Talk:Jet engine/Archive 2

Archive 1

Archive 2

Archive 3

Archive 4

Jet Engine Performance

This here is an obscenely huge article, and far too related to Jet Engine that the two should coexist without cooperation. Any thoughts on the matter? Jet Engine is already a bit too long, and begs a few sub-articles be created, and J.E.P. sees the same problem. Scaller (talk) 10:22, 10 April 2008 (UTC)

Image:Jet engine.svg

Just wondering, why was this Featured Picture removed in favor of Image:Turbofan operation.png? Note that I know little about jet engines, but in general Featured Pictures should be preferred over non-featured ones. If there's a problem with Image:Jet engine.svg, that's fine, but I just wanted to know. howcheng {chat} 04:46, 22 April 2008 (UTC)

The whole point of the picture is so the article can talk about the various features it has. We need a turbofan diagram in the article, because it has features that turbojets simply don't have. Essentially all current jet engines are turbofans. Even the turbofan picture currently in the article lacks an afterburner section and the bypass duct is a bit sketchy, but it's still a better picture for the article. We really need an even better picture still.- (User) WolfKeeper (Talk) 05:19, 22 April 2008 (UTC)

Thanks for the explanation! howcheng {chat} 16:04, 22 April 2008 (UTC)

Just tell me what you want me to draw, is figure 15-2 from this FAA handbook what you are looking for? Jeff Dahl (Talk • contribs) 23:50, 22 April 2008 (UTC)

it's a very nice picture indeed, but it really needs an afterburner; a low bypass military turbofan with afterburner. Something like: Low-bypass-turbofan-with-afterburner only not copyright, and not as awful ;-)- (User) WolfKeeper (Talk) 02:39, 23 April 2008 (UTC)

I can't seem to access the link, it must require a Britannica subscription. Any other source materials? Jeff Dahl (Talk • contribs) 03:00, 23 April 2008 (UTC)

That's odd; I don't have an account. Try googling for the image with "Low-bypass turbofan with afterburner" it was the first thumbnail when I did it.- (User) WolfKeeper (Talk) 03:24, 23 April 2008 (UTC)

I'm getting the phrase "There was an error while trying to display this page" whether I click on the link or google it. Jeff Dahl (Talk • contribs) 03:26, 23 April 2008 (UTC)

You seem to have a network problem. You could try pointing your browser to a proxy server, that normally circumvents these kinds of issues.- (User) WolfKeeper (Talk) 00:20, 25 April 2008 (UTC)

If there's something wrong with the featured image, I would like to see it improved and rectified rather than replaced, because I think it's a much better jumping off point than the png.--HereToHelp ^{(talk to me)} 23:18, 24 April 2008 (UTC)

Let's just say that I would prefer to not see editorial decisions being made solely on the basis of file formats.- (User) WolfKeeper (Talk) 00:20, 25 April 2008 (UTC)

Try this URL for the Britannica image. Kaldari (talk) 20:23, 1 May 2008 (UTC)

Shortening, merging and new articles

Hi, my edit of the 10th of April (two up) didn't get much attention, so I thought I'd try again. =) The article needs to be shortened, especially so it may reach the quality it deserves for being such an important topic, and being featured. I envision the article should cover the jet engine much like it currently does, and should not lose more than half its length. Right now, Major components seems to be taking up a lot of space, and could be shortened down. A lot of the other sections, heartily elaborated on, could also lose the fattening bits. I understand that the jet engine is a very complex machine, and thus an article is far-reaching. If there isn't any actual desire to shorten the article down, there should be an established consensus on this in the form of a vote or similar.

To have an article of great size, such as it is now, is not particularly in keeping with how other far-reaching articles (in science, say quantum dynamics and so forth) choose to fork out and distribute their topics. See Nuclear reactor, for instance, which leads to Nuclear power (keep in mind much of the length is references) and all its other subjects. A similar overhaul for Jet Engine could provide equally good results, if this is desired. To make myself clear, I don't see the article greatly troubled by its length, but its focus spans quite a lot of the intrinsic parts of the engine, perhaps too much.

Jet Engine Performance was also mentioned by me on the 10th of April. This has so far not received much in the ways of editorial love, which it dearly needs. A discussion about this topic is best had over at JEP itself, but if Jet Engine is more of an umbrella article, spanning all components of the engine, JEP sees the potential to be broken down into bits that are then merged with the articles created for, say, parts of Jet Engine and its daughter articles. JEP should exist on its own. Among the things to do on the actual article is serious reference-work, making .svgs for the charts, overall formatting, you name it.

These are only proposals, and I am entirely dependent on the assistance, not to mention the superior factual knowledge on the natures of these topics, that the contributors of Jet Engine possess. Scaller (talk) 21:22, 6 May 2008 (UTC)

Oil prices

Are facts about 2007's high oil prices truly relevant enough to be mentioned in the first paragraph of this article? 68.110.203.201 (talk) 19:49, 30 September 2008 (UTC)

I agree. It's irrelevant and ought to be removed. I tried to remove it, but my edit was reverted by the same user, twice. Unfortunately, some people here think a Wikipedia article should have everything including the kitchen sink, regardless of relevance, article flow, or just plain common sense. It totally baffles me. Shreditor (talk) 04:25, 1 October 2008 (UTC)

While I'm not necessarily that bothered about the oil prices themselves, you also removed the bit about jet engines burning a large fraction of the planets oil every year. The introduction is supposed to be putting things into context...- (User) Wolfkeeper (Talk) 05:07, 1 October 2008 (UTC)

Again, how is it relevant to THIS ARTICLE? I don't see how political, economic, or social problems are relevant to a discussion of technology. Besides, the exact same statements with the same references are already in the jet fuel article, where they make a lot more sense. These technical articles are already hard enough to read for the layperson. Keep it simple, folks. Shreditor (talk) 00:26, 2 October 2008 (UTC)

The article isn't about the technology of jet engines, it's about jet engines and everything important about them. That's what encyclopedias do.- (User) Wolfkeeper (Talk) 01:28, 2 October 2008 (UTC)

I disagree. It's a technical discussion. In fact, it's above technical. It gets a lot in to engine theory, and is purposely light on specifics and statistics. So having this idiotic political conjecture in the article, especially right in the intro, is inappropriate. Shreditor (talk) 23:32, 2 October 2008 (UTC)

Ummmm. So your argument is that its already too heavy on technical, so it's important to remove all the other stuff. As in: huh?- (User) Wolfkeeper (Talk) 01:37, 3 October 2008 (UTC)

No, my argument is that the article is technical by its very nature, and having trivia in the article which distracts the reader from the technical material is inappropriate. I'm not sure how I can make it more clear than that. Shreditor (talk) 06:33, 3 October 2008 (UTC)

Albert Fonó

It sounds like Albert Fonó's 1928 patent is on ramjets- these work best at about Mach 3, but are really difficult to get started. Does anyone know of a really good reference on this guy- I did a web search, but nothing very solid turned up. I think that the claim that he 'invented the jet engine' is totally stretching it, the aeolipile was invented much, much earlier, and there's prior art on ramjets from Leduc. If his patent actually covered turbojets then that might be a different thing, but I'm not comfortable with any of the fluffy references I've found to allow that in the article right now.- (User) WolfKeeper (Talk) 20:19, 10 June 2008 (UTC)

^ *Gyorgy, Nagy Istvan, “Albert Fono: A Pioneer of Jet Propulsion”, International Astronautical Congress, 1977, IAF/IAA ^ Dugger, Gordon L. (1969). Ramjets. American Institute of Aeronautics and Astronautics, p. 15. —Preceding unsigned comment added by 89.223.193.226 (talk) 20:00, 9 August 2008 (UTC)

I have been unable to confirm this, and a linked pdf loaded with glacial slowness, and then died leaving no mention of fono in the broken remnants. Anyone?- (User) Wolfkeeper (Talk) 03:03, 30 December 2008 (UTC)

So far as I can tell this seems to be undue weight, but if somebody has the patents we might be able to tell.- (User) Wolfkeeper (Talk) 03:04, 30 December 2008 (UTC)

My dear friend, Wolfy! about aviation, the IAA organization (American Institute of Aeronautics and Astronautics) is similar to Nobel commission in scietific world. It is considered as THE "official" opinion about aviation science. The pdf is only 4Mbyte. As I realized, you are not a computer genious :))) download the pdf. Belive me, every pdf readers have searchers. Type the pdf searcher: Fono , or type the patent numer. —Preceding unsigned comment added by 77.111.185.112 (talk) 08:56, 30 December 2008 (UTC)

OK, I've loaded it now (it appears you have to save it and then open it rather than load it in a browser- it appears to be a bug in adobe's reader). The relevant text reads:

102 ALBERT FONO: A PIONEER OF JET PROPULSION Nagy Istvan Gyorgy 1977 - IAF/IAA 77-A-14 - vol 4 - AAS vol. 9 - pp. 277-281 The outstanding Hungarian engineer Albert Fono was one of the pioneers of jet propulsion. His first invention of this kind the "sertial torpedo" dates back to the World War I, to the year 1915. He wanted to get a solution for increasing the range opf filed-artillery guns. According to the inventor's conception the gun-launched projectile could be united wit a ramjet propulsion unit by which the body gained acceleration. By this means it was possible to attain a long range even at low initial velocities, and heavy shells could be fired from guns of small weight. Fono submitted his invention to the Austro-Hungarian Army H.Q. but the proposal was rejected. Long after the war Fono took up the problem of jet propulsion again. He elaborated in 1928 the "air-jet engine" which was suitable for high-altitude supersonic aircraft and applied for a German patent. In an additional patent application the propulsion unit was adapted for subsonic speeds too. The patent were granted in 1932 with the priority date of May 1928 as these are the earliest which cover all the essentials of present aircraft and missile air-breathing jet engines.

But that aside, you seem to be repeatedly inserting incorrect spellings and deliberately messing up the formatting of the article in a self-serving manner. You're also adding material in non time order, which again seems to be deliberately aggrandising. These are usually signs that something non NPOV is going down. It seems to be pretty clear to me at least that nobody really invented the jet engine, maybe of all Griffith has the best claim to it, he was the one that worked out how to make compressors work; without his work on axial compressors, none of it would work for aircraft; and everything else seems to have been comparatively straightforward.- (User) Wolfkeeper (Talk) 14:25, 30 December 2008 (UTC)

Article size reduction

The article is currently running at 98K, which is much too big.

I measured the components section at about 40k, so I think there's a strong argument that we should split that off into its own article and use summary style from here. That may get the size down to about 60K, which would be a bit more manageable and a lot more readable.- (User) Wolfkeeper (Talk) 15:45, 17 January 2009 (UTC)

Any comments before I do this? Any other suggestions for space saving?- (User) Wolfkeeper (Talk) 15:45, 17 January 2009 (UTC)

An image listing all the various sorts of jet engine

File:Jet engine types.png

I'm sure this will be helpful. Andy Dingley (talk) 23:06, 13 July 2010 (UTC)

Turboprop/shaft

It's a good question to raise whether or not they should be included in the list of airbreathing jet engines. I think they should be kept in the list (maybe with a caveat bluntly stating that they are not jet engines by the definition that the article uses). While they aren't technically jet engines (rather they are gas turbines), they are commonly discussed in the same breath as other gas turbine engines. I think it is useful for the reader to have a brief comment and link to the main article. Furthermore, they are discussed in the "comparisons" section later in the article. -SidewinderX (talk) 17:17, 30 June 2010 (UTC)

I'd support their inclusion, to a paragraph and hatnote at least, for a number of reasons:

• Their inclusion is expected. We shouldn't disappoint, or even worse confuse, readers.
• Their development and internal operation is inextricably linked to "pure jets".
• They are after all jet engines. Exhaust jet efflux is a significant source of thrust.

I would on this basis revert the recent deletion. Andy Dingley (talk) 18:07, 30 June 2010 (UTC)

That last edit removed the Propfan entry as well, which I disagree with. As Andy points out, turboprops and propfans produce a non-negligible amount of thrust from the exhuast jet (the FAA says ~10%) (NASA, FAA Handbook). Most importantly, in my mind, is the fact that a reader will expect to see something there. I didn't revert the last edit because I don't want to start an edit war (particularly because we're both trying to improve the article!), and I'd like to hear your reasoning before we decide what do to. -SidewinderX (talk) 18:26, 30 June 2010 (UTC)

They do not seem to me to be jet engines, in the sense that the majority of their thrust does not come from jet propulsion. Even a car, or more or less any aeroengine has some propulsion from its exhaust gases. Do you have a reference that they are correctly considered to be jet engines?- Wolfkeeper 19:16, 30 June 2010 (UTC)

That's not the main point I'm trying to make, but for the sake of discussion, do you have a source that states that a jet engine is defined as something that produces 50%+ of its thrust by jet propulsion?

I think the more important point is that a reader will expect to find turboprops and propfans in a list of jet engines. I think that adding a comment about how little of their thrust is due to jet thrust would be the right thing to do, but I still think they should be included. Every book I have ever seen about jet engines or propulsion has described turboprops in the same group with turbojets and turbofans. Including several sentences about them with links to their proper pages does a lot of good in my mind. -SidewinderX (talk) 19:33, 30 June 2010 (UTC)

I agree a brief mention of these intermediate forms combined with an appropriate wikilink would be a good idea. Martijn Meijering (talk) 19:36, 30 June 2010 (UTC)

I don't have a problem with them being mentioned somewhere, but they should not be mentioned in such a way as to imply that they're jet engines, unless we have a reference for that.- Wolfkeeper 20:55, 30 June 2010 (UTC)

What is your definition of a "jet engine" then? Because if "they're really not", then that can only be said with confidence if there's an accepted definition of what a jet engine is, and by implication what they're not. It's difficult to define disjoint sets like this: the more precise the definition, the less readable and less useful it tends to become. We're not even here to define taxonomies: our role is to explain and to communicate. That's usually achieved more usefully by imparting a clear understanding of an imprecise group, not by getting tied in knots over just exactly what is and isn't. Andy Dingley (talk) 21:04, 30 June 2010 (UTC)

We're here to summarise reliable sources aren't we?.- Wolfkeeper 21:22, 30 June 2010 (UTC)

"Significant" doesn't have to be a majority. Andy Dingley (talk) 20:05, 30 June 2010 (UTC)

Do we have a reference that they're considered jet engines or not?- Wolfkeeper 20:55, 30 June 2010 (UTC)

There's a rack of books here on aircraft jet engines. All (inc. the ubiquitous R-R handbook The Jet Engine, which covers turboshafts too) except two could be said to describe turboprop engines listed in along with other jet engines. The two that don't are because one of them pre-dates the turboprop (Geoffrey Smith, 1945, Gas Turbines and Jet Propulsion for Aircraft, which does however include the Caproni-Campini CC2) and the other P&W handbook only refers to both as "the aircraft gas turbine engine" and doesn't seem to like the term "jet" at all. A common approach (Gunston & others) is to cover both, but title the overall work as "Jet and Gas Turbine engines").

Jet engine is a lightweight top-level article with a broad scope, and it's that rare beast on WP, a broad article that might actually get a decent structure. It should be generous in the scope of its coverage, restrictive in its depth. Some readers should find their questions answered, most will be directed through to an in-depth article, none should find their search target missing. Andy Dingley (talk) 21:19, 30 June 2010 (UTC)

It seems to me you're saying that these books don't define them as jet engines, but as gas turbine engines.- Wolfkeeper 21:28, 30 June 2010 (UTC)

Perhaps so, but what they don't do is to isolate turboprops away from turbojets. Andy Dingley (talk) 21:35, 30 June 2010 (UTC)

"Jet and Gas Turbine engines"- they're doing a how-to on gas-turbine aero-engines. I'm not at all opposed to an article on that topic, but that's not this article. I think an article on jet engines, has to cover jet engines, and at most mention/compare/contrast other types of engines.- Wolfkeeper 00:09, 1 July 2010 (UTC)

I'm afraid I still don't see what the problem is here. We're not talking about a 500 word essay on turboprops to be added to the article, we're talking about a couple of sentences describing what they are, how they're similar to other jet engines, and, as you have correctly pointed out, how they are different. This seems like a no-brainer to me; we're going to make the article more useful for the reader. Period.

If you're still concerned about "how much" of a jet engine a turboprop is, NASA includes a jet thrust component in their very basic jet engine description. To add another example to Andy's lengthy list, Flack describes turboprops in his Fundamentals of Jet Propulsion with Applications. He also states "The thrust from this engine type is developed from two sources: the propeller and the turbojet nozzle". That same book also discusses propfans. Again reiterating what Andy said, the literature does NOT isolate turboprops from turbojets and turbofans, and neither should Wikipedia. -SidewinderX (talk) 02:27, 1 July 2010 (UTC)

To digress further, what about turboshafts? There's a reasonable case for notincluding these under jet engines, just as there is for including the turboprops. Andy Dingley (talk) 15:20, 1 July 2010 (UTC)

Both of them are very typically optimised to minimise jet thrust; any propulsion from jet thrust represents a loss of energy. The optimum use of the pressure from the compressor is to use it to develop energy for the shaft. I don't therefore consider them to be combined cycle jet engines, they're just gas turbines.- Wolfkeeper 17:13, 1 July 2010 (UTC)

Your uncited claim might hold some water for turboshafts developed after turbojets (remember that pure shaft-drive gas turbines developed as such and in commercial service pre-date Whittle et al by a decade) but claiming that turboprops are optimised to minimise jet thrust has nothing to back it up, and no evidence from data for typical engines. In particular, look at the very first turboprop engines (perhaps the Trent) when they were literally just the current model of jet engine, with an extra turbine stage to drive a propeller gearbox. Although this turbine obviously extracted power from the exhaust and reduced its thrust, this is far from "optimising" its reduction or "minimising" it. Secondly, with a typical jet thrust proportion of 10%, that's not a negligible amount and it certainly isn't a "loss of energy", which is why turboprop jetpipe design is taken as seriously as exhaust ejector or cooling system outlet design was for piston fighters in 1945. Andy Dingley (talk) 19:09, 1 July 2010 (UTC)

The point is still that it's not a jet engine, and unless you have a reference that it is, the article cannot imply that. The correct place to be making points about the similarities between the different types of aircraft engine is at aircraft engine.- Wolfkeeper 01:09, 2 July 2010 (UTC)

As above, R-R The Jet Engine A whole book about jet engines, under that title, and right in there amongst them are turboprop engines. It's also worth noting that that they don't use the term "jet engine" to mean anything other than the inclusive set. Otherwise they're quite specific as calling turbojets "turbojets" and turbofans "turbofans". Andy Dingley (talk) 22:20, 2 July 2010 (UTC)

break

Ok, let's step back from the argument about the percentage of thrust derived from from the jet and whatnot. To me, this is the key argument-- Wolf is arguing that because turboprops and propfans are not pure jet engines, but rather gas turbines, they shouldn't be included in the article. Andy and I are arguing that they are so often grouped together in the literature that a reader would expect to see them mentioned here.

Wolf, I'm still struggling to see why you are so opposed to mentioning them here. I've made it clear that it makes sense to include a hefty caveat that they aren't strictly jet engines. How does mentioning them for the sake of a non-expert reader hurt this article?

This is the content that I think should be added back to the article (tweaked to make the differences more clear). What do you oppose so much about this section? -SidewinderX (talk) 21:06, 1 July 2010 (UTC)

---

Turboprop and turboshaft

Main article: Turboprop

Main article: Turboshaft

A turboprop engine is a gas turbine engine that uses its gas generator (compressor, combustor, and turbine) to spin a propeller to generate most of its thrust rather than high speed exhaust. Despite that fact, turboprops are often considered with traditional jet engines in literature because they share they share many other characteristics. Turboprops generally have better performance than turbojets or turbofans at low speeds where the propeller efficiency is high. Turbofans become more efficient than turboprops at higher speeds. Turboshaft engines are very similar to turboprops, differing in that the power produced by the engine is supplied to a shaft rather than a propeller. They therefore generate no jet thrust. Turboshaft engines are often used to power helicoptors.

Propfan

Main article: Propfan

A propfan engine (also called "Unducted fan", "Open rotor", or "Ultra-high bypass") is a gas turbine engine engine that uses its gas generator to power an exposed fan, similar to turboprop engines. Like turboprop engines, propfans generatre most of their thrust from the propeller and not the exhaust jet. The main difference between turboprops and propfans is that the propeller blades on a propfan are highly swept to allow them to operate at much higher speeds, about Mach 0.8, which is competitive with modern commercial turbofans. These engines have the fuel efficiency advantages of turboprops with the performance capability of commercial turbofans. While research and testing (including flight testing) has been done on propfans, no propfan engines have entered production.

---

The primary problem is whether they are, or are not considered to be jet engines. It doesn't matter whether you or I think that they are or are not. The only thing that matters in the Wikipedia is whether you have, or can get references to that. Right now, you do not have references, so they should not be included in this article, which is about jet engines.- Wolfkeeper 22:44, 1 July 2010 (UTC)

So readability and article structure isn't even on your radar ? Andy Dingley (talk) 22:51, 1 July 2010 (UTC)

Wolf, right now the article does not have a cited definition of jet engine, so I find it hard to seriously consider your position here. It doesn't matter to you that nearly every piece of literature considers turboprops in the same pages at they consider turbojets? Just that, in your mind, they're completely different things and shouldn't even be addressed in the article?

• Propfan - One of several terms used to describe new generations of jet engines which typically turn very large, multi-bladed propeller-like fans in order to produce the thrust needed for flight. [1]
• Turboprop - a jet engine designed to produce thrust principally by means of a propeller driven by a turbine with additional thrust usually obtained by the rearward discharge of hot exhaust gases [2]

Can we finally put this to bed? -SidewinderX (talk) 22:15, 2 July 2010 (UTC)

Let's evaluate the sources. The first isn't a reliable source, it's not a printed book, it's not a journal entry. The second is a dictionary, I don't personally consider them to be reliable sources for encyclopedic topics either, dictionaries capture common usages, not accurate meanings, but feelings may vary on that. I think that at best it's saying that a turboprop is a combined cycle propeller/jet engine.- Wolfkeeper 13:01, 3 July 2010 (UTC)

Wolf, again, the article doesn't have a cited definition for "jet engine" in it, so your attitude towards turboprops and propfans are astounding to me. Furthermore, I don't understand how you can argue against the dictionary definition of a turboprop --- you're position is that it captures common uses! Are you saying that there is no value in wikipedia covering the common usage of a term? -SidewinderX (talk) 16:18, 3 July 2010 (UTC)

To my mind there seems to be some mention of the turboprop (and shaft) in the text. At the moment, it looks like it's been purged - The section of history gives the impression that there was no alternative to piston engines in airliners until the 1970s.GraemeLeggett (talk) 13:59, 6 July 2010 (UTC)

FWIW I checked the Encyclopedia Britannica. They seem to define Jet Engine[3] more or less as we do (although they restrict their article to internal combustion aircraft engines). They also define turboprop as a 'hybrid engine'.[4]- Wolfkeeper 18:11, 6 July 2010 (UTC)

Well, the next words in that sentence about the turboprop are "that provides jet thrust". I guess I'm still struggling to see what you dispute in the text I proposed above. Besides the points Andy and I have tried to make, I think that these other sources (no matter how reliable you consider one of the most popular dictionaries to be) show that turboprops are, at the absolute least, commonly associated with jet engines. If you dispute something that the text factually states, let me know and we can looks for sources to change or reinforce it. But I just can't see how a few factual sentences about something that people expect to read is innaproppriate for the article. -SidewinderX (talk) 19:39, 6 July 2010 (UTC)

They've clearly not jet engines, since a jet engine is propelled essentially only by jet propulsion. They're hybrid engines (at best) because they get some jet propulsion.- Wolfkeeper 19:53, 6 July 2010 (UTC)

The fact that they're associated with jet engines, well plenty of things associate, that doesn't mean that they should necessarily be covered in the same article. Sure, you can mention them as associating. I mean Tony Blair associated with G.W.Bush, but that doesn't mean you should cover them in one article. But you're allowed to explain the association.- Wolfkeeper 19:53, 6 July 2010 (UTC)

I guess I just don't understand why you want to define this article so narrowly. This article, by nature, is of the "mile wide, inch deep" type. Almost every section does, or will have, a link to a "main article" that goes into the real detail of the topic (be it Turbofans or History of the jet engine). Turboprops will be discussed, at least, in the history section and the "comparison" section. Why not include otherwise include them? The basic physics princples espoused by this article also apply to turboprops. I still disagree with your characterization that "jet engines (are) propelled essentially only by jet propulsion". -SidewinderX (talk) 12:05, 7 July 2010 (UTC)

Let's drop the term "jet engine" entirely. Turbofans are not turbojets, no more than they are turboprops. What we do find is that the industry loves to talk about jet cores http://www.rolls-royce.com/defence/products/helicopters/ae_1107C_liberty.jsp "Shares a common core with AE 3007 and AE 2100 family of engines" so how about switching our term of use to "jet powerplant" for anything that isn't just a turbojet? Hcobb (talk) 15:08, 6 July 2010 (UTC)

Well, as Wolf has pointed out, this article is about jet engines in general, not specifically aircraft powerplants. (Hence the inclusion of water jets in the article). The debate is about whether or not turboprops and propfans should be mentioned in the article in the manner described above. -SidewinderX (talk) 16:41, 6 July 2010 (UTC)

I suggest either a mention in the Gas turbine paragraph or put the links in a {{seealso}} template, e.g.

See also: Turboprop, Turboshaft, and Propfan

since they are related technology. -Fnlayson (talk) 01:07, 8 July 2010 (UTC)

I was suggesting that they go as a level 5 (I think) heading under the level 4 heading of "Turbine Powered". Am I correct in interpreting your comment as in you do not think they should have an explanatory paragraphy like Turbojet has, just a see-also link? -SidewinderX (talk) 11:27, 8 July 2010 (UTC)

• Right, not a another subsection. Just a couple sentences at the end of the turbine paragraph Or the see also link. -Fnlayson (talk) 12:23, 8 July 2010 (UTC)

A few notes on what I've seen of this discussion (and I limit my discussion to aircraft jet engines):

• Relying on a strict definition of what a jet engine 'is' is problematic, as evidenced by this discussion. If we're arguing that a jet engine require the formation of a jet of air to produce thrust, well, quite honestly, propeller-driven aircraft produce a "jet" of air, but they are certainly not jet engines. If we say it requires a Brayton cycle (thus eliminating most propeller-driven engines), then ramjets are not jet engines. If we rely on a hot-jet exhaust for optimal thrust production, then turboprops are most certainly jet engines (see below). If we require a jet engine to obtain its thrust from a ducted jet, then turboprops/turboshafts/propfans are excluded; however, I have never come across a source that defines a jet engine as requiring a duct.
• Turboprop/turboshaft/propfan engines are NOT strictly gas turbine engines: all three rely, more or less, on an optimum balance of power extracted by the turbine to hot-jet exhaust velocity [Hill, Philip, Carl Peterson, Mechanics and Thermodynamics of Propulsion, Second Edition. New York: Addison-Wesley. 1992. Page 190]. Thus, a portion of maximum thrust is strictly due to a hot gas jet: as was noted earlier, around %10 in some cases. So, if we require a jet engine to obtain thrust from a "jet" of fluid from a nozzle, they should be included.
• According to The Airplane Flying Handbook, a turbofan engine can attribute 30-70% of its thrust to the fan, and high-bypass turbofan engines prevalent on modern commercial aircraft are without a doubt pushing the upper bounds of that. If we require the majority of thrust to be obtained from the hot-jet, then turbofans cannot be included.
• Turboshafts and turboprops are mentioned, in my experience, alongside turbojet and turboshaft engines, all under the heading of "jet propulsion" engines. Moreover, I have often heard of turboprops described as "un-ducted" turbofans, or vice-versa. In Hill & Peterson (cited above), "Turboprop and Turboshaft Engines" is a stand-alone section of a chapter entitled "Thermodynamics of Aircraft Jet Engines", immediately following the section "Turbofan Engines". A significant portion of this chapter is devoted to cycle performance of un-ducted fan propulsion typified by turboprop and propfan engines. Here we have a credible source including turboprop/propfan and turboshaft engines under the heading of "Aircraft Jet Engines," which is exactly what this argument is about.

Now my own personal opinion: Turboprops/propfans and turboshaft engines should be given a due amount of space in this article under the section "Turbine powered," just as turbojet and turbofan have been given: not a large amount of space, but enough to identify these types of propulsion, differentiate them between turbojets and turbofans, and links to main articles. In brief:

• The only significant (and very generalized) difference between turboprop/propfan engines and turbofans are that they lack a fan duct.
• They are NOT strictly gas-turbine engines, as a portion of their thrust is, by design, due to the hot-jet exhaust.
• At least one credible (and I would even say authoritative) text includes turboprops and turboshaft engines as types of jet engines.
• I suggest turboprops/propfans and turboshaft engines be included while noting their differences to turbojet and turbofan engines. ---GreyTrafalgar (talk) 16:14, 13 July 2010 (UTC)

So far as I am aware ramjets do use the Brayton cycle, they just use ram effect for the compression, rather than a rotary-style compression system.- Wolfkeeper 22:51, 13 July 2010 (UTC)

I completely don't buy the idea that propellers are jet engines though, they don't produce a well defined jet. If you argue that propellers are jet engines, then other aircraft such as helicopters would also become 'jet aircraft'. Sorry, that's just not right. It's like that joke about how many legs does a dog have if you call a tail a leg? A: Four- just because you call a tail a leg doesn't make it a leg. ;-) - Wolfkeeper 22:51, 13 July 2010 (UTC)

Still, if you want to consider turboprops as hybrid jet engines, I guess that would be OK, it's similar to how Encyclopedia Britannica describes turboprops.- Wolfkeeper 22:51, 13 July 2010 (UTC)

As to turbofans, they do actually have a cold nozzle for generating a jet, or a similar arrangement (such as a mixer), so I'm pretty sure that they're still rightfully considered proper jet engines, rather than hybrids.- Wolfkeeper 22:51, 13 July 2010 (UTC)

I still don't think turboshaft are normally or correctly considered jet engines though.- Wolfkeeper 22:51, 13 July 2010 (UTC)

You're in a complete minority of one here. Consensus is to support a broad and inclusive article, as the most accessible, readable and most encyclopedic version. Turbojet, turbofan and turboprop should be included. Andy Dingley (talk) 23:03, 13 July 2010 (UTC)

Read it again, and say it again, if you still don't understand.- Wolfkeeper 00:55, 14 July 2010 (UTC)

• That was my mistake on scramjet cycles; I (erroneously, & curiously) decided to make shaft-work-out a requirement for that cycle. Ramjets are indeed Brayton-cycle derivatives. Heck, after a bit more thought, you could probably come up with a Brayton piston-cycle.
• I never suggested propeller-driven aircraft are jet engines. I was simply noting that they produce a "jet" of air as part of a systematic refinement of what a jet engine is and what it is not.
• Concerning the turbofan once again, it was never said it only had a hot-jet. Only that the primary difference between a turbojet and a turboprop is the fan has a duct/nozzle. Mixers are irrelevant.
• Turboprop/propfan engines obtain not an insignificant portion of their thrust from the hot-jet, and they do this by design. Also, they utilize the exact same cycle as a turbofan engine. Moreover, they are included in many texts and references alongside turbojets & turbofans under the heading of jet engines. Taken together, these support the case to include them under turbine-based jet engines. As for turboshaft engines (in aircraft application, that is), I don't think I would personally refer to them as a "jet engine." However: the engines themselves are identical to turboprops, and should at least have a (See also...) mention of them, perhaps at the end of a turboprop section. If someone asked me to give a 5 minute description of what a jet engine is, I would certainly mention turboprops/shafts.
• Lastly: the term "jet engine" clearly has multiple interpretations, at least when applied to aircraft jet engines; however, this article is very much "broad in scope." Considering that turboprops/shafts are often included with turbojets/fans, both technically and colloquially, it would certainly be a mistake not to mention them along with turbojets/fans while noting their differences (although I don't think they should be categorized under hybrids; it would differentiate them from turbojets/fans too much). Failing to mention them would, frankly, be un-Wikipedian: new readers would not be fully informed as to how broad the definition of 'jet engine' is, or the breadth of their applications; and it would not be balanced in the sense that many reputable sources include them as types of jet engines.

--GreyTrafalgar (talk) 14:09, 14 July 2010 (UTC)

In fact: "Turboprop engines may exert a significant part of their thrust by means of the hot-exhaust jet." (Hill & Peterson) --GreyTrafalgar (talk) 16:37, 14 July 2010 (UTC)

Proposed addition

Based on comments, I took SidewinderX's proposed addition, and made a few changes & additions of my own. Most people support a mention and brief explanation. Please critique; I have a habit of making things more in depth than need be.--GreyTrafalgar (talk) 16:37, 14 July 2010 (UTC)

Turboprop and turboshaft

Main articles: Turboprop and turboshaft

Turboprop and turboshaft engines are jet engine derivatives that extract work from the hot-exhaust jet to turn a rotating shaft, which is then used to produce thrust by some other means. While not strictly jet engines in that they rely on an auxiliary mechanism to produce thrust, turboprops and turboshafts are very similar to other turbine-based jet engines, and are often described as such.

In turboprop engines, a portion of the engines' thrust is produced by spinning a propeller, rather than relying solely on high-speed jet exhaust. As their jet thrust is augmented by a propeller, turboprops are occasionally referred to as a type of hybrid jet engine. While many turboprops generate the majority of their thrust with the propeller, the hot-jet exhaust is an important design point, and maximum thrust is obtained by matching thrust contributions of the propeller to the hot jet. Turboprops generally have better performance than turbojets or turbofans at low speeds where propeller efficiency is high, but become increasingly noisy and inefficient at high speeds.

Turboshaft engines are very similar to turboprops, differing in that nearly all energy in the exhaust is extracted to spin the rotating shaft. They therefore generate little to no jet thrust. Turboshaft engines are often used to power helicopters.

Propfan

Main article: Propfan

A propfan engine (also called "unducted fan", "open rotor", or "ultra-high bypass") is a jet engine that uses its gas generator to power an exposed fan, similar to turboprop engines. Like turboprop engines, propfans generate most of their thrust from the propeller and not the exhaust jet. The primary difference between turboprop and propfan design is that the propeller blades on a propfan are highly swept to allow them to operate at speeds around Mach 0.8, which is competitive with modern commercial turbofans. These engines have the fuel efficiency advantages of turboprops with the performance capability of commercial turbofans. While significant research and testing (including flight testing) has been conducted on propfans, no propfan engines have entered production.

Reference additions

• Hill, Philip; Peterson, Carl (1992), Mechanics and Thermodynamics of Propulsion (2nd ed.), New York: Addison-Wesley, ISBN 0-201-14659-2

I'd support that. I'd support it with or without propfan (propfans never really took off... and few people starting at the top-level entry wouldn't have started by searching directly for propfan. I'd even support it (should others insist) without turboshaft, as those are indeed significantly different. As here though, I think turboprop is an essential inclusion. Andy Dingley (talk) 16:45, 14 July 2010 (UTC)

Proposed addition has been added to the page. Turboprop & turboshaft were subsequently split into two sections, but as they are so similar, I recombined them (albeit with a better Main article link). As turboprops are not solely jet engines, and turboshafts even less so, it seemed to me and many involved in this discussion to be the way to go.

I put them in separate subsections. I am sorry, I did not know that there was this hugh discussion here about this, and I have not read it. I just thought it odd to have a subsection for all the other types while putting two together. However, I assume that the discussion above has considered this and many other aspects. Tomeasy _{T C} 16:29, 20 July 2010 (UTC)

Well, you won't hear any complaints from me about adding this content into the article. I had been thinking there should be a "formal" counting of votes for consensus before it's added... Wolf, you're the most vocal of the opponents to this addition, so if you would like a formal counting for consensus, just say so. -SidewinderX (talk) 18:07, 20 July 2010 (UTC)

Actually, I did not add, I just split content into two separate subsections. Tomeasy _{T C} 20:26, 20 July 2010 (UTC)

Turboprop, turbofan, and turboshaft engines are all 'jet engines' simply because they all utilise a turbojet as the core.

Small inconsistency

I think there is some scope for aligning these two paragraphs with each other: "Following the end of the war the German jet aircraft and jet engines were extensively studied by the victorious allies and contributed to work on early Soviet and US jet fighters. The legacy of the axial-flow engine is seen in the fact that practically all jet engines on fixed wing aircraft have had some inspiration from this design."

"Although German designs were more advanced aerodynamically, the combination of simplicity and advanced British metallurgy meant that Whittle-derived designs were far more reliable than their German counterparts. British engines also were licensed widely in the US (see Tizard Mission),and were sold to the USSR who reverse engineered them with the Nene going on to power the famous MiG-15. American and Soviet designs, independent axial-flow types for the most part, would not come fully into their own until the 1960s, although the General Electric J47 provided excellent service in the F-86 Sabre in the 1950s." JMcC (talk) 15:58, 6 January 2009 (UTC)

Whittle knew that an axial-flow engine would be superior but at the time he was developing his engine (1930s) axial-flow compressors were of abysmal efficiency, whereas the contemporary centrifugal compressors used in aircraft superchargers were fairly highly developed, with efficiencies approaching 90%. At the time it was difficult enough to build an engine that actually would run, Whittle himself stating that the turbine of the WU needed to extract around 3,000 hp just to run the compressor. At the time, there was no production piston aircraft engine that produced anywhere near this figure.

BTW, it wasn't just 'the combination of simplicity and advanced British metallurgy meant that Whittle-derived designs were far more reliable than their German counterparts' - it was that British engines had twice the power-to-weight ratio and half the specific fuel consumption of anyone else's engines.

The other difference was that the British engines were fully usable without delicate handling, as long as one kept the JPT down to below 300c then one could treat the engine as one would any other, the only limitation being a poor throttle response, a limitation of all early (and some current) turbojet engines. Other nation's engines (and the German ones in particular) had to be handled very carefully, careless handling leading to compressor stall (surging) or overheating of the turbine blades. Many of these other engines were liable to just explode randomly as parts failed, whereas this was a rare occurrence on British engines.—Preceding unsigned comment added by 86.112.61.204 (talk) 07:26, 26 July 2010 (UTC)

more advanced British Metallurgy?

Fallacious and specious un-NPOV. German metallurgy has always been decades ahead of British exactly like their mechanical adn civil engineering. The issue about reliability was solely result of unavailability of required metals for alloys- since Finland and Norway had been cut off (chromium, tungsten (known as Wolfram in Germany after its' discoverer). Martensite for example is a metallurgical phenomena named after its' German discoverer. I will amend the article to remove this erroneous NPOV.Starstylers (talk) 16:21, 11 April 2009 (UTC)

German metallurgy has always been decades ahead of British exactly like their mechanical adn civil engineering - Hmmm... Germany had to have the British come and build their railways for them though.

How was Norway cut-off? - Germany was occupying it for most of the war. The British had to ship their raw materials half way round the world, all the way from Malaya, much of-which was subsequently occupied by the Japanese, and they never had a shortage of raw materials for high-temperature alloys.

BTW, most of the different high-temperature alloys subsequently used in the early jet engines were developed for piston aero-engine use by Rolls-Royce in the 1930s, which is why so many of them have RR numbers in their designation. —Preceding unsigned comment added by 86.112.89.83 (talk) 13:50, 26 July 2010 (UTC)

Water jet help

Hey -- Does anyone have a decent reference for the basics of a water jet / pump jet? I have been working on converting the uncited table descriptions of the different jet engine types to cited prose descriptions, and I haven't been able to find a decent source for a water jet / pump jet. If anyone has a source, please go ahead and rewrite that paragraph. Or feel free to post it / link it here and I'll go ahead and do the rewrite. Thanks! -SidewinderX (talk) 11:52, 4 August 2010 (UTC)

von Ohain Literally Followed Whittle's Patent

The myth that von Ohain "didn't know" of Whittle's patent needs to be addressed. It is pervasive to the point that most people with some knowledge on the topic believe the Germans invented the jet engine in WWII. Not only did von Ohain know of the patent, it was published in a German magazine pre-war because Whittle didn't have the money to renew his patent. This was in fact the source of German knowledge on the topic. While von Ohain was either evasive, ambiguous, or later, outright dismissive regarding whether he was aware of the patent, all of the scientists debriefed post-war contradict his version of history. They freely commented that they referred to Whittle's work almost every day during their efforts. If someone here wants to continue with the fallacy of von Ohain's "independent" discovery, then the only acceptable reference would be one that specifically deals with Whittle's patent, how von Ohain could have been unaware of it, the debriefing of the other scientists contradicting his version of events, AND documents through time his independent "discovery". Perhaps some reference comment as well to the fact that Whittle's engines were functional and for that time relatively robust and therefore useful. All of the original German engines were highly experimental and wore out very quickly, not suited for production. The reason the Germans beat the British to the skys was that they recognized the import of the research and supported it. Whittle had very little support. This serves to further reinforce that the Germans began their research by making rough copies of Whittle's engines with the limited information they had at hand, rather than developing the technology de novo. —Preceding unsigned comment added by 84.74.110.16 (talk) 20:37, 1 December 2010 (UTC)

You need sources for Wikipedia. Which German magazine was the patent published in and are there any statements from any of the German developers confirming that they used it? Where is the "debriefing" documented? Chris55 (talk) 23:53, 1 December 2010 (UTC)

However, your assertion, Chris55, is at odds with the text in the article, which reads, "In 1935 Hans von Ohain started work on a similar design in Germany, apparently unaware of Whittle's work." The claim is then that von Hain had not studied Whittle's work and the evidence of his ignorance must be provided rather than the evidence for the debriefing document given that Whittle's paper had been published in a German magazine before the war. This would be the way modern scientific attribution would have it and very logically too: it's perverse to argue that Whittle's claim lies with proving that von Ohain was unaware of Whittle's work. Laetoli (talk) 01:25, 2 December 2010 (UTC)

Chris is correct. The claim that von Ohain is documented from an apparently reliable source, which also includes statements that Whittle's son doubted the claims, as noted in the notes. You need to provide reliable sources for the assertions you're making: taking the fact that WHittle's paper was published in Germany as proof that von Ohain must have been aware of WHittle's paper is synthesis - you need a reliable source that claims that. Further, as Chris menteioned, we must have reliable sources that assert that the German developers confirmed that they used it, and where this was confirmed. The burden of proof is on the person adding the information - the von Ohain claim is already cited - nothing needs to be "proved" there. - BilCat (talk) 03:16, 2 December 2010 (UTC)

As usual, the truth is probably more complicated than this week's BBC programme about Whittle, that I suspect the earlier contributor had also seen, makes out. Anthony Kay in his "German Jet Engine and Gas Turbine Development 1930-1945" says "When in 1934, [von Ohain] made a search through the patent records, it seems possible that he did not come across Whittle's patent of 1930, Guillaume's axial turbojet patent of 1923 or the Swedish Milo turbojet patents." His cautious statement does not exclude the use of Whittle's patent in the 5 years before 1939 but demonstrates the work being done in many countries: he draws attention to Anxionnaz's French patent of 1939 for a bypass turbojet. We need better sources.

But as with any invention, it is not only having the idea, but making it work that is crucial and the article currently doesn't sufficiently acknowledge that the British effort also produced results months after the German deployment. Chris55 (talk) 09:59, 3 December 2010 (UTC)

Edit request from 67.204.21.20, 10 December 2010

{{edit semi-protected}}

Hi, the inventor of the first jet engine propelled aircraft and jet engine is Henri Coanda with the Coanda 1910. Why is it not specified in the history section in your article? Have you been on NASA's site? Even they put it on there. This is intellectual property and not national pride, please modify correspondingly.

67.204.21.20 (talk) 20:06, 10 December 2010 (UTC)

There is currently a great amount of debate on this matter on Wikipedia. Take a look at the discussions over at Talk:Coandă-1910. I think we're waiting for the dust to hopefully settle before we make a decision about what is written here. -SidewinderX (talk) 20:19, 10 December 2010 (UTC)

The dust has apparently settled, with experts on both sides in conflict. Some experts say no way can the aircraft be the first jet because no evidence exists to prove that it flew, and others take Coanda at his word, accepting his description of the engine and the single test hop/flight. With that expert-level conflict firmly in place, WP:NPOV prevents us from stating one side of the conflict as fact. Binksternet (talk) 20:32, 10 December 2010 (UTC)

Hi, I'm going to close the edit request for now, as from a glance this appears to be a consensus-related issue. elektrikSHOOS 20:58, 10 December 2010 (UTC)

Given the POV pushing by this IP at Henri Coandă, I'd be very cautious in their edits anywhere near jet engines, real or imagined. Andy Dingley (talk) 21:57, 10 December 2010 (UTC)

If there's genuinely significant discussion about it by experts in the literature, then it probably should be mentioned/included. That's the Wikipedia way.- Sheer Incompetence (talk) Now with added dubiosity! 05:07, 11 December 2010 (UTC)

That's the problem: a lot of top level references which discuss early jet development do not mention the Henri Coanda experiment at all. Others refute it, and still others endorse it. There are three positions to take: pro, anti, and agnostic. Binksternet (talk) 05:30, 11 December 2010 (UTC)

One thousands years ago "top level references" were saying that the Earth is flat. The same with Coanda-1910; fifty years ago one controversial historian speculated that Coanda-1910 was not tested in December 1910. Now after 50 years Coanda-1910, the mainstream considers Coanda-1910 as the first jet-propelled aircraft. So the administrator should bear in mind what Jimbo told to all users of this Wikipedia tool.--Lsorin (talk) 09:15, 15 December 2010 (UTC)

• Flat earth a thousand years ago - no.
• Where is this "mainstream" claim for the Coanda jet? The people who have ever heard of Coanda's aircraft, let alone claimed it as a jet, are so far on the fringes that they're at risk of falling off the edges of your flat earth. The question of it being a jet has been beaten to death elsewhere, but you really cannot claim "mainstream" support for this. Andy Dingley (talk) 10:46, 15 December 2010 (UTC)

Raised at Wikipedia:Administrators'_noticeboard/Edit_warring#User:Lsorin_reported_by_User:Andy_Dingley_.28Result:_.29 Andy Dingley (talk) 11:19, 15 December 2010 (UTC)

So according to you Andy: Antoniu, Stine, Boyne, specialists at aviation proceedings [5], [6] several aviation museum around the world, and even the European Parliament are living on a flat Earth and only you, Binskternet and Gibbs-Smith "know" that Earth is round? My two cents: take a flight with a MIG-25 and you'll see that the earth is round and that BTW that plane is propelled by a jet engine!--Lsorin (talk) 15:16, 15 December 2010 (UTC)

Fluid

When I read the first line "A jet engine is a reaction engine that discharges a fast moving jet of fluid to generate thrust..." I thought this must be a mistake and nearly corrected fluid to gas, but I was careful and looked up Fluid first and was very surprised to see that fluids include gases now. I continued to read the article on Rheology were this was confirmed. Obviously gases do not exist anymore, only solids and fluids.

While this may be correct scientifically today I think we should take into consideration how people in general use the language. I have gone to school for 16-17 years, studying mainly scientific, technical subjects and math after the first half of schooling. I have read around 100 000 books of which 20% are about science, technology and math. But today is the first time in my life I have heard that gases are liquids.

I suggest we change the first line to read: "A jet engine is a reaction engine that discharges a fast moving jet of gas or fluid to generate thrust..." to make it easier to read for readers in general. I am sure readers in general know what I knew before I made this investigation today, that is: Most substances have three states, solid, liquid and gas, water, for example increases in temperature linearly to the energy supplied with two exceptions, when ice transforms into water a lot more energy is needed, the same happens when water is transformed into water vapor which shows that something fundamentally different happens when the temperature of water is raised from 99 Celsius to 101 Celsius than what happens when the temperature of water is raised from 97 Celsius to 99 Celsius.

The well-educated reader also knows that some substances, like Sulphur/Sulfur, goes directly from solid state to a gas through sublimation.

But we can not demand of the reader to be a professor of physics who is up to date on terminology.

To make the article easier to read, and to avoid thousands of corrections from fluid to gas which we will have to reverse, why not make it easier for the reader by using the expression "gas or fluid" instead of "fluid", which is not a direct fault, as both gases and fluids are fluids, and it fits much better with the understanding of readers in general. I hope we don't want to be snobs here in wikipedia and confuse people with very high level academic terminology, unless it is absolutely necessary (and in articles of academic level where the reader must be expected to be up to date on the latest developments in academic terminology). Roger491127 (talk) 12:35, 13 February 2011 (UTC)

How many paragraphs to explain that you don't know what a fluid is?

Add a footnote if you have to, but "gas or fluid" is tautological and we shouldn't dumb-down precision when it does give us any solid advantage as compensation. I'd even support reewriting as "gas" alone — although this changes the entire meaning of the definition (and excludes squid). As practical "jet engines" exist, in engineering terms, they rely on compressible fluids, i.e. gases alone. There's a reason why we have "gas turbines" as engines like this, but not "fluid turbines". Andy Dingley (talk) 13:13, 13 February 2011 (UTC)

Yes but jet boats (e.g. jet skis) also work by jet propulsion and are practical, and use turbines, and water isn't significantly compressible. As soon as you get away from jet engines not being an engine propelled by jet propulsion I'm pretty sure you've made a wrong turn, and a jet can form in just about any fluid.Rememberway (talk) 15:40, 13 February 2011 (UTC)

Jet boats don't use jet engines though, nor do they have turbines (Excluding the handful of water speed record boats that do indeed use jet engines or gas turbines). A "jet boat" or pump jet is a piston engine (sometimes a turboshaft gas turbine) driving an impeller in a duct, with an exhaust jet. The engine and jet drive are quite separate, linked by a drive shaft. It would be most unhelpful to describe these as "jet engines" (as this article currently does), even if we regard them as "jet propulsion". Clearly they are jet propelled, but using the broad term "jet" for them is difficult, as it invites confusion with the pre-existing concept of "jet" in the minds of most readers (i.e. a gas turbine reaction jet engine). Wording around articles like that is difficult, but fortunately this article as jet engine is very clearly outside that situation and we should move the pump jets outside it.

I think that by that argument motorjet isn't a jet engine either.Rememberway (talk) 15:56, 19 February 2011 (UTC)

Motorjet only has one reference in it, and even that's wrong! Caproni Campini N.1 is a rather better article. A motorjet is a jet engine, although not a gas turbine. It generates thrust by burning fuel in a duct, and this duct is pressurised by a separate engine. The thrust-generating duct is still transforming fuel into thrust, the mark of an "engine" in this sense. Andy Dingley (talk) 17:13, 19 February 2011 (UTC)

Right, so you agree that gas turbines are unnecessary for the definition of the scope of the article, so I'm sure you'll agree that ramjets are jet engines. And there is the slightly sticky point that even water is somewhat compressible, but we'll ignore that. But there's two screw cases; Project Pluto and the aeolipile, both are commonly described as jet engines, and do not involve combustion.Rememberway (talk) 19:25, 19 February 2011 (UTC)

Both of those still involve the conversion of heat energy into motion. The pump jet does not. Andy Dingley (talk) 19:42, 19 February 2011 (UTC)

There's two different definitions of 'jet engine': jet engine. You either take the more general one, which is an engine that emits a fluid jet for propulsion, or you pick the airbreathing one involving hot air. Because encyclopedias try to cover a topic encyclopedically I think most people agree that we're better off taking the more general one here, because it subsumes the other anyway; and it's not like much of the article is used discussing rockets and pumpjets, the maths and behaviors are essentially the same or extremely similar, so we are able to cover the whole lot without any difficulty.Rememberway (talk) 00:28, 20 February 2011 (UTC)

After consulting the wikipedia article on Gas, where nowhere is mentioned that gas is a fluid, and the NASA web site where the word gas is used thousands of times I changed the first sentence into:

A jet engine is a reaction engine that discharges a fast moving jet of gas or fluid to generate thrust by jet propulsion

see http://www.ueet.nasa.gov/StudentSite/engines.html for a justification for this change.

We cannot exclude 99.9% of the readers by using formulations which may be scientifically correct but totally confusing to everybody except for a few thousand scientists. And the formulation "gas or fluid" is not incorrect, if gas is a fluid, I am just giving two well known names of what comes out of a jet engine. If somebody wants to explain that strictly scientifically all gases are fluids he can insert a note and explain that, with good references for his statement, of course. Roger491127 (talk) 08:53, 19 February 2011 (UTC)

WP is not a WP:reliable source, especially not for propagating definitions into other WP articles.

"Gas or fluid" is tautological, but that's a minor linguistic note, not a technical error. However claiming that jet engines include jet boat drives would be (they're a separate unit, driven by an engine, not an engine themselves). So would it be to claim that a ducted fan with a non-jet engine (like the Coanda-1910) is a "jet engine". The only known types of jet engine (which includes gas turbines and ram jets, but not, as discussed above pump jets) rely on the compressibility of a gas. There aren't any jet engines that use a non-gas fluid, so it's simply unnecessary to state "gas or fluid", when "gas" alone is a perfectly adequate statement, both technically and linguistically.

Should an article on "jet engines" include pump jets and rockets? Can a case be made that these are both "jets" and "engines", thus "jet engines"? Of course those statements have some truth to them, but that doesn't make them a useful scope for defining a useful article! Thinking that just because the shortest statement of a definition would fail to exclude some of the obviously distinct and separate types, these types should then be added to an article is not only pedantic, but also makes for bad and confused articles. Andy Dingley (talk) 12:10, 19 February 2011 (UTC)

It doesn't seem to be a bad article.Rememberway (talk) 15:03, 19 February 2011 (UTC)

I note that the German and French encyclopedias define jet engine the same way we currently do. Although I hear your words, I admit it doesn't sit well with me that knowledge could/should be different in different countries, and the equations and behaviors for the different sorts of jet propulsion seem to be extremely similar across the different types.Rememberway (talk) 15:56, 19 February 2011 (UTC)

I think that if you get away from defining jet engine as something that works by jet propulsion then you're dumbing the article down, and I think that Wikipedia needs the topic to be bigger to ensure its overall coverage.Rememberway (talk) 15:56, 19 February 2011 (UTC)

I see someone has reverted back to "fluid" instead of "gas or fluid". I will not get into a revert war. I can just argue for the formulation "gas or fluid". Don't you think readers in general will think it must be wrong to write fluid when there are two pictures of fast flowing gas right beside the text?

Most people in the world have learned that matter can be in one of three states, solid, liquid and gas. Some have also heard about a fourth state, plasma.

Extremely few think that what comes out of a airplane jet engine, or a rocket, is a fluid. Even NASA explains how a jet engine works using the word gas. So if you want to use the word fluid it is at least necessary to explain that both gases and fluids are considered to be fluids when we talk about jet engines. Of course we should not dumb down wikipedia, but we cannot turn our backs to 99.9% of the readers, and a lot of authors working for NASA, and hundreds of millions of teachers who teach pupils about the 3 states of matter, plus the 4th, plasma. I referred to, among several other sources, the wikipedia article about Gas, but I could have referred to millions of text books on physics which say the same as that article. Please, somebody, change it back, or explain in the article why gases are fluids. Roger491127 (talk) 15:33, 21 February 2011 (UTC)

As, in practical terms, far too many readers confuse "fluid" with "liquid", then we'd be better with just "gas", especially in the lead. Andy Dingley (talk) 15:45, 21 February 2011 (UTC)