Talk:Lift (force)/Archive 9

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Newtonian lift and the circulation theory

I just came across this:

"At the outset it may be set down that any defect in the [Newtonian] theory is due, not to any want of exactitude in the fundamental theory - this rests definitely on the third law of motion and is absolute - but rather to the difficulty and uncertainty as to its manner of application in real fluids."

— Lanchester; Aerodynamics (1907), Page 5:[1]

This very much bears out what I have been saying above, that the Newtonian model is not so much wrong as difficult to analyse (to identify "the air" deflected downwards). Lanchester goes on to expand his Newtonian flow model (that we have been likening to a firehose) to include some germ of the circulation theory of lift (see his Sections 160 and 161 in the above link). This expansion is key to the way the discussions here have gone: Lanchester does not treat the firehose as wrong, just as in need of much elaboration. A later controversy did erupt, between a British establishment elaboration based on perturbations (i.e. ignoring Lanchester from here on) and a German establishment elaboration based on circulation. Lanchester's words suggest to me that this controversy was not over the validity of the Newtonian model, but rather over its elaboration. As it happens, the perturbation model lost out and the circulation model survived into modern times - along with its Newtonian underpinning, as is well cited in the article. The controversy is documented in: Bloor, D; The Enigma of the Aerofoil: Rival Theories In Aerodynamics, 1909-1930, University of Chicago (2011). Sadly I do not have time to read it all, as apart from the first chapter (Haldane and the ACA for those who care) it is off my current line of work. Perhaps it may contradict what I suggest above, I don't know. Meanwhile, I think that all this might provide useful food for thought into whether the structuring of this article could be improved and whether we are putting the right emphasis in the right places. — Cheers, Steelpillow (Talk) 20:41, 12 March 2015 (UTC)

Checking back, I am not sure how far Lanchester goes towards a recognisably modern circulation theory, but it does not affect the rest of what I have said. [Updated 21:22, 13 March 2015 (UTC)]

Bloor (referenced above) tells an interesting story. In an idle moment I found extracts at Google Books, here. In discussing Berriman, he writes; "The basic formula is Force = Mass x Acceleration, but how is this formula to be applied? What is the mass of air that is involved? The original Newtonian picture [Billiard-ball mechanics - SP] must have underestimated this mass, hence the underestimation of the lift that can be generated. Berriman suggests that..." and goes on to describe the "sweep" model (our "firehose"). Later, he describes how Lanchester took this as one of the key starting points from which he evolved his circulation theory of lift. — Cheers, Steelpillow (Talk) 11:15, 18 March 2015 (UTC)

Yes, and the key to this "starting point" for Lanchester (in the early 1890s!) was when he realised how utterly IMPOSSIBLE is the "sweep + downwash" model. It was only when Lanchester completely abandoned that line of thinking that he made progress and proposed CToL. (Zapletal) 101.171.85.77 (talk) 01:11, 19 March 2015 (UTC)

I'm glad to see that there's now some question in Steelpillow's mind whether "we are putting the right emphasis in the right places".

That said, what he says here still accords the "Newtonian model" too much importance in the overall scheme of things. The CToL won out because it makes accurate predictions of how upwash and downwash are distributed in the field, and how the imparting of downward momentum is different for different subsets of the air, things about which the firehose is just plain wrong. CToL and the firehose share a Newtonian "underpinning" in the sense that they both make use of NII. A key difference is that CToL applies NII correctly (taking the pressure field into account as one of the forces acting on "the air"), and the firehose does not. Getting from the firehose to CToL goes far beyond any reasonable meaning of the word "elaboration". It requires throwing out key assumptions of the firehose, i.e. that only a finite stream is affected by the foil, and that there is no direction change upstream of the foil. Zapletal is right that the "sweep" model wasn't really a "starting point" for CToL. J Doug McLean (talk) 23:34, 20 March 2015 (UTC)

Tie-in between "Momentum balance in lifting flows" and "some of the air"

Under "Flow deflection and Newton's laws", the passage "Some of the air passing the airfoil has downward momentum imparted to it at a rate equal to the lift. (See 'Momentum balance in lifting flows' for details)" implicitly promises that the issue of "what air" is so affected will be clarified in the later section. In the current version of "Momentum balance in lifting flows", the reader would have to be very technically astute to make the connection. The paragraph I proposed adding:

Thus it is found that the change in momentum flux from upstream to downstream accounts for the entire downward force $-L'$ exerted by the airfoil only in the case of the tall, slender rectangular control volume. For control volumes of other shapes, the integrated pressure difference between the top and bottom offsets some or all of the $-L'$ exerted by the airfoil, and the change in momentum flux is between $-L'$ and zero.

would help the reader make the connection. But now I think that directly referring back to the earlier section would be even better:

The simplified explanation of lift given in "Flow deflection and Newton's laws" states that some of the air passing the airfoil has downward momentum imparted to it at a rate equal to the lift. The analyses described above show that the region of air for which this is true is the tall, slender rectangular control volume. For control volumes of other shapes, the integrated pressure difference between the top and bottom offsets some or all of the $-L'$ exerted by the airfoil, and the change in momentum flux (the rate at which momentum is imparted )is between $-L'$ and zero.

I have posted this proposed wording in my User:J_Doug_McLean/sandbox, where it can be viewed in context. I hereby propose that this paragraph be added to the article. J Doug McLean (talk) 01:42, 24 March 2015 (UTC)

Observations and a Suggestion on How to Go Forward

I have not been a regular participant in the discussions on this talk page, but I have been here from time to time. I first came here to close an RFC on The Statement, and I see that another RFC is in process concerning whether to provide a quantitative or a qualitative statement. I have taken another look and have a few observations. On the one hand, this is a purely technical topic, and so should not result in as much controversy as, for instance, American politics. On the other hand, this is a purely technical topic with a considerable amount of controversy, both because of its complexity, and because there are alternate technical formulations, and academic issues about which formulation to use (or both). The controversy about this article spilled over to WP:ANI in a very poorly handled thread. The editors here are normally civil, but are frequently divided about content.

I would suggest that the editors all read or re-read the dispute resolution policy. It points out that disputes include content issues and conduct issues. The issues here are, fortunately, primarily content issues. (ANI wasn't, in my opinion, necessary or appropriate.) I would then suggest that, for this article, the appropriate way forward might be formal mediation by a member of the Mediation Committee. Formal mediation is a slow process, but the issues about this article have gone on for months and will go on for months, so why not spend the months with a mediator working to help the editors communicate to improve the article?

Robert McClenon (talk) 16:56, 22 March 2015 (UTC)

Thank you for the suggestion, Robert. I had thought about it. My concern is that this is not solely a content issue, 99% of it is just being disguised as one. I joined this discussion when one editor came to the Aviation WikiProject already feeling thoroughly jaded and asked for a fresh pair of eyes. I did find behavioural issues at first and had to quell the more abusive aspects. It soon became crystal clear that the discussion was being kept alive by a lone editor who is trying to present his own version of the truth and not the picture to be found in the reliable literature. His main weapons are vast screeds of techno-verbiage and tenacious persistence. He swamps every discussion (e.g. the RfC above) and it gets hard for visitors to these discussions - dare I say it, such as your good self - to see past it. It appears on the face of it a perfect case of long-term WP:DISRUPTION through WP:RUNAWAY to the talk page. His attitude to myself and others has been, "fine, as long as you agree with me," soon followed by, "If you don't agree with me then you are one of the enemy." I am under no illusion that he will listen to a formal mediator any more than he has listened to the rest of us, mediation will simply be seamlessly integrated into part of the drip-fed disruption. It will only be when this editor is removed from the discussion and can no longer drown it out that the content issue can be properly addressed. However, if you still feel that an experienced mediator can resolve this situation, I would be willing to give it a try. — Cheers, Steelpillow (Talk) 18:20, 22 March 2015 (UTC)

Herein is the root cause of the problem. Steelpillow says "It soon became crystal clear that the discussion was being kept alive by a lone editor who is trying to present his own version of the truth and not the picture to be found in the reliable literature." This statement, as with many others like it from Steelpillow, is UTTERLY FALSE. This is easily confirmed by the most fleeting scan of the last three Talk pages. These show that there are at least TWO people here who are strongly opposed to the TS-PoV. At least three, if the article's long time contributor Mr Swordfish is also included, and who was recently described by Steelpillow as "...newly befuddled".

It is worth noting that the people most strongly opposed to TS are those with the deepest understanding of the technical issues (ie. of "the picture found in the reliable literature"). In contrast, the two, and only two, people who strongly support TS have themselves acknowledged that they have negligible understanding of these technical matters. They have also shown that they are only aware of a very small fraction of the many RSs covering this field.

Steelpillow has a track record of "edit-warring". It is he who has been most persistent with his particular brand of WP:DISRUPTION, which includes the frequent use of the sort of falsehoods given above. Mediation may help him see this. (Zapletal) 101.171.255.242 (talk) 00:46, 23 March 2015 (UTC)

Steelpillow's description of how the discussion was "at first" being "kept alive" is quite reasonable. In fact he joined the discussion on 22 September. Zapletal didn't subsequently comment until 27 November. Since then, Zapletal has reignited it on occasion as well. Attacks on editors' failing memories do not work on Wikipedia. Burninthruthesky (talk) 10:38, 23 March 2015 (UTC)

I disagree with his history, especially the part about me being "thoroughly jaded" when I asked for assistance at the aviation project. Here's the diff: https://en.wikipedia.org/w/index.php?title=Wikipedia_talk:WikiProject_Aviation&diff=prev&oldid=626611902 - As can be easily seen, it's a very neutral request for more eyes on the issue. I think it is correct that at one point Doug was the lone holdout, but that is no longer the case. It took me several months and many re-readings to finally understand his point, but once I took the trouble to understand it, it's a very reasonable point. Mr. Swordfish (talk) 15:33, 25 March 2015 (UTC)

I'm sorry Mr. Swordfish. I have no dispute with you, but I am having trouble understanding.

Any revision that presents a more complicated explanation first will not have my support. 21:45, 30 May 2014 (UTC)

My own preference is to just leave it out and move on. 17:15, 10 November 2014

So, do we treat rate of momentum change? The AAPT thinks we should. 14:51, 11 November 2014

Can you explain the reason for your changes of heart? Burninthruthesky (talk) 17:16, 25 March 2015 (UTC)

I eventually figured out what Doug was on about. I just didn't understand it at first.

BTW, I don't see any contradictions among the three quotes above. Mr. Swordfish (talk) 19:17, 25 March 2015 (UTC)

When you continued to emphasize your original argument for following the AAPT advice, I got the impression the only reason for your preference to leave it out was that you wanted some peace and quiet (I know I did, but I also wanted a fair outcome). Thank you for clarifying your position. Burninthruthesky (talk) 07:30, 26 March 2015 (UTC)

@Mr swordfish: My apologies if I have misrepresented you. It was a long time ago. I do recall at least one editor being thoroughly jaded at the time I came in, but it seems I mixed two of you up in my memory. I confess that I had not noticed you previously either say that you fully accepted Doug's point or argue unequivocally in its favour - you had not done so at first. Again, I am happy to stand enlightened. — Cheers, Steelpillow (Talk) 19:16, 25 March 2015 (UTC)

For me, conduct is the primary issue. A large part of the discussion seems devoted to constructing a false narrative about the opponents of poorly-justified change, by misrepresenting their views, followed by WP:IDHT towards any attempt at clarification. Once again I am alluded to as, "people who strongly support TS". I don't. I do, however, strongly support Wikipedia policies such as WP:CONSENSUS and WP:CIVILITY.

I regret that the previous ANI discussion was derailed by miscommunication. I still don't know whether those not deeply involved in this discussion don't agree that misrepresenting the views of others is against policy, or they choose to WP:IAR in order to keep a published author on board, or they cannot penetrate this discussion to see where the misrepresentations can be found. I appreciate Robert's constructive suggestion, although I too am unsure whether mediation would help with this. One thing I do know is that I don't have time for a full-scale repetition of the previous discussion. Burninthruthesky (talk) 10:38, 23 March 2015 (UTC)

What we have here includes a very knowledgeable editor, User:J Doug McLean, who is an authority in the field. However, it appears that there are two different technical ways of describing lift that are significantly different, and the expert uses one of them, and the other one is more widely used. If that is not the case, please clarify. We have at least two active editors who prefer the other approach. We also have an active but unregistered editor whose constructive contributions to this article are negligible, but who engages in personal attacks against critics of the expert. Robert McClenon (talk) 15:23, 23 March 2015 (UTC)

If that is not the case, please clarify. I think you basically have it right, but allow me to elaborate anyway: there's a simple way to explain lift that is understandable by almost anyone after reading a few paragraphs (or less) : air is deflected one way, the wing experiences a force in the opposite direction according to Newton's laws. There is also a much more precise mathematical treatment that requires understanding of partial differential equations, vector fields, conservation of mass, energy, and momentum, the principle of superposition, the Kuta Condition etc. This rigorous presentation is what you find in engineering texts with perhaps a brief mention of the simple explanation. The two are quite consistent with one another as they are just different ways of looking at the same problem. The current consensus (as evidenced by the state of the article for the last five years or more) is to present the simpler non-quantitative explanation first and proceed to give the more elaborate explanation. I don't think that's in dispute at the moment, other than including a quantitative statement as part of the simple explanation (i.e. the topic of the current RFC) Mr. Swordfish (talk) 16:02, 23 March 2015 (UTC)

Right. The debate isn't about the qualitative explanations versus the quantitative science. It's about what to include in the qualitative early section of the article. I have been opposed to including the quantitative statement (dp/dt = -L, in shorthand) along with the qualitative explanation because it is inappropriate in that section of the article and because the issues involved are complicated such that the oversimplified version is misleading. The debate is also about what weight to give to one body of sources (mostly non-specialist) versus specialist sources from the mainstream of aerodynamics. J Doug McLean (talk) 02:49, 24 March 2015 (UTC)

I would make some small clarification to the content issue. Both explanations are widely used, sometimes together, to introduce the subject. Having done so, the explanation espoused by our expert is the one more relevant to deeper technical analysis. Our expert believes that the other explanation at best overstates its case and in its barest form is just plain wrong. The rest of us, whatever we may think of it, accept that if it is reliably sourced then we should include it in the form, and with the due weight, that we find in the sources. — Cheers, Steelpillow (Talk) 18:24, 23 March 2015 (UTC)

Robert, your claim that I am someone "whose constructive contributions to this article are negligible" is deeply offensive. For the record I have brought a great deal to the article, including numerous RSs of the highest standard, and much technical rigour. The RSs include Lanchester (the originator of CToL and the Principle of No Momentum), Bryan (who directly refuted Berriman's version of TS), and many others such as Stokes, Kelvin, Helmholtz, Rayleigh, Lamb, Klein, Betz, Glauert, Durand, Bloor, etc., that some of the other editors were apparently not aware of, but who have made major contributions to this field. Technically I have clarified a great deal, although I accept that much of that has fallen on deaf ears. Please refrain from making any more WP:PERSONAL attacks. Please strike-through your above offensive remark. (Zapletal) 101.170.85.69 (talk) 01:33, 25 March 2015 (UTC)

"...two different technical ways of describing lift ... If that is not the case, please clarify." (<- McClenon). "The two are quite consistent with one another..." (<- Mr Swordfish). No. The pictures presented by CToL and TS are utterly incompatible. CToL presents the picture shown in the animation used in the article, which is remarkably similar to real flows, as proven by countless experiments. TS presents the picture shown in the "One Minute Physics..." cartoon at the very end of the article, which is as Bryan described it "physically speaking, an impossibility". The two pictures are as incompatible as Heliocentric-Round-Earth and Geocentric-Flat-Earth theories. (Zapletal) 101.170.85.69 (talk) 01:33, 25 March 2015 (UTC)

Zapletal: I don't care if you are a professional mind-reader and therefore you know for a fact that Steelpillow and Burninthetruthsky are maliciously telling lies. Even if you know that as an absolute fact, Wikipedia policy says that stating that other editors are telling untruths is a personal attack. Cease and desist from the personal attacks, or you can be blocked or banned from editing. Robert McClenon (talk) 15:23, 23 March 2015 (UTC)

Robert, can you please clarify your statement that "...Wikipedia policy says that stating that other editors are telling untruths is a personal attack". Can you please refer me to the appropriate policy page, and also comment on whether there is any inconsistency there? Specifically, can you show me where it says that it is perfectly acceptable for an editor to claim that there is only one other editor supporting a particular edit, when in fact there at least two, but it is considered totally unacceptable to bring such an arithmetical error to light? If this is in fact so, then what is the correct protocol for addressing such erroneous claims? (Zapletal) 101.170.85.69 (talk) 01:33, 25 March 2015 (UTC)

Zapletal, I came here because of a request to have this talk page protected. While not spelt out as such at Wikipedia:No personal attacks it has long been considered that accusing others of lying is a personal attack. Even when you can provide differences that would seem to show you are correct. If you think someone has made a statement that you think is incorrect is to Wikipedia:Assume good faith and just take the stance that they might have just made a simple error. Provide the necessary differences and just state that you think they are in error. I would prefer not to protect the page, but given that you change IPs I will if you continue attacking others. CambridgeBayWeather, Uqaqtuq (talk), Sunasuttuq 09:09, 27 March 2015 (UTC)

CBW, you say "Provide the necessary differences and just state that you think they are in error." That is exactly what I did (given that, IMO, "false" is an acceptably polite synonym for "in error"). The fact that you are now threatening to prevent me posting here, even though I have done nothing wrong as "spelt out" in Wikipedia policy, and have instead been doing my best to correct the numerous "errors" here, suggests that this whole Wiki system is heading down a very slippery slope. As a good example of the hypocrisy and double standards we are dealing with, please look at the recent edits in the "Rotary Wings" section below. Steelpillow is repeatedly deleted parts of my post (something he has done a great deal of in the past) on the basis of "personal attack", even though said text being deleted is a direct quote taken from one of Steelpillow's own personal attacks on another editor! This censorship of facts under the feigned guise of maintaining "Civility" will only lead to low quality articles. Is that what you want? Please read about WP:RANDY. (Zapletal) 101.170.85.65 (talk) 01:14, 28 March 2015 (UTC)

(PS. The discussion about the Moon being made of WP:GREENCHEESE sounds awfully familiar. PPS. I note that Robert has still not made right his personal attack on me... (Zapletal)) 101.170.85.82 (talk) 02:13, 28 March 2015 (UTC)

My main question is, again, whether the various editors are willing to try something else, namely, formal mediation. We have seen that discussions at this talk page get nowhere. Do we want to try mediation, or do we want to continue to have discussions that get nowhere? It doesn't appear that the two other active editors are about to go away. They have been here for months and continue to complain about being ignored. Mediation won't take any longer than the current conflict has been going on. Robert McClenon (talk) 15:23, 23 March 2015 (UTC)

I have no objection to formal mediation, although I have to say I don't really know what is involved. I mooted the RFC in an effort to reach closure on the Statement, but I think we (ie the editors on this page) have bigger issues than that and that the problems with civility and communication will continue after the RFC is settled. At this point it appears that some editors have let their emotions get the better of them. Agree that this is almost entirely a content dispute and that if we can all keep our cool we will work our way through it. Thanks for your assistance. Mr. Swordfish (talk) 16:08, 23 March 2015 (UTC)

I would welcome formal mediation provided a mediator can be found who has a background in the field and is thus in a position to understand what the various sources say about the theoretical issues in question. J Doug McLean (talk) 02:49, 24 March 2015 (UTC)

Made the formal request

I have filed the formal request for mediation at Requests for Mediation. Robert McClenon (talk) 03:10, 24 March 2015 (UTC) It is my understanding that the next step, within 24 hours, is that a bot will notify us that I have filed the request. Robert McClenon (talk) 03:11, 24 March 2015 (UTC)

Thanks Robert. I've accepted at Wikipedia:Requests for mediation/Lift (force). I fixed a red link to User:Mr swordfish. I hope the bot will pick up the change in due course. Burninthruthesky (talk) 08:31, 24 March 2015 (UTC)

I've accepted, but my participation may be constrained by my being away from internet access for most of April.

I've read the "policy" and "guide" pages on mediation, and it's not clear to me how this is supposed to work. I see that, so far, Robert McClenon and Steelpillow have described the dispute only in very brief terms on the request page. Question: Is this the level of detail on which the Mediation Committee will make its accept/reject decision? And another question: If the committee accepts the case, will we be expected to present our arguments on the project talk page, or is the committee expected to read our arguments on the article talk page?

I assume that other editors wishing to participate in the mediation may register on the request page at Wikipedia:Requests for mediation/Lift (force). J Doug McLean (talk) 18:45, 25 March 2015 (UTC)

All of the editors whom I identified have agreed to mediation. There are a few other conditions, such as that there must have been discussion on the article talk page, which there has been. Based on previous experience, further discussion will be on the mediation project page, and then the mediator will provide instructions as to how the discussion should be conducted. It is my understanding that other editors who read the article talk page may join in the discussion. I think that any further instructions on how the mediation proceeds will be provided by the mediator. Robert McClenon (talk) 18:52, 25 March 2015 (UTC)

I understand mediation cannot proceed whilst the RFC is open. See Wikipedia:Requests_for_mediation/Christian_terrorism#Decision_of_the_Mediation_Committee for a previous example. Burninthruthesky (talk) 07:33, 26 March 2015 (UTC)

I am aware that informal mediation cannot proceed while an RFC is open. If formal mediation cannot proceed, then I will let the mediator request that the originator of the RFC withdraw the RFC in favor of mediation, since mediation is another way to address long-standing content issues. Robert McClenon (talk) 21:34, 26 March 2015 (UTC)

Since User:Mr swordfish originated the RFC in order to address the long-standing content issue, I will request that he request closure of the RFC if it is a block to mediation. Robert McClenon (talk) 21:36, 26 March 2015 (UTC)

RFC - Should we keep the current quantitative statement on momentum transfer in the second section or replace it with a qualitative version?

The following discussion is an archived record of a request for comment. Please do not modify it. No further edits should be made to this discussion. A summary of the conclusions reached follows.

This has been one of the best RFC's I have closed to date. The comments at the end in the "Compromise Statement" have made closing this much easier, as until that time it was very close for all options. The consensus is to "Combine". There was no consensus on a combined version, I am sure it will be worked out. AlbinoFerret 03:49, 12 April 2015 (UTC)

---

Should we keep the current quantitative statement on momentum transfer in the second section or replace it with a qualitative version?

Mr. Swordfish (talk) 15:40, 9 March 2015 (UTC)

Background:

J Doug McLean wrote: I'd like to see a fresh straw poll on the issue of whether we should keep the current quantitative statement or replace it with a qualitative version like the one in my sandbox.

I think the time is ripe for an RFC. Please reply with keep or replace and whatever summary you'd like to include for your reasoning. Please keep the the discussion civil and on-topic. See WP:RFC for details on this process.

For reference, here's the relevant excerpt from Doug's sandbox:

The air flow changes direction as it passes the airfoil and follows a path that is curved downward. According to Newton's second law, this change in flow direction requires a downward force applied to the air by the airfoil. Then, according to Newton's third law, the air must exert an upward force on the airfoil. The overall result is that a reaction force is generated opposite to the directional change.

Here's what the current version of the article says:

Some of the air passing the airfoil has downward momentum imparted to it at a rate equal to the lift. (See "Momentum balance in lifting flows" for details) This is consistent with Newton's second law of motion which states that the rate of change of momentum is equal to the resultant force.

Mr. Swordfish (talk) 15:40, 9 March 2015 (UTC)

I thank Mr. Swordfish for taking this action. Since editors new to this topic have been invited to comment, I think providing them background in addition to the candidate texts would be good. Previous discussion on the talk page has covered many pages, and most of it has been archived. It would be difficult for a newcomer to discern the key points of the arguments. I think we should post brief summaries of the pro and con arguments. I'm willing to draft my side, if that would be appropriate.

J Doug McLean (talk) 17:22, 9 March 2015 (UTC)

If this was in "the intro section," I would strongly state that it should be qualitative not quantitative. However, it is not, and seems to be mis-characterised here. It is in the first actual explanation section, the subsection called 'Flow deflection and Newton's laws.' This comes after the introductory section to the main section called 'Simplified physical explanations of lift on an airfoil,' which itself comes after an introductory section called 'Overview', all of which come after the actual 'intro section' - normally called the lead - which appears above the contents. How can you call this 'the intro section'??! --Nigelj (talk) 18:05, 9 March 2015 (UTC)

I have re-cast the RFC to say "second section" rather than "intro section". Hope it's not too late. Apologies for the confusion. Mr. Swordfish (talk) 19:36, 9 March 2015 (UTC)

>Since editors new to this topic have been invited to comment, I think providing them background in addition to the candidate texts would be good.

Agreed. Herewith, a brief synopsis:

As part of a major re-org last August, a quantitative statement about momentum transfer was added to the article. At the time it stated: The resulting force upwards is equal to the time rate of change of momentum of the air deflected downwards. This impetus for adding it was an article published by the American Association of Physics teachers which said: "At least for an introductory course, lift on an airfoil should be explained simply in terms of Newton’s Third Law, with the thrust up being equal to the time rate of change of momentum of the air downwards." (http://scitation.aip.org/getpdf/servlet/GetPDFServlet?filetype=pdf&id=PHTEAH000037000005000297000001&idtype=cvips&doi=10.1119/1.880292&prog=normal)

This addition provoked a rather lengthy and sometimes acrimonious discussion, of which a main focus was what is meant by "the air" in the statement. Eventually, the editors reached consensus/compromise on the current wording. Consensus can change, hence this RFC.

I'm trying to keep this synopsis as neutral as possible, and I'm not sure I can provide further details while maintaining neutrality. I'll have more to say by way of background in my response. Disclosure: I authored both the original statement from August and the compromise/current statement. Mr. Swordfish (talk) 20:04, 9 March 2015 (UTC)

• Keep The case for the quantitative statement is simple: it is widely prevalent in reliable sources, several of which are cited in the article. It does not matter what we editors believe, Wikipedia expects us to present the mainstream view, and in this it puts verifiability and due weight above what we believe to be true. The case against the quantitative statement is, by contrast, hollow. The debate itself has been running solidly for well over a year (I got bored trawling the archives), and in all that time nobody has ever cited a single reliable source discussing any controversy over the quantitative statement, as required by WP:FRINGE. One source has been offered, but it was written by the sole registered wiki editor arguing against the quantitative statement, and thus he has a clear conflict of interest in this debate. The only other voice against it has been an IP editor, who will be unable to join us for a week since this page has been semi-protected by an Admin who determined that this editor has been overly abusive. All remaining sources proffered against the quantitative statement have turned out to be the editor's interpretation and not the words of the source itself. Of course, if new sources can be brought forward that might change things, but for now at least there is simply no encyclopedic case for the quantitative statement's removal. None. — Cheers, Steelpillow (Talk) 21:00, 9 March 2015 (UTC)

Partial rebuttal of "Keep" The above misrepresents the case that has been made in favor of the change. First, it misrepresents the situation regarding the published sources. The proposed replacement does not discuss any fringe theory or any controversy, and so the WP:FRINGE requirement that the sources explicitly discuss a controversy does not apply. The sources quoted in the current version of this section make a quantitative statement (i.e. that downward momentum is imparted to "the air" at a rate equal to the lift) that is supported only in one special case and is otherwise contradicted by the more rigorous analyses in the sources from the mainstream aerodynamics literature cited in the later section "Momentum balance in lifting flows". Finding a contradiction between two groups of sources, even though no controversy is explicitly mentioned in any of them, and assessing the relative authoritativeness of the sources based on their scientific rigor, is permissible, in keeping with Due and undue weight. And the assertion that my own book is somehow central to the case that has been made is unfounded. Finally, the assertion that only two voices have been raised against the quantitative statement is untrue. In December one other editor posted a long discussion finding The Statement to be "problematic", and in February another found the statement confusing (with good reason) and suggested a replacement that was qualitative. Substantive objections to the current passage itself are given below. J Doug McLean (talk) 03:52, 10 March 2015 (UTC)

Different groups of sources present different bases for analysis, they reach different conclusions yet there is no evidence of controversy. The conclusion must be that overall they illuminate a consistent theory. Let me restate, whether any editor sometimes gets confused or has problems understanding the debate is quite beside the point. The sources speak for themselves, and we must not stand in their way. — Cheers, Steelpillow (Talk) 11:39, 10 March 2015 (UTC)

Steelpillow's arguments here flout simple logic and Wikipedia policy. True, there is no mention of a "controversy" in any of these sources, but no one has advocated that it be presented as one in the article. There is clearly a contradiction between the two groups of sources, and thus the conclusion cannot be that "overall they illuminate a consistent theory". The statement "The sources speak for themselves" is meaningless. All published sources speak for themselves, simply by being published. But that doesn't mean we should give them all equal prominence. Per Due and undue weight, this is a situation in which we shouldn't. J Doug McLean (talk) 19:40, 13 March 2015 (UTC)

• Replace The case for replacing the statement is based on article structure and a correct understanding of the physics as found in the preponderance of published sources.

The statement in question is not in an "intro" section, but it is in a prominent place near the top of the article (There are only five short paragraphs ahead of it), in a subsection of the major section titled "Simplified physical explanations of lift on an airfoil". Given its placement in the article structure, a qualitative version is more appropriate than a quantitative one, especially given that the oversimplified quantitative version is problematic, as argued below.

By referring to "some of the flow" instead of just "the flow", the current wording, in a legalistic way, avoids being outright wrong, but it still gives a misleading impression. The reader is likely to infer, and reasonably so, that the downward momentum that is imparted all shows up as downward momentum in the flow downstream of the foil. But in fact, half goes to canceling upward momentum that was imparted ahead of the foil, and only half shows up downstream. To have the wrong impression corrected, the reader would have to read the rather technical later section "Momentum balance in lifting flows". But why introduce a wrong impression at all in an early section that is supposed to be simplifying things?

Of the sources cited in support of the current version, only two present any supporting analysis, and that analysis is based on an idealized flow model (I call it the "firehose model") that is at variance with the actual physics and with the methods used in the mainstream literature, in ways that have been discussed at length on this talk page. In contrast, the mainstream analyses cited in "Momentum balance in lifting flows" use a model that they rigorously show is physically correct. Thus the current version gives undue weight to a view of the physics that is not mainstream, and, in fact, satisfies the definition of a fringe theory. J Doug McLean (talk) 03:52, 10 March 2015 (UTC)

The encyclopedic case for getting rid of the oversimplified quantitative statement is clear. This is not a case where the sources are such as to force us to choose verifiability over truth. This is a case where appropriately weighting the different sources allows us to have both. J Doug McLean (talk) 16:10, 10 March 2015 (UTC)

These arguments make the case for keeping very well. They corroborate the points that different sources using different bases for analysis reach different conclusions, and with no evidence of controversy. Undue weight suggests that all be presented faithfully in the article. Several are bundled together in the discussion of "Momentum balance in lifting flows", one is of a rather different character and so presented in a summary of "Flow deflection and Newton's laws." However the argument for removal is then suggesting that WP:UNDUE endorses the burying of one particular approach, a clear fallacy. — Cheers, Steelpillow (Talk) 11:39, 10 March 2015 (UTC)

I was just looking at Electron#Atomic_theory to see how the article handles the difference between shell-theory and quantum theory. Both models are presented in separate sections right next to each other, without any discussion of one refuting the other. Can we learn anything from the approach taken there? Burninthruthesky (talk) 11:00, 11 March 2015 (UTC)

Is this the "firehose model" in [2] Lanchester §160? Burninthruthesky (talk) 22:28, 10 March 2015 (UTC)

A problem with drawing an analogy between Electron#Atomic_theory and our article is that while the two theories in Electron#Atomic_theory differ in their detailed modeling, their major predictions don't contradict or refute each other, in contrast to our case, in which one group of sources claims dp/dt = -L for "the air" without qualification, which is contradicted by the results from two of the three ways of defining "the air" examined by Lissaman. So I'd say that giving two models equal billing is more appropriate in the case of Electron#Atomic_theory than it is in our case.

Yes, Lanchester's §160 discusses a model that is essentially equivalent to the "firehose" model we've been discussing. But in §160 Lanchester is not so much advocating for the model as showcasing its shortcomings, concluding in the final sentence of §160 that "the hypothesis is insufficient". Then in §161 he emphasizes the importance of including the effect of the upwash ahead of the foil, something that is completely ignored in our other sources' versions of the "firehose". J Doug McLean (talk) 19:43, 13 March 2015 (UTC)

• Comment The proposed change would remove material supported by five citations. That may not be immediately obvious from the plain-text quotes above. Burninthruthesky (talk) 10:48, 10 March 2015 (UTC)

Actually, six of the sources cited in this section mention the quantitative statement dp/dt = -L in one way or another:

• Clancy: Here the analysis presented in support of the statement is based on the "firehose model", a model that doesn't actually substantiate the statement, but simply assumes it a priori. The "firehose model" also assumes, without justification, that the only force acting on "the air" is the force exerted on it by the foil.
• Three papers from one non-specialist journal (AAPT): Waltham also bases his analysis on the "firehose model". Swartz cites Waltham. Smith couches dp/dt in terms of m delta v/delta t, without saying how single values of m and v can be assigned to an infinite, non-uniform flowfield, unless what he has in mind is the "firehose model". All of these assume, without justification, that the only force acting on "the air" is the force exerted on it by the foil.
• Berriman: This citation is in dispute (see talk page section immediately above this one) because it makes an erroneous version of the statement, ascribing dp/dt = -L to "a stratum of air", a body of air for which Lissaman showed that dp/dt = 0.
• Lissaman: This is the only one of the six whose analysis meets the standards of mainstream aerodynamics analysis, by assuming a realistic form for the flowfield and properly taking into account the pressure field as exerting one of the forces acting on the air.

What Lissaman shows is that the rate at which momentum is imparted to the flow is affected by the pressure field and is different for different subsets of the air. The picture presented by the other five sources is thus misleading and not representative of mainstream aerodynamics.

Actually, Lissaman is cited in this section only because the qualifying wording "some of the air" would have no support without him. J Doug McLean (talk) 19:47, 13 March 2015 (UTC)

• Combine The current contains the relevant quantitative, cited section, the proposed is better written. Incorporating the quantitative rate into the proposed would leave the article clearer with the same accurate information. SPACKlick (talk) 12:04, 10 March 2015 (UTC)

• Replace and move quantitative statement to later in the article. First, I'd like to say that reasonable people can disagree on this. There are definitely two sides to this argument and I would encourage everyone to try to understand both.

In favor of keeping the quantitative statement, there is the American Association of Physics Teachers (AAPT) who recommend "...lift on an airfoil should be explained simply in terms of Newton’s Third Law, with the thrust up being equal to the time rate of change of momentum of the air downwards.". This pedagogical recommendation is what persuaded me to include the statement in the article when doing the major re-draft last August. Moreover, there are several other sources that can be cited to back the assertion L = dp/dt.

So, including the quantative statement seemed like a slam-dunk. L=dp/dt is easily derivable from Newton's second law F=ma, (all you need to do is substitute L for F and rewrite ma as dp/dt), AAPT recommended it, and the statement has numerous cites to back it up, what could go wrong?

Well, the problem lies in what is meant by "the air". Clearly, it can't mean all of it since the net momentum change for a plane in straight and level flight is zero and therefore the momentum change for the air must also be zero to comply with conservation of momentum. I was unaware of control volume analysis when I included the statement last August, but upon further research it turns out that dp/dt depends on the shape of the region - that is, if you take a square region, integrate the momentum change over that region, and take the limit as the size of the square goes to infinity, then dp/dt = L/2, or one half of the lift. If you take a long flat horizontal rectangular region instead of square you get dp/dt=0. It's only when you employ a tall thin vertical region that you obtain dp/dt = L.

In short, the quantitative statement is only true for a very specific region of "the air" and not true for most sections. In particular, it is not true for most of the reasonable interpretations of "the air" that the readers might assume.

The upshot after all this is the carefully worded intentionally vague current verbiage: Some of the air passing the airfoil has downward momentum imparted to it at a rate equal to the lift.

This statement is technically true (or at least verifiable) in a legalistic sense and is well supported by the cites, so there is nothing in Wiki policy that would require its removal. But verifiability is a necessary but not sufficient criteria for inclusion. We editors must consider the experience of the reader and present an article that is logically well-organized and presents the material in a straightforward easily understandable manner. Ultimately, this is what determines my opinion here - what makes for a better article from the readers' perspective? It's not about being "right" or "wrong" or one side "winning".

My take is that the current quantitative statement is a bit awkward and intentionally vague due to its having to "write around" some complex details to be technically correct. The vagueness begs the question of what is meant by "some of the air". I could see someone putting the equivalent to a tag next to it. By contrast, the suggested replacement text is straight-forward and easily understandable. Since this is a very early section of the article that is aimed at the lay-reader, I don't think a quantitative statement is necessary. I don't have a particular antipathy to including a quantitative statement in this section, but thus far we have been unable to craft one that is clear and straightforward enough for my liking. To reiterate, this is an editorial judgment call and I respect the opinions on the other side.

One "tipping point" for me was this thread where one of the editors (Mark.camp) discusses "...what I as an ordinary (non-expert) consumer find to be confusing about the current text,...". My take is that if editors are confused about the material then the readers will also be confused. Much earlier, another editor (0x0077BE ) questioned "...why we're bringing momentum into this at all." (https://en.wikipedia.org/w/index.php?title=Talk%3ALift_%28force%29&diff=626659376&oldid=626659076)

All that said I will not be unhappy if keep is the outcome upon closure. But my editorial judgement is that the material is clearer and more easily digestible to the intended audience if the quantitative statement is removed from the current section and integrated into the momentum transfer section. Mr. Swordfish (talk) 21:18, 11 March 2015 (UTC)

I'd like to suggest that this post is an excellent demonstration of why the only way to navigate this minefield of editorial opinion is to stick to what the reliable sources actually say and not to try and interpret them (this is of course enshrined in the WP:NOR policy, especially WP:SYNTH). It is not for us to opine on what "the air" might be. mark.camp (talk · contribs) described himself as "an ordinary (non-expert) consumer", yet this post from some time ago is consistent with a slightly more knowledgeable status. So what the ordinary non-expert might see may or may not be what has been suggested. For my part I would suggest that the immediate question, "which air?" needs a great deal of analysis to answer and it may or may not spring a surprise. But it does not negate Newton's laws of motion as applied to lift, it just complicates things. This is just another reason to roll with the judgement of the many reliable authorities who have published on this topic - and that means keeping the quantitative aspect, although I do like the suggestion of SPACKlick (talk · contribs) to borrow the more readable phrasing. — Cheers, Steelpillow (Talk) 22:27, 11 March 2015 (UTC)

Steelpillow's take on the question "which air?" reaches the opposite of a logical conclusion. The deliberately vague "some of the air" is bound to raise the question in the minds of some readers. Whether they're non-experts or experts is beside the point. And how our readers are likely to take something is legitimately our concern as authors and editors. The question itself, i.e. what body of air has downward momentum imparted to it at the rate -L, is not a question that "needs a great deal of analysis to answer" or that has any surprises in store. We have a citable answer from Lissaman: dp/dt = -L for any tall rectangular column, of any horizontal width, as long as the horizontal width is a small fraction of the vertical height. Note that the shape is specific, but the size is non-unique. So the answer is a bit technical, and the current wording misleads by giving the impression that it's simpler than it really is. The suggested replacement solves this problem by avoiding the question all together, and it is just as well supported by sources as the current wording is. J Doug McLean (talk) 19:58, 13 March 2015 (UTC)

• Keep in some form We must put the most understandable explanations WP:UPFRONT, and make the article accessible to a wide WP:AUDIENCE. To that end Mr. Swordfish brought the suggestion that we follow the educational guidance from the AAPT, and I haven't seen a stronger argument than that.

There is a valid question as to whether the current description of "some of the air" could be confusing. I actually think this is too specific about leaving something explicitly undefined. If this were a fresh discussion I might have suggested removing "some of", but that isn't moving towards agreement. I'm happy to go with whatever consensus is determined. Burninthruthesky (talk) 09:08, 12 March 2015 (UTC)

REPLACE - At stake here is whether Wikipedia can ever be considered a genuine Encyclopaedia, or merely a random collection of citations and PoVs. The Lift article currently presents two very different and incompatible explanations of Fluid Dynamic Lift, with no explanation given for this incompatibility.

1. On the one hand there is "The Statement", which is presented both near the very top of the article, and also several times in the bottommost External Links. That is, TS is in the most read sections of the article. TS presents a picture of a horizontal onset flow in front of the aerofoil, and then an ever descending "downwash" behind the aerofoil. It is indisputable that TS presents this picture, because it is exactly this picture that accompanies so many presentations of TS (eg. see last External Link "One Minute Physics...").

2. On the other hand there is the "Circulation Theory of Lift", which is presented in the middle, more technical, parts of the article. CToL presents a picture of horizontal flow at large distances from the aerofoil, with only the local flow rising in a symmetric "hump" near the aerofoil. This picture is well depicted by the animation next to the section - "The airfoil affects the flow...".

Importantly, the TS-picture is utterly unrealistic. Real Lifting flows do not look anything like it. This was pointed out by Lanchester 120 years ago, and by many others since (eg. see Bryan's quote in the Berriman section above, which describes TS flow as "physically speaking, an impossibility"). Conversely, the CToL picture of Lifting flows has been shown to be accurate to within all experimental tolerances (when adjusted for details such as viscosity, turbulence in the onset flow, etc.).

Put simply, TS is analogous to a "Flat-Earth-at-the-Centre-of-Universe" theory, with CToL being the "Round-Earth-Orbiting-the-Sun" theory. It is worth noting that Flat-Earth theory can be considered to be a "good enough" approximation at small scales, perhaps when laying out the foundations of a house or drawing a street map of a small town. But NO good Encyclopaedia presents its Geology or Cosmology sections with a Flat-Earth-at-Centre-of-Universe introduction. At least not without some qualification of just how wrong such a view is. With regard to Lift, TS-theory is not accurate at any scale, so can never be said to be a "good enough" approximation. It does nothing but give an entirely misleading picture of the essence of Lift.

If TS is kept in this Lift article, then Wikipedia can abandon all pretence at being a genuine Encyclopedia. It will be more of a Wackypedia, where any and all wacky fringe theories can be paraded as encyclopediac knowledge, just as long as some editors can find a few obscure citations to support their PoVs, and are obstinate enough to force those PoVs through.

Note, of course, that this would just be a case of history repeating itself. The Ancient Greeks held the Round-Earth heliocentric view during their Golden Age, until it was eventually subverted by the Flat-Earth geocentric religious views. A thousand years of Dark Ages followed, and then a long climb out of that hole. Any editors with a sense of responsibility are reminded that future generations will reap what you now sow. (Zapletal) 101.170.42.154 (talk) 01:06, 18 March 2015 (UTC)

• Replace. I'm not saying this because of policy or anything. It's just that Doug's version simply explains how lift works better. In fact based only on that explanation I already understand in general terms how lift works, and don't feel the need to read the 'momentum balance in lift flows' section (which I'll say takes a lot more brainpower to understand). The paragraph as it is right now doesn't even mention Newton's third law, which is undoubtedly crucial for lift to be generated, either.

Frankly this actually seems so clear-cut obvious that it's probable I'm missing something; if so, please point it out. Banedon (talk) 04:19, 25 March 2015 (UTC)

The excerpts quoted above are not a complete list of changes - have a look at the full versions. The controversy behind this RFC is the proposal to remove the material from the current second paragraph of that section, along with its citations. Hope this clarifies. Burninthruthesky (talk) 08:01, 25 March 2015 (UTC)

I didn't compare the entire article in the sandbox, although I did note differences in the rest of the paragraph. They don't change what I perceive though: Doug's version simply explains things better, and the difference is clear-cut enough that I don't understand the reason for the disagreement. Banedon (talk) 01:36, 27 March 2015 (UTC)

• Comment. It seems to me that different editors have effectively been commenting on two different proposals. The RfC itself proposes to replace a quantitative statement with a qualitative one (that happens to be better written). Several responses are proposing that the badly written statement be replaced with a better-written one (that happens to be qualitative). For example if the current quantitative version were expressed like this:

"The air flow changes direction as it passes the airfoil and follows a path that is curved downward. According to Newton's second law, this change in flow direction requires a downward force applied to the air by the airfoil. Then, according to Newton's third law, the air must exert an upward force on the airfoil. The overall result is that a reaction force, the lift, is generated opposite to the directional change."

would all those "replace" votes be the same?

Given that this has happened, I would suggest that the RfC issue cannot sensibly be resolved until both of the existing and proposed texts are equally well written. And given that the bad writing of the present version is the end result of a long and painful controversy about the quantitative aspect, I would suggest that the controversy needs resolving first. In other words, I'd suggest that this RfC be abandoned or closed, in order to allow the mediation process on that controversy to run its course. — Cheers, Steelpillow (Talk) 10:23, 26 March 2015 (UTC)

It looks to me like your hypothetical change would express the "current quantitative version" in completely qualitative terms. In fact, it looks word-for-word the same as the "replace" proposal. Do I understand correctly? J Doug McLean (talk) 21:34, 26 March 2015 (UTC)

Related question: all these different wordings don't use numbers, yet one is called 'quantitative' and the other 'qualitative'. Why, and what's the difference? Banedon (talk) 01:36, 27 March 2015 (UTC)

The difference is essentially whether all of the lift is said to be derived in this way. The specific remark that "downward momentum imparted to it at a rate equal to the lift" is quantitative because of the stated fact of equality. The originator of this RfC is one of a number of editors involved in a very long-running discussion over how to treat this, and this RfC is an attempt to resolve the dispute. Hence my suggested addition of the phrase, "the lift," to Doug's better-written version. Hope this helps. — Cheers, Steelpillow (Talk) 10:36, 27 March 2015 (UTC)

• Combine, in something similar to Steelpillow's proposal above. There seems to be no disagreement between in the sources that both the second and the third laws apply, they only disagree on how's best to explain - let's use both to make the explanation as clear as possible. “WarKosign” 04:01, 2 April 2015 (UTC)

Compromise statement?

Moved from Wikipedia talk:Requests for mediation/Lift (force) because I think it is more immediately relevant to this RfC. — Cheers, Steelpillow (Talk) 12:01, 7 April 2015 (UTC)

Steelpillow, When you suggested adding ", the lift," to the proposed "replace" version, I thought you were proposing a compromise you could live with. Again, the TS passage would be replaced by:

The air flow changes direction as it passes the airfoil and follows a path that is curved downward. According to Newton's second law, this change in flow direction requires a downward force applied to the air by the airfoil. Then, according to Newton's third law, the air must exert an upward force on the airfoil. The overall result is that a reaction force, the lift, is generated opposite to the directional change.

I could live with this. What do you say? (I may not be able to respond again until I return to internet access in late April.)

J Doug McLean (talk) 18:44, 5 April 2015 (UTC)

Yes I could. This really needs to go in the RfC comments not here, where others can see and comment on it. I'll move it there tomorrow if I remember. I am not convinced that it would resolve all our differences, maybe we'll have to just wait and see how things pan out. — Cheers, Steelpillow (Talk) 20:22, 5 April 2015 (UTC)

• Agree - inserting "the lift" to make it explicit that the reaction force (generated by Newton's 3rd law) is the lift improves the passage.

In other news, we're coming up on 30 days for this RFC, so if it is not closed by the end of the week I will request closure in the appropriate venue. Mr. Swordfish (talk) 15:09, 7 April 2015 (UTC)

The discussion above is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.

Status as of 1 June 2015

I see that there are some recent edits to the "Simplified physical explanations of lift on an airfoil". While I have not been participating very much in the discussion lately, I have been following it (albeit not all that closely).

I support these most recent changes. Thanks to all who have participated in arriving at consensus and hopefully we are almost ready to move on.

One suggestion (and I'm almost reluctant to make it because I don't want to drag this on any longer than necessary) is to consider restoring the following sentence:

In the case of an airplane wing, the wing exerts a downward force on the air and the air exerts an upward force on the wing.

I think providing examples along with theoretical statements helps to make the article more readable, and I don't think there's anything particularly controversial about the sentence. Thoughts? Mr. Swordfish (talk) 16:09, 1 June 2015 (UTC)

I have no problem with adding it. I think that overall there is still plenty of room for improvement, we just got stuck on one issue for far too long. IMHO, go to it. — Cheers, Steelpillow (Talk) 16:42, 1 June 2015 (UTC)