propulsive efficiency). 195.194.10.62 (talk) 14:31, 9 April 2013 (UTC)

Specific examples of what is meant by low/high velocity?

The article talks a lot about low velocity bypass flow and high velocity jet exhaust, but doesn't actually give any numbers. What are some typical flow velocities for a high bypass turbofan, or a low/zero bypass turbojet? 192.171.3.126 (talk) 08:40, 6 August 2013 (UTC)

When you burn fuel and air, it expands (due to heat) and that gives it a velocity. You can get from Carnot efficiency to the (ideal) maximum velocity that exhaust could move. Presumably it is somewhat supersonic, or we wouldn't have supersonic jets. Ideally, and it never is, the exhaust velocity should equal the speed moving through the air, such that no energy is left. Jet airliners go not so much slower than the speed of sound, maybe 90%. So, high velocity might be Mach 3 or so, and low close to Mach 1. One of the difficulties in supersonic jets, is that combustion is subsonic. Incoming air is slowed down (wasting some energy) mixed with fuel and burned, such that the exhaust is now supersonic. Gah4 (talk) 02:44, 18 August 2021 (UTC)

Difference from turbojet in language ordinary folks can understand ?

This is an encyclopedia, not a technojizzforum. So please can we have an explanation that folks without PhDs can understand, of the difference between turbofan and turbojet. Rcbutcher (talk) 07:44, 27 March 2014 (UTC)

I added some lines that try to solve this frustration. "Thus, whereas all the air taken in by a turbojet passes through the turbine (through the combustion chamber), in a turbofan some of that air bypasses the turbine. A tubofan thus can be thought of as a turbojet being used to drive a ducted fan, with both of those contributing to the thrust." A turbofan is conceptually like using a turbojet as the motor to run a fan. Which is not so hugely different, in concept, from a turboprop, except there's a shroud (duct) over the prop/fan. — ¾-10 19:23, 27 March 2014 (UTC)

Works for me. Thanks. Rcbutcher (talk) 04:28, 28 March 2014 (UTC)

One question

Why is specific fuel consumption double at altitude, when compared to take/off? I suppose it is because of pressure ratio? Could we build a more efficient engine, that would be used only for optimal cruise, that would have SFC at altitude equal to T/O?--Pawlin (talk) 15:24, 21 April 2014 (UTC)

Basic Physics Suggestions

The article needs to cover some basic physics as to the pros and cons of the TF. There is too much trivia and 'shop talk' making the article too long.

1. The TF engine is essentially a turboprop but with a shrouded prop. There is a larger x-section of exhaust, but at lower speed. Half of the jet core's power winds up going into powering the fan. The exhaust x-section is made up of the lower-speed fan air, and the higher-speed jet exhaust in the center. The x-flow speed gradient is thus much smaller than for a pure jet. This means much lower small-scale turbulence, and thus a much higher efficiency. Turbulence does not contribute to forward thrust, but it does require power from the engine to be created. The lowered turbulence also lowers the audible engine noise.

2. The TF is less good at increasing speeds. The faster the airplane goes forwards, the faster the exhaust gas needs to go backwards. Via conservation of momentum, the exhaust speed backwards must be much higher than than the a/c speed forwards, as air is much less dense than an a/c. (The 'exhaust' water from ship props has a much lower relative speed, since water is 1000x denser than air.)

3. The fan shroud plays a vital role. It allows the fan to operate at higher revs compared to a simple large-diameter propellor. Props are limited by the tip speed, which must remain subsonic, but the speed of sound decreases at altitude. The shroud compresses the incoming air, increasing the s.s., and the proximity to the fan tip makes the shock wave smaller.

4. Some experiments have been done to remove the shroud and to use small-diameter multiple props turning at high speed (GE36 engine). Composites have allowed propellers to be made lighter and curved backwards (scimitar). The curvature keeps the sonic shock less severe. The curved prop has a smaller diameter and so a lower tip speed, and allows for an increased blade area ratio and hence thrust. Heavy metal props do not tolerate the much increased bending moment at the blade root, caused by the scimitar shape. The bent-lever shape of the scimitar blade means the centrifugal force is transferred to the hub as a bending moment, which is a more difficult engineering problem compared to the simple shear force of conventional straight blades.220.244.87.218 (talk) 02:00, 14 November 2014 (UTC)

The person who makes the suggestions is usually the best one to implement them. eg who else would know what "trivia" and "shop-talk" are, and what source to cite for "compresses the incoming air, increasing the s.s."?Pieter1963 (talk) 23:39, 16 April 2015 (UTC)

current jet engines list

Hello, a table listing current jet engines would be a good thing for comparisons. A good basis would be the jet engines list from Jane's All the World's Aircraft 2005-2006 that I put in a table as I did in Turboprop#Current engines. The List of aircraft engines is too big with many piston engines and defunct engines. Where do you think this list would be more useful? in Turbofan, in Airbreathing jet engine, in a new List of jet engines or List of current jet engines? Or split the List of aircraft engines in propeller/jets, currrent/ancient? thanks for your interest --Marc Lacoste (talk) 15:59, 24 April 2015 (UTC)

removed uncited statement

"engines that use more jet thrust relative to fan thrust are known as low bypass turbofans, conversely those that have considerably more fan thrust than jet thrust are known as high bypass" Perhaps there's an industry standard which covers this "pigeonholing". Why introduce cold/hot thrust ratio? BPR is the standard parameter always quoted with a specific value.Pieter1963 (talk) 23:40, 12 July 2015 (UTC)

Those are common phrases is aviation writing, and not really extraordinary enough to be removed, and certainly not POV. The definition might be a bit odd, but it is basically describing bypass ratio. - BilCat (talk) 00:10, 13 July 2015 (UTC)

A couple of comments.. How do we relate this definition to all those bypass engines with no separate fan and jet thrust? Keep it simple. Use unambiguous bpr (covers all engines and is what everyone else uses) to highlight the relative contributions of the fan and core flow. Fan and jet 'thrust' lose their meaning in the mixer and all the thrust comes from a uniform temperature in the single propelling nozzle (the thrust doesn't "know" where it came from).

Who has decided (not cited, POV?) on this particular categorization for low and high bypass? ie a boundary at bpr 1 and a vague 'considerably more than' boundary for 'high'. What's in between? Trying to come up with categorizations is the life-blood of on-line forums and is best avoided unless they are sourced.

I think the reverted edit is certainly ok for an on-line forum but it falls short for a Wikipedia article. It needs deleting... or modifying. After all, it is "a bit odd".Pieter1963 (talk) 17:13, 14 July 2015 (UTC)

Spools

Why is that there is no redirect for anything related to "two spool" or "twin shaft" on Wikipedia? It doesn't even list "spool" as a component of jet engine on the disambiguation page for "Spool", so one can't even do a search for "Spool (turbofan engine). I have found plenty of pages that refer to "two spool" engines without any kind of explanation, which could benefit from a link. However, about all you can do is link to "turbofan" (and most pages already provide that link), but even then, it doesn't actually explain what "two-spool" MEANS anywhere on this page, that I can see. It say there are single, two, and three-spool designs, but it doesn't give any kind of basic explanation for a layman what the term actually refers too. I'm going to go and see if it says anything on the page on "jet engines" themselves, but since "two-spool" almost always applies to a turbofan, it seems as if a paragraph on this page (and an available redirect to that paragraph) would be appropriate..45Colt 04:54, 11 August 2015 (UTC)

A large bobbin of the sort that might be used in an industrial textile loom.

It is called a 'spool' because the main shaft together with the compressor and turbine disks viewed from the side resembles a bobbin or 'spool' of cotton or yarn, as used in weaving or spinning. See image at right.

Barnoldswick is a former cotton mill town where weaving, spinning and cloth making was the main industrial product.

A two-spool engine will have two separate spools running on concentric shafts, i.e, one running inside the hollow main shaft of the other. A three-spool engine will have one spool running inside the hollow main shaft of the engine, and one inner spool running inside the hollow shaft of the secondary spool.

The first two-spool engine was the Bristol Olympus which was a turbojet, not a turbofan.— Preceding unsigned comment added by 95.149.173.113 (talk) 14:52, 22 April 2017 (UTC)

Last edit

The latest edit with HBPR is a direct copy and paste from several sources on the internet, one of which is NASA (Page 2). Should it be deleted?? -Tanis8472 (talk) 05:48, 19 October 2016 (UTC)

Its point was to inform about chevrons reducing noise. It was already included in the intro but shortly, and with a rotten ref. I'm not sure NASA plagiarism is copyvio as it's a US administration and I believe their work isn't copyrighted, but those additions could be rewrote nevertheless. A balanced view could be useful [6]. --Marc Lacoste (talk) 10:15, 19 October 2016 (UTC)

Lead

The lead is missing basic background information such as the time period during which turbofans have been used, and what aircraft currently use them. For example, if they're currently used on all commercial jets, the article should say so.--76.169.116.244 (talk) 15:40, 15 January 2018 (UTC)

What establishes the initial direction of the flow?

Sorry for this potentially silly-sounding question, but imagine that the turbine is still and is being started. Due to the burning process the pressure would go up. It seems that it would initially press in both directions. Are blades intentionally made asymmetric (the total turbine surface is higher than the total fan surface) so that with the same amount of passing air the angular force that spins in the forward direction is higher? IMO, the article should explain this because this isn't obvious. I'm reluctant to edit the article because I'm not an expert in turbines, and am not entirely sure. Yurivict (talk) 15:59, 1 December 2018 (UTC)

I'm a total amateur on this, but as I understand it, a turbine engine has to be spun up to a speed in which compression and combustion will be effective, thus I assume the starter would determine the spin direction. Hopefully someone else can give you a definitive and more technical answer. As to adding such information to the article, Aircraft engine starting is probably the best place for that kind of information,as this article is about a specific subtype of jet engine. - BilCat (talk) 00:10, 2 December 2018 (UTC)

Yes. Perhaps the starter article should be as clear. Jim.henderson (talk) 00:51, 2 December 2018 (UTC)

There is a story related to the Tu-144 (that might not be in the page) related to restarting engines after flame-out. It seems that the method is to dive to go fast enough, to get enough air moving through, and then fire up the engines. The thought is that doing this, starting too low, is the cause of the crash, though there is no evidence left to show either way. That might also work on non-supersonic engines. Gah4 (talk) 21:06, 8 December 2020 (UTC)

Explanation for reduced efficiency of turbojet

Could you explain why the efficiency is less for turbojets (i.e. the relevant physics/concepts)? "In effect, a turbofan emits a large amount of air more slowly, whereas a turbojet emits a smaller amount of air quickly, which is a far less efficient way to generate the same thrust". Thanks Thelonelyneutrino (talk) 20:09, 1 April 2019 (UTC)

I just saw that it's explained in the efficiency section. I'll add a note to see that section Thelonelyneutrino (talk) 20:12, 1 April 2019 (UTC)

Some would explain it in terms of impedance matching. That small amount of fast air doesn't match the slower speed needed. Turbojets are good if you want to actually go fast. Gah4 (talk) 20:58, 8 December 2020 (UTC)

There is some explanation in Turboprop#Usage as turboprops can vary the propeller pitch for optimal turbine speed. Gah4 (talk) 21:10, 8 December 2020 (UTC)

A Commons file used on this page or its Wikidata item has been nominated for deletion

The following Wikimedia Commons file used on this page or its Wikidata item has been nominated for deletion:

• SaM146 back.jpg

Participate in the deletion discussion at the nomination page. —Community Tech bot (talk) 21:37, 5 September 2020 (UTC)

specific impulse

I wonder if it would be possible to add specific impulse to the table. That is, is it known for enough table entries to make it useful. Gah4 (talk) 23:24, 7 December 2020 (UTC)

Why? If it's the same as TSFC in another unit, it only obfuscates a little bit the tables?--Marc Lacoste (talk) 05:59, 8 December 2020 (UTC)

Other than that TSFC is a disambiguation page so it should be Thrust-specific fuel consumption, then the next question is, can we have that in the table? Otherwise, I suppose I prefer bigger numbers being better, but either one is fine with me. Gah4 (talk) 07:03, 8 December 2020 (UTC)

Well we're talking about Turbofans, obviously TSFC is not a Football club or a Canadian Foundation. For Turbofans, TSFC is the common metric, those are not rocket engines. It would be possible to have a SFC column in the table, but it would be best to avoid a WP:SYNTHESIS of different sources - and TSFC is notoriously difficult to compare, being variable with the conditions. A comparison table including SFC from a WP:RS is already in the TSFC article, so maybe not an urgent need here.--Marc Lacoste (talk) 07:37, 8 December 2020 (UTC)

Maybe not urgent, but it would be nice. Yes I was previously looking at rocket engines where specific impulse seems to be used more. How much of a problem is comparable conditions? One might hope that turbofans are rated at comparable conditions, but I do agree that is a complication. Gah4 (talk) 07:51, 8 December 2020 (UTC)

I would prefer keeping a TSFC comparison in 1 place only to avoid maintenance problems. Other editors input would be welcome. Comparable conditions matter, eg TSFC is often double in cruise than at takeoff, because Propulsive efficiency changes. BSFC (I'll let you pick the more appropriate article if there is a disamb page) is easier to compare.--Marc Lacoste (talk) 08:12, 8 December 2020 (UTC)

Is the civil engines table there only turbofans? If it is, then it should be fine to look there. Can we link to it from here, so people know where to look? If it isn't only turbofans, then I think it is worse than the variable conditions mentioned above. Some of the tables compare rockets and jets, which is fine if that is what someone is interested in, but not for everyone. (And not for those only interested in turbofans.) I don't know them by model number at all, but those who do will have a much easier time crossing between the articles. Gah4 (talk) 14:25, 8 December 2020 (UTC)

Yes. Those interested in TSFC only have to click on the article title.--Marc Lacoste (talk) 18:36, 8 December 2020 (UTC)

OK, I found that one. But since much of the article is on the efficiency of turbofans, it would seem nice to make that easier to understand. The table is pretty far down in the TSFC article, and, as well as I know (I didn't check them) not all turbofans. A column in the table indicating high, low, or no bypass would make comparison easier, or an indication that all are high bypass turbofans. Gah4 (talk) 18:56, 8 December 2020 (UTC)

I'm not sure which article you're talking about, can you be more specific? thanks.--Marc Lacoste (talk) 20:15, 8 December 2020 (UTC)

This article is on turbofans and has a table comparing many different models. The table does not include any column related to fuel consumption or efficiency. Thrust-specific fuel consumption has a table that may include other than turbofans, since the article is more general. One possibility which I know is done, but I haven't done, is to put the table in a template and transclude in more than one article. Possibly even with parameters so that it is different, selecting rows or columns to include. Otherwise, it is difficult to compare engines on the table in this article to ones in Thrust-specific fuel consumption, unless one has memorized the names. (I suspect that people who work on them all day have, but most of us haven't.) While it isn't so much in the news now, there was some about how much more efficient the 737MAX is than other models. That means less fuel costs, and less carbon emissions, good for airlines and all of us, respectively. Gah4 (talk) 20:50, 8 December 2020 (UTC)

Why not, but the TSFC column would still be more relevant in the TSFC article than in the Turbofan article. Yes, most interested people know the few turbofan families. It would be difficult to have comparable TSFC figures for recent engines as we have to get a comparison from a RS first. But if you only want to know the improvement of the CFM LEAP over its predecessors (15%), it's in the CFM LEAP article.--Marc Lacoste (talk) 05:51, 9 December 2020 (UTC)

deleted tagged statement

The statement doesn't recognize the trade-off studies that are required in choosing the engine cycle. It's a bit like saying 3 engines are best for business jets......because the Dassault 7x needs 3. More specifically for the particular deleted statement, which probably had the Concorde in mind as to why a turbojet is best at M2, here's a dated example which shows the experts don't choose without trade-off studies: "Rolls-Royce/Snecma are studying fan, leaky turbojet and duct burning Olympus derivatives" for M2. Their studies showed lowest cruise sfc with bpr > 0.6. Ref Flight International 11 May 1972.Pieter1963 (talk) 23:03, 16 February 2021 (UTC)

the Tu-124 turbofan airliner

The article says the first turbofan series-built airliner was the TU-124 in 1962. As the Conway Boeing 707-420 entered service in 1960 does this mean the 707 was not series-built? ie what does series-built mean? Thanks.Pieter1963 (talk) 02:02, 17 February 2021 (UTC)

Refs are shaky : GlobalSecurity.org and aerospaceweb.org are subpar. It may not even be the 707 : Rolls-Royce Conway turbofans powered a 707-420 into the air on May 20, 1959, but it was a Douglas DC-8-40 using similar engines that entered airline service first on April 1, 1960[7]. --Marc Lacoste (talk) 07:55, 17 February 2021 (UTC)

For GE Aviation, the energy density of jet fuel still maximises the Breguet range equation

Does anyone know, is GE special in this regard or is it just a general statement which applies to the Breguet range equation for any aircraft? Thanks.Pieter1963 (talk) 18:57, 17 February 2021 (UTC)

It's a general statement, representing the POV af GE as reported by aviation week.--Marc Lacoste (talk) 20:42, 17 February 2021 (UTC)