Talk:Jet engine/Archive 4

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Rockets - really?

The section on Jet engine#Rocket states "The rocket engine uses the same basic physical principles as the jet engine for propulsion via thrust, but is distinct in that it does not require atmospheric air to provide oxygen." By contrast the article lead states, "A jet engine is a reaction engine discharging a fast-moving jet that generates thrust by jet propulsion. This broad definition includes airbreathing jet engines (turbojets, turbofans, ramjets, and pulse jets) and non-airbreathing jet engines (such as rocket engines)." Now, a rocket cannot both be distinct from the jet engine (per the associated section) and also a form of jet engine (per the lead). This contradiction needs to be resolved. Every source that I have ever seen treats them as distinct. But then, I have never read any advanced textbooks on the thermodynamics of jets and rocketry. Is the sub-classification of a rocket as a type of jet a genine one from sufficient reliable sources to be justifiable or is it mere editorial sophistry? — Cheers, Steelpillow (Talk) 03:18, 23 June 2018 (UTC)

Looking back to the discussion on Fluid from several years back, this concern was raised then and no consensus for the current state emerged. The idea that a pumpjet is also a jet engine is of equal concern. As I see it, jet propulsion and a jet engine are different things. Most people know that squids and octopuses are jet-propelled when in a hurry, but nobody suggests that the muscles they contract to squeeze water backwards amount to a jet engine. Similarly a pumpjet does not generate mechanical power within itself but is just an example of a ducted propulsor requiring a mechanical drive of some description, so it cannot itself be an engine. What about rockets? Like I say, every RS I have ever seen distinguishes the rocket engine from the jet engine and both WP:COMMONSENSE and WP:COMMONNAME would suggest that we take the same approach. Given the uncertain outcome of the older thread and the lack of immediate interest in this one, I will be bold and start making changes accordingly. — Cheers, Steelpillow (Talk) 13:43, 24 June 2018 (UTC)
In fact, with that understanding the article on the Airbreathing jet engine should be merged back into this article, as there is no real distinction any more. — Cheers, Steelpillow (Talk) 14:09, 24 June 2018 (UTC)
We have another article, solely because this article was too long. The article, which you apparently want to make, already exists. If we merge it back in, this article will be too long again. GliderMaven (talk) 04:33, 1 July 2018 (UTC)
I'm sorry, but I reverted your inconsistent changes, it's trivial to source that rocket engines work by jet propulsion and we're defining a jet engine as an engine that works by jet propulsion. If you want to do something like this with two long standing articles you need to have consensus with someone other than yourself.GliderMaven (talk) 20:33, 24 June 2018 (UTC)
Thank you for replying. But the points I make above already meet your objections. We already have an article on Jet propulsion, so another one on that subject is not needed here. Just because a device works by jet propulsion does not mean that it is a jet engine: yes, jet engines work by jet propulsion but they are not the only mechanism available: do you seriously hold that a squid or an octopus in a hurry must contain a jet engine? Yes, we already have the article on airbreathing jet engine, but you seem to have missed the bit where I suggest an article merge. Would you prefer the present article to be merged into Jet propulsion? I have less argument with that. — Cheers, Steelpillow (Talk) 20:54, 24 June 2018 (UTC)
Also, the article has for some time stated that "The rocket engine uses the same basic physical principles as the jet engine for propulsion via thrust, but is distinct". Quite how you can claim that there is a "consensus" to the opposite is not clear to me. I edited the article for consistency on this point, not for inconsistency as you also suggest - you are mistaken there. — Cheers, Steelpillow (Talk) 10:16, 25 June 2018 (UTC)
Rocket engines are not jet engines and do not belong here. They are a form of jet propulsion, and belong in that article, but this is an article about engines, the engineering actualisation of a concept, not the principle underlying it. There is also the aspect that (see langue and parole for the linguistic discussion of this) the term "jet engine" in an article title may be (and is) validly a place-marker for a more complicated and specific term: one that implies certain aspects of "what is a jet engine" and the article is not improved by a game of hanging as many tenuously-related additional terms on there as possible. Andy Dingley (talk) 10:37, 25 June 2018 (UTC)
Agreed. Given the lack of engagement from elsewhere, I have edited the article accordingly. — Cheers, Steelpillow (Talk) 14:47, 27 June 2018 (UTC)
Not only is this absolutely not agreed but we already have the article on airbreathing jet engines which is apparently what you're trying to turn this article into. We do NOT need two articles on exactly the same thing with different titles!!! If you want to change the names, petition for that. If you want to merge the articles, petition for that. But what you can't do is just change both articles to be the same damn thing.GliderMaven (talk) 15:45, 27 June 2018 (UTC)
Agreed. The article on rocket engines cites Sutton & Biblarz in stating that rocket engines are a form of jet engines, so at least one respectable textbook defines things that way. Perhaps other experts define things differently, and in that case it would be good to note there are several definitions. Whichever way we decide to split up the text it would be good to check that there isn't too much overlap between articles. Martijn Meijering (talk) 16:32, 27 June 2018 (UTC)
@Mmeijeri: That appears to be an editorial slip. The cited source does not make the claim stated in the article, at least not that I can see. It says only that "Rocket propulsion is a class of jet propulsion", and nobody is disputing that: see Andy Dingley's "langue and parole" explanation above for its significance to the present article. — Cheers, Steelpillow (Talk) 16:49, 27 June 2018 (UTC)
I don't understand the difference. Rocket propulsion is a form of jet propulsion, rockets are engines so I'd say that makes rocket engines jet engines. The organs squids use to propel themselves are not generally considered engines, which would appear to exclude them from the definition of jet engines. Perhaps this is not how aeronautical engineers see things, but it isn't obvious to me that that is the case. I don't particularly care either way, but let's make sure we follow the commonly accepted technical definition. And suppose we did remove rocket engines, do you propose that the present article should be merged with that on airbreathing jet engines? Martijn Meijering (talk) 18:53, 27 June 2018 (UTC)
Nevertheless, squids are held to move by jet propulsion even though they do not contain jet engines. Thus, jet propulsion cannot be synonymous with jet engines. Aeronautical engineers universally (to my knowledge) describe jet engines, rocket engines and ducted propulsors as distinct, while many (but not all) also describe them all as forms of jet propulsion. So there absolutely is a commonly accepted distinction between jet propulsion and the jet engine and a related commonly accepted distinction between the jet engine and the rocket engine. And yes, that merge is exactly what I hope to propose in due course. — Cheers, Steelpillow (Talk) 19:31, 27 June 2018 (UTC)
In reply to GliderMaven, the issue of any merge is contingent on whether or not the article topics are effectively the same. As I originally pointed out, the present article is internally inconsistent on that score, hence the need to clarify its scope as a first step. Meanwhile, if you have concerns over my behaviour, please bring them up on my talk page and do not inflict so many exclamation marks or shouty capitals on the other participants here. — Cheers, Steelpillow (Talk) 17:17, 27 June 2018 (UTC)
I agree with Steelpillow and Andy Dingley, and disagree with GliderMaven and Martijn Meijering. Saying "we define" jet engines as including rocket engines is original research in the absence of reliable sources which say so. Sutton & Biblarz has been shown to be a verification failure. Saying WP:Other stuff exists or "that's the way it is" does not establish a consensus. I just checked my 1974 college Aerospace Propulsion textbook and an older one written in the 1950s by Joseph Foa, and nowhere do they call rockets "jet engines"; they are reaction engines.
The following articles are affected:
  • Jet engine – Text still includes rockets as a class; this must be removed. Rockets should only be mentioned by way of comparison.
  • Airbreathing jet engine – is redundant to Jet engine, and is improperly (redundantly) titled. (Page size=37,831; 4,071 views in 30 days) Should be merged into Jet engine (page size=75,105; 28,205 views in 30 days) and kept as a redirect, (or deleted?).
  • Rocket engine – Again, should not imply that rockets are a type of jet engine.
Submitting an RFC might be a good idea, except I have no idea how to write one neutrally (Let's hear it for another Wikipedia Catch 22! :-). We also run the risk that might not succeed in establishing a consensus. Perhaps we should concentrate on proposing the merge of Airbreathing jet engine into Jet engine. JustinTime55 (talk) 13:30, 28 June 2018 (UTC)
@Mmeijeri: Can I ask whether you still agree with GliderMaven, after what has been said since? — Cheers, Steelpillow (Talk) 16:16, 30 June 2018 (UTC)
I have no strong feelings either way, I just want to make sure that we follow the commonly accepted terminology among aeronautical engineers. If a narrower interpretation is in use, then that's fine. If it turns out more than one classification scheme is in use, we can say so. That said I'm a bit sceptical. The interpretation you make of Sutton sounds forced and sounds like WP:OR. I'm not an aeronautical engineer, but I own a few textbooks, so I'll have a look at what they say. If we end up merging the articles, that's fine with me, but let's make sure we don't lose any valuable material. Maybe it can be moved to other pages. Martijn Meijering (talk) 16:29, 30 June 2018 (UTC)
I see you have unilaterally removed the phrase that included rocket engines in the broad definition of jet engine. According to WP:BRD that's not what we're supposed to do while we're still discussing the change. Martijn Meijering (talk) 17:21, 30 June 2018 (UTC)
Thanks for the swift reply. I did not interpret Sutton, just quoted from it. It was the claim (now removed) in the article and which you drew our attention to that was OR. My own view comes from other sources and I have added a couple of citations to the present article section on the Rocket to help make that clearer (Kermode specifically treats rocket propulsion as distinct from jet propulsion, with a separate section for each). I think the source of confusion may arise in the fact that "jet propulsion" is defined in different ways, see for example the Collins dictionary online definition. This makes it easy for editors to mix and mash incompatible statements. Whether a rocket is included under "jet propulsion" or not, that is a matter for the relevant articles, it is definitively not a "jet engine". And we are not defining jet propulsion here, we are defining the jet engine. The following tree diagram is my own concoction, but I am not aware of any RS which contradicts it. I don't know if it helps.
        Reaction (physics)      =     Reaction engine     Other reaction mechanism
                |__________            ______|__              _______|______
                |          |          |         |            |              |                   
          Jet propulsion   |    =     |    Jet engine     Pump-jet     cephalopods,
                |          |          |                               insect larvae,
                ? (Alt Df) ?          |                                    etc.
              Rocket propulsion = Rocket engine
If content is lost from here, it will be because it belongs in neither of the merge candidates. Nor does it add anything to the main articles it relates to. And it will remain in the page History anyway, from where it can be recovered for re-use elsewhere at any time. So you need have no fears on that score.
WP:BRD is an optional guideline supplement and is inconsistent (by design) with others such as WP:3RR. If you have any problems with my behaviour, please take them up on my talk page, not here. — Cheers, Steelpillow (Talk) 17:49, 30 June 2018 (UTC)
I don't think it is correct to describe cephalopods or their propulsion organs as reaction engines as they are not engines. Cephalopod *propulsion* can be accurately described jet propulsion however. As for Sutton, sorry but my interpretation is simply the natural prima facie one, and if you think he means something else (quite possible) the onus is on you to prove it. But I'm not sure it matters. I've tried to find an authoritative source online that makes an unequivocal statement either way, without much success, except for Sutton. I've found a US Navy manual that does so (it considers rocket engines a type of jet engine), but that's not a good enough RS. I've asked an acquaintance who is an aeronautical engineer. To him the term jet engine has always implied air breathing, although he also suggested that rocket exhaust can be considered a jet. My current personal impression is that while some experts (probably not all, but including Sutton) may technically consider rocket engines a type of jet engine, and may use the term that way when discussing general principles, but will in practice in most other contexts use the unqualified word jet engine for airbreathing systems and use the more specific term rocket (or whatever specific system they're discussing) for other systems. If that's true, then I'll be happy to support a merger. Any left-over material can then perhaps be moved to the rocket or jet propulsion article. Martijn Meijering (talk) 19:13, 30 June 2018 (UTC)
Good point about the cephalopods, now modified.
Please forgive me but when I write "I did not interpret Sutton, just quoted from it", I cannot see how that suggests I "think he means something else". On the contrary, I think it means exactly what it said, that "Rocket propulsion is a class of jet propulsion". The book does not appear to say anywhere that "rocket engines are a class of jet engine", and it is WP:OR of you, this time, to claim that it means that. Kermode is/was very much a mainstream expert and his treatment is flatly contradictory to your interpretation. Here is a more recent one: Douglas R Taylor; Boxkite to Jet: The Remarkable Career of Frank B Halford, Historical Series No. 28, Rolls-Royce Heritage Trust, 1999. Chapter Ten discusses among other things "jets, turboprops and rockets" (p.123). Note the flat distinction between "jets" and "rockets". Nowhere in the ensuing pages does Taylor suggest otherwise. Then I checked my fairly extensive source material on HOTOL, its RB545 engine and their respective successors Skylon and SABRE. Lots of "hybrid", "dual-cycle", "like a jet in airbreathing mode then like a rocket" and, as time passes, it eventually becomes established as a dual-cycle air breathing rocket engine (that's what the ABRE in SABRE stand for). Absolutely nowhere is it described as a dual-cycle or hybrid "jet engine". Enough of logic-chopping and wikilawyering. This discussion has now reached a point where all the RS points one way and anybody who disagrees with edits to that effect will have to produce their own RS to back up their claims, BRD or no. — Cheers, Steelpillow (Talk) 20:19, 30 June 2018 (UTC) [Updated with SABRE et al 23:26, 30 June 2018 (UTC)]
Your ideas are clear and simple. However writing encyclopedia articles is complex. As H. L. Mencken once stated: "For every complex problem there is an answer that is clear, simple, and wrong.' GliderMaven (talk) 04:33, 1 July 2018 (UTC)
The article is not specifically about the aeronautical term 'jet engine'. We already have another article on that exact topic called Airbreathing jet engine. And the reason we have that is because this article was too long, and was split, 8 years ago. And, no, it wasn't split because the rocket engine stuff making it too long, the airbreathing jet engine article is pretty long in it's own right, and there's only about two paragraphs on rocket engines in this entire article, and there's loads and loads of paragraphs on everything else. Apparently these two paragraphs offend you in some way? GliderMaven (talk) 04:33, 1 July 2018 (UTC)
We potentially could just rename the articles 'jet engine' -> 'jet propulsion engine' and 'airbreathing jet engine' -> 'jet engine' except you would then have to go through all the links and change them over. But it's all cosmetic, we already define the term 'jet engine' in the exact way you prefer in the second paragraph, and there's an entire article on the exact topic you want, as well. GliderMaven (talk) 04:33, 1 July 2018 (UTC)
Really, in my opinion, instead of ranting on the talk page of this article, your time would be much better spent smartening up airbreathing jet engine, a topic you appear to be professing love for. There's no rocket engines there, I promise. GliderMaven (talk) 04:33, 1 July 2018 (UTC)
Your opinion is inconsistent with every RS yet produced. You do nothing here but revert my edits and post a rant at me before going away until next time. That is not constructive discussion, it is obstruction. You have now reverted that edit three times in all. Please do not oblige me to take this to WP:AN/3RR. — Cheers, Steelpillow (Talk) 08:42, 1 July 2018 (UTC)
I asked very early on whether some kind of article reshuffle would help, so it is good to see you at last acknowledging the possibility. Perhaps at some point you can also acknowledge both WP:OTHERSTUFF and the merge comments above. If you think that this article is about something other than the subject of its title, then what exactly do you think it is about and how does that differ from the reaction engine and from jet propulsion? What would you call it? — Cheers, Steelpillow (Talk) 09:06, 1 July 2018 (UTC)
I'd call it you not revert warring and actually getting consensus, like I already asked for above. All I'm seeing at the moment is you revert warring and threatening people. Continue to do that, and I will call on everyone to revert your edits out of hand. Cut that shit out, and we'll talk. GliderMaven (talk) 15:35, 1 July 2018 (UTC)
It was not me who reverted you just now, but another editor. Your rant here is a gross breach of WP:NPA but I am prepared to pass it over if they have managed to get the message through to you. — Cheers, Steelpillow (Talk) 19:26, 1 July 2018 (UTC)
You're truly a brilliant person, you know? Can I ask if you're offended by the entire existence of rocket engines, or only that they are ever mentioned in this article??? GliderMaven (talk) 22:41, 1 July 2018 (UTC)

Outlet Mach number

Operation of the air inlets and air flow patterns through the J58

In this edit, GliderMaven changes the text to say that supersonic exhaust is a requirement for supersonic flight. This is entirely wrong, and the (sourced!!) statement was correct (although awkwardly phrased) before. Exhaust Mach number and flight Mach number are completely different — high gas temperatures massively increase the local speed of sound. I’d fix the edit but the page is currently protected. Ariadacapo (talk) 05:55, 5 July 2018 (UTC)

The original was definitely very wrong, or at minimum highly deceptive, in every particular. There is a context here, which is jet engines. No jet engine has a subsonic exhaust under normal operating conditions; they have to choke to get any efficiency at all. To state that convergent nozzles can be subsonic, not in this context. In addition the SR-71 at mach 3.0, I have no clue how anyone can think that was operating with a convergent nozzle at mach 3.0. As you can see from the diagram, at the very least beyond Mach 1.5, the aircraft is running with a condi nozzle configuration. You can quibble about the transonic regime. While the new phrasing can be further improved, there is no world in which the original 'was correct' about anything. GliderMaven (talk) 16:13, 5 July 2018 (UTC)
The edit appears to be a bit of a "curate's egg", good in parts and bad in others.
The claim made in it, and reasserted above, that a convergent nozzle flow is necessarily Mach 1 appears to be false: "the exit velocity depends on the nozzle pressure ratio and the nozzle total temperature.","Although the jet velocity Vj must be larger than the aircraft velocity V0 to generate useful thrust, a large jet velocity that exceeds flight speed by a substantial margin can be very detrimental to propulsive efficiency. Maximum propulsive efficiency is approached when the jet velocity is almost equal to (but, of necessity, slightly higher than) the flight speed. " It is, as was previously stated, at or below Mach 1.
On the other hand, the first of the sources just cited supports the edit in stating that for supersonic exit flow a con-di nozzle is necessary, so that correction is welcome.
Might we be able to declare an honourable draw? — Cheers, Steelpillow (Talk) 17:13, 5 July 2018 (UTC)
The problem is not a quibble about which flight speed mandates con-di nozzles. The problem is that flight Mach number depends on the flight speed and the speed of sound outside (mainly air temperature), while exhaust Mach number depends on the speed and speed of sound at the exhaust plane (mainly exhaust temperature). These are completely different flows. Mach 1 for the airplane’s nose is not the same speed as Mach 1 in the exhaust gas. The text now associates both regimes as if they were the same. Ariadacapo (talk) 06:28, 6 July 2018 (UTC)
Suggested fix:
“Convergent nozzles are only able to accelerate the gas up to local sonic (Mach 1) conditions. To reach high flight speeds, even greater exhaust velocities are required, and so a convergent-divergent nozzle is often used on high-speed aircraft. (ref Gamble 2004)”
Ariadacapo (talk) 07:29, 6 July 2018 (UTC)
I have no problem with that. — Cheers, Steelpillow (Talk) 21:35, 6 July 2018 (UTC)

Protection

I have protected the page from editing as it appears that users are edit warring rather than coming to a consensus here. Suggest that you come to some agreement here before the article is released for editing, thanks. MilborneOne (talk) 19:57, 1 July 2018 (UTC)

This article is now the subject of a merge discussion - see below. The protecting admin, MilborneOne (talk · contribs), appears to be off-wiki for the last two days and counting.

Please could an admin add the following to the head of the article: 

{{mergefrom|Airbreathing jet engine|discuss=Talk:Jet engine#Merge proposal|date={{CURRENTMONTHNAME}} {{CURRENTYEAR}}}}

There is also a WP:UNPROTECT request outstanding.

— Cheers, Steelpillow (Talk) 12:51, 11 July 2018 (UTC)

 Done added box. @MilborneOne: I don't see this being part of the warring, but if you disagree feel free to revert without consultation. Best regards, — xaosflux Talk 15:30, 11 July 2018 (UTC)
Article is protected again, I released it on the understanding that there would not be a return to edit wars, if it happens again it will be treated as disruptive editing. It will be released again when a clear consensus has formed, thanks. MilborneOne (talk) 18:32, 12 July 2018 (UTC)
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