Talk:Forces on sails/Archive 1

Archive 1

Archive 2

Lift/Drag ratio and Power

The fisrt section in particular the sentence "Polar curves of lift versus drag initially look like straight lines." is a translation of french wiki fr:effort sur une voile. I have writed this sentence in french wiki. This information come from an article or a book but, i can't remember who it is.

But for me this sentence is wrong, the curve of lift versus Angle of attack are straight lines ; Polar curves of lift versus drag are for me a Parabola.

Also two solutions, the sentence "polar" is thrue, or i have done a mistake when i had read this.

best regards

Erwan1972 (talk) 16:54, 11 July 2011 (UTC)

Confusing

This article is VERY confusing and quite obviously translated from a language other than English or written by a non native speaker. As I can not even figure out the original meaning in many cases, and I do not know the subject well enough, I can not correct anything.— Preceding unsigned comment added by 164.64.39.198 (talk • contribs) 2010-07-07 20:34:34

No problem. Initial manual "clean up" translation is completed. More work needs doing, as I see the original article has since expanded. No doubt there is room for more expansion of the English version independently as well. Also the needs more proof reading, refinement . English references would be good.

Bcebul (talk) 04:17, 28 March 2011 (UTC)

Thanks for all your effort in translating this page from the French, and also to Erwan who I understand is responsible for much of the original French article.

There is much useful information here, but it still needs a bit of work to bring it up to wiki standards. One issue is that it immediately "jumps into the deep end" so that the general interest reader may not be able to follow the discussion, or may give up before reading very far. I'd like to present a simplified introduction aimed at the casual reader, and I will craft something in coming days (or weeks, depending on time).

Another issue is that it is quite long. The essence of effective writing is editing out the unnecessary stuff, and I think we need to take a sharp pencil to this article. Perhaps some subjects can be split out into their own article. I hope to find some time to address this as well.

We also need to look out for unsupported statements, and either find citations, find another way to state it, add citation needed tags, or remove them. Looking forward to working with you on this page. Mr. Swordfish (talk) 19:45, 9 August 2011 (UTC)

Today I undid some good faith edits to the introduction. I think it's important for the article to proceed from the simple to the complex and to avoid "throwing the user into the deep end" right in the beginning. There is plenty of space to elaborate later in the article.

In particular, it is possible to resolve the force vector into components of any coordinate system that one might choose. I don't think we need to allude to every possible coordinate system in the introduction. The usual choice of coordinates is to talk about lift vs drag, so we should present that first. Other approaches may be appropriate later in the article. Mr. Swordfish (talk) 15:23, 17 October 2011 (UTC)

use of energy in the article and some other issues

There are several places where energy has been used in an article about sail forces. A lot of it is simply wrong. And there is no reason using energy at all, since it's outside of the subject anyway.

For example the part talking about BETZ limit. Kinetic energy as a concept only makes sense in a well defined frame of reference, and that part mixes 2 separate references making it wrong.

In the reference of the boat, the air loses KE, but the sail does not get that energy, instead it goes to mostly turbulence and eventually into heat. The boat is sailing with a constant velocity, hence its KE is a constant. The flow of water does not get any energy either. The flow speed of water at far downstream of the boat is almost the same (just a little less than )far upsteram of the boat, hense the KE of water is the same or more accurately reduced a little and turned into mostly turbulence of water and eventually into heat.

In the reference of the water the BETZ law does not even apply, but is wrong. For a reference of that fact see article on sailing directly downwind faster than true wind in any reliable source with correct physics, including wiki in english. And using apparent wind is not correct in that frame of reference. True wind must be used instead or reference frames are mixed during the analyses, a major mistake in physics.

based on formula F = \frac12 \times \rho \times S \times C \times V^2

purpose of paragraph is : what i can improved ?

\rho

C

...

could you correct in article ?

i add note Erwan1972 (talk) 14:07, 11 April 2012 (UTC)

Some part of the article claim that:

\ C \times S represents the percentage of energy recovered over the upper(outer) surface multiplied by

the upper(outer) surface area plus the percentage of energy recovered from the lower surface multiplied by the surface area of the lower(inner) surface.

If that claim were correct no wing could have Cl above 2, or else it would recover more than 100% of the energy. Yet in reality max CL of a wing with flaps is well above that even when the reference area of the wing used to calculate CL from lift_force includes the area of the flap. That proves the unsupported and unreferenced claim to be false.

flap are not in the case of uniform flow but much more closer of Several sails: multidimensional problem resolution not yet translated.

could you correct in article, add a note ?

A note was missing ! i have translate from wp:fr sorry !

Erwan1972 (talk) 13:59, 11 April 2012 (UTC)

Treatment of aspect ratio is problemeatic. Although Cdi is dependent on AR Di is not. Instead it depends on span(b) (rig height) and apparent windspeed for a given sail force.

   Ci = {{Cz^2} \over {\pi \times \lambda \times e}} 
   \lambda = {b^2 \over S} 

Combining those 2 to get rid of lambda gives Cdi/cl = cl*S / (pi * e * b^2 ) The formula linkin lift and cl can be used to get rid of cl*S from the previous result. F_z = \frac12 \times \rho \times S \times C_z \times V^2 or Lift = cl*S * 0.5*rho * v^2, therefore cl*S = Lift / (0.5 * rho * v^2 ) Hence Cdi / Cl = Lift / (0.5 * rho * v^2 * pi * e * b^2 ) But Cdi/Cl = Di / L or Di = L * Cdi/Cl Di = Lift^2 / (0.5 * rho * v^2 * pi * e * b^2 ) And this gives the induced drag (force, not coefficient) regardless of whatever AR is. In sailing lift is limited by max rightning moment quite often, making it practical to use that formula to see induced drag doesn't depend on AR, but Cl instead does since sail area does, if AR is changed while keeping span the same. As a further reference, search for spanloading, a consept used a lot by airplane designers.

could you precise this point in article ?

i have add this in article Erwan1972 (talk) 08:26, 17 April 2012 (UTC)

As for elliptical lift distribution being an optimum for minimum indiuced drag, it's only true if span is kept the same. If heeling moment is kept the same instead, the optimum lift distribution is linear, not elliptical since it allows using greater span (rig height) for the same heeling moment and same lift force. The result (well known by aerodynamists) can be clearly seen by looking at the planforms of rigid wings on C-class cats, or the wing used on USA17 by BMW_Oracle racing durin AC33.

Yes, could you correct in article, add a note ?

remark transfered in article Erwan1972 (talk) 14:02, 11 April 2012 (UTC)

Furthermore such basic treatment of optimum distribution of lift are valid in uniform flow, that is without taking into account variation of speed and angle of airflow with altitude, ie twist of apparent wind and more wind higher up. How is total drag of the sail defined anyway, parallel to apparent wind at what height ? It can't be minimized without defining what exactly is to be minimized. If local drag close to mast head are increased by some amount while at the same time local drag close to foot of sail is decreased by the same amount, the net effect is that total sail force points more forward for a given lift. In 2D analyses it means a reduction of drag, while the local drag increased and decreased by the same amount. So minimising sum of local drag at all heights does not lead to minimum of the total drag for the sail as the elliptical as an optimum leading to minimum induceddrag assumes. That should explain why the definition is important and very relevant, yet it's not done !

87.93.222.213 (talk) 18:40, 3 April 2012 (UTC)

wiki is free, and you can correct some mistake.

In the reference of the boat, the air loses KE, but the sail does not get that energy, instead it goes to mostly turbulence and eventually into heat. The boat is sailing with a constant velocity, hence its KE is a constant. The flow of water does not get any energy either. The flow speed of water at far downstream of the boat is almost the same (just a little less than )far upsteram of the boat, hense the KE of water is the same or more accurately reduced a little and turned into mostly turbulence of water and eventually into heat.

with this sentence i can think that to keep the speed of boat i have not need of energy because i have no lost of KE !

so a rewriting is difficult, and must be done with a mitigation between : clear and correct.

a good think is to add some note for complement explaination.

be enjoy for the rewriting

best regard Erwan1972 (talk) 15:21, 5 April 2012 (UTC)

NB: some mistake could come from french translation that translator have done (me and Bcebul)

Yes, I know that wiki is free, but I beleave articles in it should be written by those using their native languages, which for me isn't english. Knowing sailing physics well just isn't enough in my opinion. On the other hand since most seems to be translations from french, I would hope someone could translate these comments in this page in french to let those french speakers see it who wrote the original article in that language for their comments. I'm hoping they would see the merits and correct their mistakes or point mine if any exist rather than begin pointless deleting & adding wars between interested parties. I can't do that since I don't speak french at all. I see no merit at all in any of the energy related analyses, but I would like to see translated comments from those who wrote it or supports it. Can you check the subject line in french to see if it's the same in french too (about a force instead of physics of sails or something like that) since a lot of this article is about matters having nothing to do with a force on sails. Wouldn't it be beter to change the subjectline rather than deleting most of the article ? — Preceding unsigned comment added by 176.93.12.223 (talk) 18:31, 6 April 2012 (UTC)

Yes too.

French article is writing at 95% by me. As i'm not god, i have done mistake.

It the reason why 5% :)

In wp:fr, sailing members have rewrinting some parts 2,3,4 times for have a quite correct texte.

When bcebul and me have translate we have see some mistake add some complement.

bcebul have mainly improve picture !

And in wp:en sailing members have rewrinting some parts too !

so each time i see a mistake or improvement i tranfers this to wp:fr or wp:en.

as i transfert improvement on wp:fr, as you are more fluent in English, no hesitation, make your correction, improvement, after i do this transfert on wp:fr.

best regard

cdt

Nb: i have add a note for "elliptical shape". But better if you have reference for C-class cats, or USA17 adds this adds this ! — Preceding unsigned comment added by Erwan1972 (talk • contribs) 13:08, 10 April 2012 (UTC)

All remarks you have show are now included in article.

best regards

Erwan1972 (talk) 08:29, 17 April 2012 (UTC)

translation of several sail

Hi,

i want to start translation of several sail (cas de plusieurs voiles), have you some remarks objections ?

best regards

Erwan1972 (talk) 10:25, 2 May 2012 (UTC)

UK or US ?

Hi, i see some revers due to this point. I discover rule of UK vs US thanks to Mr swordfish . I a created this article in a froggy UK English, and after fully correcting in a good English by Bcebul to US form. And i am not offended by this fact. Best regards Erwan1972 (talk) 09:26, 21 September 2012 (UTC)

Citations

I added a ref improve tag to this article because there are many sections that contain no citations or references at all. Granted, there are over 100 citations in the article, but that doesn't excuse the fact that many assertions are unsupported. Rather than going through the entire article and peppering it with citation needed tags, I think it's better to simply add the ref improve tag at the top of the article.

I'm actually rather concerned that some of the assertions in the article are not correct. For instance, what's currently the first sentence refers to force as a "component" of energy, and that's not even wrong - energy is a scalar quantity and does not have components like a vector does. The entire article needs a thorough going-over for verifiability.

I'm putting the tag back. Please discuss here before removing. Thanks. Mr. Swordfish (talk) 19:42, 20 October 2011 (UTC)

I couldn't agree more about the whole article needing tightening up and verifying. It seems self evident. Which is why I personally thought the tag redundant. There is already a long list of very good references which should be able to confirm the verity of the statements made in the article. Sentences which do not have a citation next to them are not necessarily unverified however. I would suggest, if in doubt, look it up in our long bibliography and reference department and add a citation or an edit. There is plenty of work to do here for those interested.Bcebul (talk) 03:20, 21 October 2011 (UTC)

hi,

for more explanation, force is linked with energy :

force is linked to dynamic pressure and Dynamic pressure is closely related to the kinetic energy of a fluid particle ; and kinetic energy ...

but i'm interest if you find any error. then i can transfert correction on french wiki.

best regards

Erwan1972 (talk) 21:10, 23 October 2011 (UTC)

Re Pression definition on Fr Wikipedia. It appears they have used the dot product of the unit vector on both sides of the pressure equation. So it is valid I think, as this gives a scalar value on both sides? But this is not as it is written in most other references including En WikipediaBcebul (talk) 21:47, 23 October 2011 (UTC)

Regarding the Zeiltheorie2.png caption: Note the decomposition is with respect to course sailed in this diagram, not with respect to wind. So drag and lift vectors are not seen here, only propulsion and side force components of net aerodynamic force. I have corrected this in the English article. I think the French article needs correcting. Bcebul (talk) 02:41, 24 October 2011 (UTC)

Yes, done on fr:wp, thanks Erwan1972 (talk) 20:40, 24 October 2011 (UTC)

p0=stagnation pressure, not static pressure, p. Bcebul (talk) 06:13, 25 October 2011 (UTC)

at infiny, as i have said that sail move and air is fixe At constant speed, consider that the sail which moves in the air at speed V0 or that the air reaches the speed V0 on the sail are exactly equivalent. '. Then we have v=0, so at infiny = static = stagnation.

i agreed with the new en:wp rewritting. On fr:wp, we haven't the terme stagnation pressure, so i done the best we can !

best regards Erwan1972 (talk) 09:27, 26 October 2011 (UTC)

User:Mr swordfish, may I suggest that, since User:Bcebul has added many references since this article was first tagged "This article needs additional citations for verification. (October 2011)," it's time to remove that comment and instead tag individual sections that you feel require have insufficient references. That would direct the attention of editors to those sections. Sincerely, User:HopsonRoad 14:05, 8 March 2015 (UTC)

lede - decompositions of net aerodynamic force

Thanks, Swordfish. Is the recent re edit ok re rotational axes? Bcebul (talk) 21:33, 18 October 2011 (UTC)

oops. Did not see your previous discussion, Swordfish. Marchaj talks about decomposition of force re boat direction in a seaway prior to discussion of wind oriented axes. If he thought it was that important, I think it is appropriate in the lede even before mentioning lift and drag. Thanks for pointing out confusion re torque.Bcebul (talk) 22:33, 18 October 2011 (UTC)

Also, the plan is to expand the Direction of force section, which precedes the lift drag section, to include forces in the course axes. So, it is logical to mention it first in the lead section.Bcebul (talk) 00:58, 19 October 2011 (UTC)

I'm not sure that 'expansion' is what this article needs at the moment. My opinion is that as it is, it's overly long and goes beyond the scope of an encyclopedic article. We should strive to simplify it and make it more accessible to a general audience. Of course, if the expansion clarifies the concepts and makes the article more understandable, I'm all for it. Mr. Swordfish (talk) 15:08, 20 October 2011 (UTC)

I concur entirely with Swordfish. I used to race 470s and ocean-going Cutlass class, but the math in this article is beyond me and drives me away from it. Kudpung กุดผึ้ง (talk) 15:43, 20 October 2011 (UTC)

That is the challenge: to make the article succinct, generally readable and still relevant to sailors on the water and in sofas as well as informative to those like me and I suspect Erwan72 who crave the physics, math and engineering. Remember, the first word in the title oozes physics, math and engineering. The English article is not nearly finished. We haven't even started on multiple sails. It may take awhile. Books have been written about this subject. I think the French version re multiple sails is a bit rough and out of reach of even more folks without tensor calculus. It doesn't have to be that way. Even Fossati, Marchaj and Larsson / Eliasson did not go that deep in their books. The article is comparatively short (but long for the unengaged). More pictures and diagrams would be good. "1000 words" and all that to engage the multitude. We could bury some more of the math in more explanation boxes for the keen.Bcebul (talk) 17:58, 20 October 2011 (UTC)

If we're going to make the article succinct and generally readable, we need to get out our sharp editor pencils and start cutting. For now, let's focus on the intro and try to incorporate the ideas of item 7 of WP:NOTTEXTBOOK.

It seems to me that the main points to be presented in the intro are:

• Air flowing past a sail generates forces all along the sail
• The forces can be combined to make a single net force
• The net force can be expressed as a sum of lift and drag
• When the boat is going downwind, the force is almost entirely drag and the wind simply pushes the boat in the direction of the wind
• When the boat is beating or reaching, air is deflected aft and the boat is propelled forwardvia newtons 3rd law / conservation of momentum
• (Perhaps a brief discussion on pressure distribution )
• Sails are used to propel a variety of vessels, not just sailboats

I don't think it's important to introduce alternate co-ordinate systems, or make statements about how it's important to understand these things or that engineers need to know it. It's also not important to introduce a lot of specialized terminology. To that end I propose the following intro:

Sails use wind energy to move sailboats, ice boats, sailboards, land sailing vehicles and windmill sails.

When air moves past a sail, Aerodynamic forces develop. These forces occur along the entire surface of the sails, but for simplicity they can be summed into one total force vector. In turn this force can be resolved into two components: lift (which is the component perpendicular to the wind direction) and drag (which is the component parallel to the wind direction).

When the sailboat is sailing directly downwind (i.e. in the same direction as the wind direction), the force is almost entirely drag force - the wind "pushes" the boat along in the direction of the wind.

When the boat is traveling across or into the wind the sails act as airfoils and propel the boat by redirecting the wind coming in from the side towards the rear. The wind moves the sail as the sail redirects the air backwards in accordance with the law of conservation of momentum.

Perhaps we could also add a brief statement that the forces are not entirely propulsive and contribute to undesirable results such as heeling, leeway, etc. Once we come to some sort of consensus on the intro, we can tackle the rest of the article. Mr. Swordfish (talk) 19:22, 20 October 2011 (UTC)

Is it possible to break this up into two seperate articles? One being math intensive for those interested in it, and the other page would be a simplified version for people/sailers to get a better idea without having to be math oriented.Beefcake6412 (talk) 19:13, 20 October 2011 (UTC)

(ec)I have not read the article in full, only skimmed through. A couple of opinions still: One, personally I like all that math, it is not usual in WP article but I would not go against it. Two, nevertheless the explanations are very long, veeeery long indeed; hiding under collapsible boxes may sound like a good idea but it is extremely bad, mostly because that's not the usual procedure (and both editors and readers need some consistency). So, if those math explanation stand, they'll better be on a linked article than hidden - Nabla (talk) 19:15, 20 October 2011 (UTC)

I think the lede should be kept very brief, mentioning the gist of the article, forces and their importance in sails, without explaining much if anything. Subsequent sections in the main body should be organised from simple but accurate introductory summaries to more in depth explanations. Bcebul (talk) 21:56, 20 October 2011 (UTC)

hi, this article is a french translation of french wiki (mainly written by me).

and on french wiki we have following rule :

"Wikipédia est à la fois une encyclopédie généraliste et une encyclopédie spécialisée. Elle est donc composée à la fois d'articles généralistes et d'articles spécialisés."

or

"Les articles très spécialisés sont ceux qui nécessitent un solide bagage préalable de la part du lecteur pour être compréhensibles. Ils ont a priori leur place sur Wikipédia. Il faut alors tenter d'en présenter une approche vulgarisée dans l'introduction."

which can be translate in english by : (Scientific) specialized article are wiki compatible, an Abstract which can be understood by any literate reader of Wikipedia without any knowledge is required.

it's the reason why we have complex formula which are translate.

best regards Erwan1972 (talk) 20:59, 23 October 2011 (UTC)

In 2011, Mr. Swordfish wrote of the article, "it's overly long and goes beyond the scope of an encyclopedic article. We should strive to simplify it and make it more accessible to a general audience." From what I see, it has only become longer and less accessible. Take, for example, the last diagram, which sets the context of forces on sails. Something like that should be at the beginning of the article, not at the end. I attempted to include a points of sail diagram that highlighted the modes of forces among luffing, lift and drag, but Bcebul suggested in an edit summary that "point of sail not directly relevant to sail force. incidence angle is. article is primarily about sails not boats." In fact, we're talking about sailing craft (land or sea) and the role that sails have for powering them. So, point of sail is the fundamental starting point, which leads to angle of incidence, mode of force (primarily lift or drag), and further to the details of how to describe lift and drag on sails as they may be configured. Clearly, four years of creating more detail has failed to create the accessibility expected of a Wikipedia article, as explained above by Erwan1972 in 2011. User:HopsonRoad 14:24, 8 March 2015 (UTC)

It is a perfectly valid argument that vessel course to wind angle could be a starting point for discussion of force analysis on sails. However, this starting point is not in any of the standard texts on sail aerodynamics I have read. Wikipedia strives not to break new ground. Generally and roughly, the approach in the textbooks is to outline the relevant basic fluid dynamics physics, then move to a discussion of equilibrium of the system based on force component analysis and steady state dynamics, introduce mathematical modelling and graphing tools especially the polar graph, then discuss factors influencing the relevant force components such as angle of attack, sail area size and shape, problems related to wind strength, sea state, point of sail, hull factors, etc. More sophisticated software modelling of the whole system is left until last. I believe the point of sail first approach may be more suited to a "how to sail" instruction article.

I see a tendency in some editors of this article to give the drag and lift components unbalanced exclusive attention when rushing to discuss sail force and boat motion. They are very important components of total aerodynamic force, but not the only ones. Arguably, in regards sail and boat efficiency, the forward drive vs resistance vs lateral force components are more relevant. Similarly an argument could be made for the laminar vs detached flow fluid mechanics discussion rather than the components which are somewhat more of a convenience than "real". The standard texts also discuss this approach, but not exclusively. Also, the article title mentions nothing about boats. Nor are sails exclusive to boats.

I am all for accessibility. Remembering that this is a subject more complex than many, it is a challenge to make a digest of a large and technical subject without letting simplification convey the sort of conceptual errors I and other editors may make. I believe in the discipline of being able to back up (though not necessarily cite) any statement with a reference. Bcebul (talk) 06:27, 9 March 2015 (UTC)

Thank you for your perspective, Bcebul. As to the order of events, by the time a student of sail design sees a text on sail aerodynamics, they already have studied the material that I propose for the build-up of this article. No-one has managed to address the issue of accessibility, to date. I propose to do so in the sand box, while preserving your hard work in providing valuable information to the advanced reader. I'm hoping that you will help in this effort, since the article's value-added is mostly your work!

Regarding the building blocks of the article, note that the article, Lift (force), has very few equations in it, yet it should be a building block of this article. Perhaps it should be built out to the extent that one sees here, but it is more accessible in introducing the topic. Regarding the scope of the article, note also that the current article uses the words, "boat" and "vessel," whereas you correctly point out that it encompasses ice and land craft, as well. So, I feel that the terms "sailing craft" and "craft" are more general. Cheers, User:HopsonRoad 13:13, 9 March 2015 (UTC)

Expert attention

I think that this article could benefit from expert attention in the area of aerodynamics (though I could not find a suitable wiki-project in that area to use in the template I added). I am a sailor with a science background, and I am sure that this article makes some mistakes when compared to, for example Lift (force). On the other hand, this article often quickly diverts into quite tricky mathematics, some of which I wouldn't know how to check or fix. It is also clear that some parts of this article were written by someone for whom English is not a first language, and, though I'm sure they've done a great job, again I feel that fixing it is beyond me.

Two examples of the kind of things that worry me are, in the section 'Role of wind' there is a lot about air 'particles' bouncing off the sails, which I know is not a good explanation of lift. In the section 'Sailing in stalled flow' the maths seems based on two pressures, but surely there is also a lowering of atmospheric pressure behind a stalled sail, even if we can ignore everything to do with stream lines and turbulence. --Nigelj (talk) 13:01, 12 August 2012 (UTC)

I'm in complete agreement with this assessment. It was over a year ago that I suggested that the article needs a thorough going-over with a sharp pencil to remove unsourced material and improve readability. It's been a year, and I haven't seen much progress. I do not think the article in it's present form is up to wiki standards and would support moving it off-line to a sandbox until it can be brought up to standard. Mr. Swordfish (talk) 14:07, 20 August 2012 (UTC)

I agree too. For a start, the introductory sentence, " Understanding the forces on sails is important for the design and operation of the sails and whatever they are moving, sailboats, ice boats, sailboards, land sailing vehicles or windmill sail rotors" is not only cumbersome, but also fails to comply with Wikipedia practice. Surely it should begin by saying what "Forces on sails" are, rather than the POV statement "understanding xxx is important...". Come to that, is "Forces on sails" the best title? Arrivisto (talk) 22:46, 31 August 2012 (UTC)

I have a bigger problem: Looking at the boat speed diagram, there is no way the boat speed should be 14kn when the boat is in irons. In irons, the boat speed is (always) 0 and the apparent wind speed is (always) the actual wind speed (14kn). This isn't abstract theory; this is basic sailing 101. I have no idea what "boat speed" (blue) in chart is supposed to mean, but it does not correspond to reality. — Preceding unsigned comment added by 66.167.140.240 (talk) 10:46, 19 August 2013 (UTC)

I presume you mean this diagram:

Apparent wind with a boat at fixed speed 7 knots red curve. Apparent wind with a boat speed fixed at half of apparent wind: wind in yellow; boat speed in blue.

Agree that it makes little sense. A boat sailing at 0 degrees to the wind (in irons) isn't going anywhere other than backwards. There is so much wrong with this article that I don't know where to even begin trying to fix it. It's now been another year and the article is still a mess. Mr. Swordfish (talk) 16:13, 19 August 2013 (UTC)

This diagram is too confusing to be useful, let's remove it. a13ean (talk) 17:05, 19 August 2013 (UTC)

Three years later, this article still needs expert attention and better sourcing. Please leave the tags in place until we reach consensus on the talk page to remove them. Mr. Swordfish (talk) 20:34, 6 March 2015 (UTC)

Yes. There seems to be a dearth of willing "experts". However, there has been for a long time an abundance of reference material for those willing to digest it and regurgitate references. Feel free to edit boldly. Consensus is the anchor of progress. In search of truth, authority should always be tested and treated with scepticism. However, in Wikipedia references trump truth. I see the article's primary purpose as describing the forces relevant to sails and sailing. Paramount is summarising conventional knowledge about their physical origin, their analysis and their relevance to sail and vessel/rotor structure and function. It is basically a physics/engineering subject. Care must be taken not to express errors in conventional terminology and concepts as a result of reaching for succinct readability. For this end see the many references. Hopefully the article will not achieve "reference clutter" in the process. The article is a bit thin on wind tunnel issues, Navier Stokes equation, The Euler equation, computational fluid dynamics, boundary layer issues, aeroelasticity modelling, structural analysis. But books have been written on these already. Would be silly to rewrite here the many tomes available on the subject. Some of the sections use illustrative examples to make a point. The references are littered with similar writing devices. Though useful, this is not a traditional encyclopedic writing structure. I like them here. Perhaps they could easily be either referenced better or the points, with references, made in a more general way?

Bcebul (talk) 07:41, 7 March 2015 (UTC)

Too much expert attention?

I jumped in with both feet in an attempt to make this article more accessible by reworking the lede. It suffers, in my opinion, from too much expertise, not too little! It reads more like a text book aimed at those who already understand fluid dynamics, rather than being the slightest bit accessible to non-technical people, who are interested in the topic. That's why I tried to build the lede from the simple to the complex. Clearly, I was too bold in doing so. I've preserved my attempt in my sandbox, if anyone wishes to review what I attempted. In summary, I would request that editors here structure the article from the simple to the technical, so that the average reader can understand at least the basics of what's being presented as suggested in the MOS for methematics. The lede should not be a string of individual sentences; indeed, the whole article is written this way. It should be a series of progressively more complex concepts in paragraph form that reflect the main text. I suggest that someone outline what the article should be in a sandbox and mine the current text, as appropriate, to rebuild it. I use this approach to good effect at Meteor, Meteoroid, Pothole, Cross-country skiing, among others. Sincerely, User:HopsonRoad 22:44, 7 March 2015 (UTC)

For a comparison of a text/equation ratio, see Lift (force). Note also that other Wikipedia articles don't have one-sentence paragraphs. I would like to see this article written with better flow. User:HopsonRoad 21:55, 8 March 2015 (UTC)

User:HopsonRoad, I don't think we have any serious disagreement here. In the interest of providing some historical context, this article started out as a (poorly) translated copy of an article from the French wikipedia. Since then, the language has been adapted but many of the citations are to publications written in French and there's a lot of info that is still unsourced. In short, I know a fair amount about aerodynamics and sailing and can follow citations to see if the cite backs up the assertion in the article, and I have to say that I am not at all confident that much of what appears in the article is correct.

Agree that the article contains a level of technical detail beyond what one would expect in an encyclopedia and that it lacks a simple introductory section comprehensible to the general reader. I would strongly support adapting this article to use the simple-to-complex narrative arc as employed in Lift (force). So I would encourage you to take a stab at re-writing the article starting with a clean slate. I've wanted to do something similar but don't really know whrere to start with this article. Mr. Swordfish (talk) 14:41, 9 March 2015 (UTC)

Introductory illustrations

The following diagrams are examples of what i feel should set the context of this article, two of them are already in the article (middle and end), the third, I proposed:

• 
  Velocity vectors boat, wind and apparent wind at different points of sail. For the same boat, apparent wind speed close hauled is much higher than downwind. Consequently close hauled speed is well over 15% of sailing downwind
• 
  Decomposition of the aerodynamic sail force to forward, and lateral components at different points of sail.
• 
  The points of sail that result in different modes of propulsion from sails: 1. Luffing (shaded red zone)—Sail flaps without generating propulsive force 2. Lift (positions B through D)—Sail generates propulsion through aerodynamic lift 3. Stalling (positions D through E—Sail generates propulsion primarily through drag.

Something like this should set the stage. The current first image is merely pretty, but doesn't illustrate the topic well, since it represents light airs. A heavy air image with multiple points of sail would be a good second image after the diagram. User:HopsonRoad 14:56, 8 March 2015 (UTC)

I propose to build a composite diagram, based on the right-hand image, that incorporates the vectors that sum to apparent wind of the left-hand image and the forces on sails vectors of the middle image. I would make it possible to see in toto and to deconstruct for different parts of the discussion. User:HopsonRoad 15:15, 9 March 2015 (UTC)

The standard literature is replete with composite force vector/wind vector/polar graph illustrations. Starting with Eiffel re his polar graph. The Marchaj texts use them. Standard stuff.

See this nice article with tidy illustrations:

http://www.finot.com/ecrits/Damien%20Lafforgue/article_voiles_english.html

Bcebul (talk) 09:29, 10 March 2015 (UTC)

Understood, Bcebul. but there's nothing suitable for this article in Wikimedia. Take a look at what I propose in the sandbox, Furthermore, I would like to have uniformity of variables in the illustrations. Right now, they are a hodgepodge. Sincerely, User:HopsonRoad 11:11, 10 March 2015 (UTC)

Re: Forces on Sail for three points of sail.jpg. It would be good to reference the size and direction of the force vectors based on calculations from a cited table, such as in Eliasson, using the formula in Relation between aerodynamic force components. Also, it looks a bit odd that the boat velocity vectors all have same value on the diagram. Bcebul (talk) 00:01, 12 March 2015 (UTC)

Referenced speed calculations done based on example polar plot from Fossati.Bcebul (talk) 21:41, 12 March 2015 (UTC)

http://www.mecaflux.com/en/sailing%20boat%20sail%20simplified%20calculation.htm Here is a web site for simple sail force calculations. Bcebul (talk) 01:55, 12 March 2015 (UTC)

I'll fix the diagram once we have nomenclature and notation decided for the variables in it. Cheers, User:HopsonRoad 00:59, 13 March 2015 (UTC)

Another questionable diagram

• 
  Plots of Lift, Drag, Lift to Drag Ratio vs Angle of Attack
• 
  For a Clark-Y airfoil the geometrical reference for angle of attack is the flat lower surface. drawing by Meggar.

The left-hand diagram has no specific provenance and it presumably intends to show C_D, but only shows D. A nicer version (perhaps from a common source) is seen here. If I were confident of the provenance and the licensing rights, I would make a nicer version. In the current article do you discuss C_L/C_D in reference to this diagram? If not, perhaps the right-hand diagram is cleaner. User:HopsonRoad 21:37, 26 March 2015 (UTC)

• 
  Boats and their spinnaker sails "running" in a regatta in Lorient, France.
• 
  Left-hand boat: Down wind with stalled airfow— predominant drag component propels the boat with little heeling moment.
• 
  Physalia physalis

Bcebul, I have questions about the above images. I would not say that the sailboats shown in the left-hand image are "running" (propelling the boat primarily with drag forces). I would say that of the left-hand boat in the middle image (first in the article). Instead, the spinnakers shown are primarily generating lift on a broad reach—the angle of attack is in line with the leading edge of the sail, not behind it. Note the significant heeling force.

As to the right-hand image, it's beautiful, but I'm not sure what it's trying to illustrate beyond the fact that man 'o war jellyfish have a "sail," whose function is not illustrated in this image. Sincerely, User:HopsonRoad 14:50, 27 March 2015 (UTC)

Use of the term "turbulent flow"

It seems to me there may be some inconsistencies in the use of the term "turbulent" with respect to the flow around the sail. I am no expert in sailing; I don't even sail. I am interested in the mechanics of it, though, and I have a degree in mechanical engineering with past experience in aerodynamics.

The technical definition of turbulent flow is when the inertial forces of the flow far outweigh the viscous forces, giving a high Renold's number (e.g. ~10^6 and above). Often in this article and others around the internet, it seems that sailors in particular use the term "turbulent flow" to describe what is correctly called "separated flow". Just because the boundary layer separates from the body (hull, sail, wing, baseball, whatever), does not mean there is necessarily turbulent flow. Indeed a turbulent boundary layer is more resistant to separation than a laminar one, a fact that is often used for advantage in reducing drag on wings, cars, and boat hulls, by "tripping" the boundary layer into turbulent flow early, in order to keep the flow attached through greater angles of attack.

So my question is, am I missing something with respect to flow on non-rigid bodies (e.g. sails as opposed to rigid wings)? Stall of a wing occurs when the flow separates, not when the flow goes turbulent. Yet in the sailing world, it seems that people prefer the term "turbulent" flow to describe separated flow. For a fluid dynamics engineer this is a confusing mix of terminology. I kind of wonder/suspect if the fact that the sail is flexible means that the flow must remain laminar to remain attached; in other words does the increased energy in the turbulent boundary layer cause the sail to distort in such a way as to lead to boundary layer separation, when on a rigid wing it would actually improve boundary layer attachment?

Thanks for any explanation / discussion on this. seenhear — Preceding unsigned comment added by Seenhear (talk • contribs) 20:21, 3 April 2015 (UTC)

You make a good point, seenhear. See "Flow separation" versus "Turbulence." What you're perhaps hearing from sailors is imprecise conflation of the two concepts. We can clean this up in the article. Cheers, User:HopsonRoad 20:59, 3 April 2015 (UTC)

...Edited to add my username and sig. Seenhear (talk) 18:57, 6 April 2015 (UTC)

Reorganization?

I would like to propose re-organizing this article in a manner that progresses from general to specific, while preserving the hard work that User:Bcebul has done. I would envision first shaping the outline, then bringing content across. I like the feature that occurs in two places where distracting detail remains hidden until the interested reader uncovers it. I recommend using that feature a bit more. Please look at (and edit) the Sandbox and place your comments, below.

I have drafted a lede and an overview for the review and editing of others. User:HopsonRoad 13:33, 16 March 2015 (UTC)

Guidance on making technical articles understandable

Here is some good guidance: Wikipedia:Make technical articles understandable. User:HopsonRoad 12:06, 28 March 2015 (UTC)

Let's discuss how to frame this article, in light of the guidance given.

• Audience: I suggest that this article should be accessible to anyone, who can master a sailing craft on any point of sail. This would correspond to: "The knowledgeable reader has an education in the topic's field but wants to learn about the topic itself."
• Technical content: Let's not assume that the reader is familiar with fluid dynamics, but put that level of discussion at the end of introductory material in a given section and towards the end of the article, as a whole. "Increasing the understandability of technical content is intended to be an improvement to the article for the benefit of the less knowledgeable readers, but this should be done without reducing the value to readers with more technical background."
• Lead section: The lead should reflect the content, logic and flow of the article. "...the lead should provide an understandable overview of the article. While the lead is intended to mention all key aspects of the topic in some way, accessibility can be improved by only summarizing in the lead, and including the technical details in the body of the article."
• Put the most understandable parts of the article up front: The most understandable parts are points of sail, which generate apparent wind velocities. The second most understandable parts are force components on sails, followed by the reactive forces that make those forces possible.
• Write one level down: It's reasonable to assume that a sailor has the equivalent of a baccalaureate, so having much of the article understandable by someone graduating from high school would qualify.
• Add a concrete example: Pictorial illustrations of actual sailing craft, tied to the principles discussed are important here.
• Explain formulae in English: This is key to understanding, especially if a force or coefficient is proportionate to the square of velocity.
• Add a picture: We have this covered!
• Don't oversimplify: No danger here!

My thoughts. Yours? User:HopsonRoad 21:13, 28 March 2015 (UTC)

Comments on sandbox

Please make your comments, here:

Lift and drag are not "modes of propulsion". They are components of total aerodynamic force. That is all. The forward driving component "propels" the boat. On many angles of attack where some attached flow occurs, the lift component contributes to the forward component. However, even with running, there is a lift component perpendicular to the apparent wind on sail contributing almost nothing to the forward component. On broad reaching, drag, parallel to wind, also contributes to the forward component or " propulsion".Bcebul (talk) 02:32, 17 March 2015 (UTC)

Thank you, Bcebul. I have fixed this in the lede and elsewhere. User:HopsonRoad 11:25, 17 March 2015 (UTC)

Take care with the term power. It has a very specific meaning in physics. The article should stick with that narrow context to avoid confusion.Bcebul (talk) 07:53, 17 March 2015 (UTC)

I'm comfortable with its use, here in the lede, [User:Bcebul|Bcebul]]. It bridges between the common understanding of power, appropriate to an encyclopedic introduction and the discussion of force, used in the body. Additionally, there is no broken link in logic, since power is force times distance per unit of time. The force is as discussed in the body; distance and time just fall out with the motion of the vehicle. User:HopsonRoad 11:31, 17 March 2015 (UTC)

Discussing the definition of sail vs wing is a bit beyond the scope of this article. Try sail or wing for that. Birds use wings for propulsion. Not relevant here. Bcebul (talk) 08:12, 17 March 2015 (UTC)

I've been very explicit to link to Lift (force) and graphically depict the airfoil as an object providing lift, as opposed to a wing, which may constitute many different structures. I differentiated sails from wings in the lede. User:HopsonRoad 11:25, 17 March 2015 (UTC)

Whether the turbo fan is moved by natural wind or a jet fueled engine makes no difference to the basic fluid mechanics, or force component descriptions. Not much point in arguing too much the differences here. For brevity,the article is about sails only. Things like Turbosail can have their own article.Bcebul (talk) 08:12, 17 March 2015 (UTC)

I disagree on this point, Bcebul, it's relevant to note that sails are adjusted to a natural force, i.e. the wind, whereas those other airfoils are not. In the body, I have changed the awkward language there. it's appropriate to point to airfoils attached to sailing craft on the fringes of the topic, A turbosail could be mentioned in passing, whereas a kite sail is just out of bounds, in my opinion. A windsurfing sail is an important object lesson because, instead of heeling away from the wind, it is brought windward to provide an upward component of lift that reduces hull drag. User:HopsonRoad 11:25, 17 March 2015 (UTC)

Hi there. I was asked to contribute. While I don't have my copy of Marchaj handy, if we're going to rewrite, that should be a primary reference for the maths. From some random website: "Sail Performance, based on C. A. Marchaj's classic Sailing Theory & Practice, has established itself as the standard work on the subject and is now acclaimed as a milestone in sailing literature." I support the idea of "Re-organizing this article in a manner that progresses from general to specific", not only because it makes more sense, but because most people can't read the formulae. However, using this criteria for evaluation the current sandbox is not a significant improvement, and is even perhaps the opposite. I would encourage going so far as to limit any algebra or formulae to a closing section, 'Formulae and calculation' which exclusively approaches the mathematics. All other sections within the article should be general and could have 'see also' links to the latter section. prat (talk) 00:55, 24 March 2015 (UTC)

Thank you for your observations, prat. Currently, I don't see the article and the sandbox converging toward "re-organizing this article in a manner that progresses from general to specific" while limiting algebra and formulae to a closing section. Would you consider being bold and doing the necessary work, either in the article or the sandbox to achieve what you suggest? Sincerely, User:HopsonRoad 12:41, 24 March 2015 (UTC)

On further consideration, prat, your standard of no formulae until the end may be too strict. See, for example, Quantum electrodynamics—a WP:Good Article in Wikipedia:WikiProject Physics, where the first formula comes about ⅓ of the way into the article and some serious mathematics occurs about half way in. I would be happy, if the non-technical person got the idea by a third of the way in, and the more capable reader could go deeper upon further reading. User:HopsonRoad 21:10, 24 March 2015 (UTC)

Notation

Suggest use V_subcript for velocity vectors. S _subcript for speed components of velocity. e.g. V_TW true wind velocity S_TW true wind speed Bcebul (talk) 01:38, 11 March 2015 (UTC)

Thanks, Bcebul. How do we address the notation in Force components with respect to wind section? Those are scalars, so you're suggesting that the corresponding vector for S_TW in the textual equations would be V_TW in a diagram. Right? I concur with the mathematical rigor, but wonder whether it's more understandable to the lay reader. I'm thinking that, as long as the diagram shows a vector, S can denote its scalar value. User:HopsonRoad 01:58, 11 March 2015 (UTC)

The reason for care here is that vector addition is not the same as scalar addition.

$\mathbf {V} _{TW}$ +$(-{\mathbf {V} _{boat}})$ $\neq V_{TW}+(-V_{boat})$.

I guess it would be acceptable to the math cognoscenti to use the boldface convention for vectors and plainface for scalars keeping same lettering. The mathematics challenged may miss the subtlety. The vector above script convention is favoured by the Europeans.

${\vec {V}}_{TW}$ +$(-{{\vec {V}}_{boat}})$ $\neq V_{TW}+(-V_{boat})$.

If we are clear to the readers in the variable definitions, you are correct I am wrong. Best to stick with the same lettering.

see: Help:Displaying_a_formula

https://en.wikipedia.org/wiki/Help:Displaying_a_formula

and :

https://en.wikibooks.org/wiki/LaTeX/Mathematics

Bcebul (talk) 05:04, 11 March 2015 (UTC)

I understand and concur with what you are saying about clarity of notation to distinguish vectors from scalars. My concern was choosing a convention that bridged between textual formulas and diagrams. It's more difficult and graphically fussier to use the vector above convention in a diagram. So, I would favor the boldface convention for ease of rendering and accessibility's sake.

OK. Bcebul (talk) 00:01, 12 March 2015 (UTC)

Also, in the table guide to the aerodynamic and hydronamic forces on the boat, the call-outs are bold face as are the explanations, but only some of them are vectors. What's a good way to address this? User:HopsonRoad 16:11, 11 March 2015 (UTC)

I can fix that in the diagram. Bcebul (talk) 00:01, 12 March 2015 (UTC)

That's great, Bcebul. I recommend that, when you do so, you are satisfied that the notation is what should become standard throughout the article. (See below under Nomenclature.) Also, could you give those illustrations an opaque background, please. User:HopsonRoad 02:21, 12 March 2015 (UTC)

Nomenclature

I'm trying to gather all the different ways of expressing the same variable in the article and present them here, so we can agree on one term. For example, in one place apparent wind velocity is V, in another it's V_A, and in another it's V_AWe (this latter one is a scalar). Watch this space for items to resolve. User:HopsonRoad 02:11, 12 March 2015 (UTC)

Still working on that. But I think some of these are actually different variables. The last is "apparent effective wind speed" used for the force calculation adjustment for heeling situations.

In the force equations derived from Bernoulli, V is the airflow velocity relative to the sail, i.e. apparent wind. Relativity is often a trap for newcomers. In the context of general aerodynamics, simulations and wind tunnels, true wind is not even considered, so it is just V. Only on the water is true wind relevant. Then it needs to be converted to apparent wind for any relevance to sail force.Bcebul (talk) 03:51, 12 March 2015 (UTC)

Hi Bcebul. You might wish to look over the list of variables that I compiled in a special section in the sandbox. In some cases the notation itself varies, in other cases the nomenclature for the same variable varies. I suggest that you look over variables with conflicts and put your recommendation to the right, e.g. Recommendation: True wind angle: $\beta _{TW}$.

There's more to tackle, but that list addresses the core of the article until the section on Wind and sail interactions.User:HopsonRoad 00:09, 13 March 2015 (UTC)

Bcebul, I note that in the section, Relation between aerodynamic force components, the notation for apparent wind changes from α to β and α becomes angle of attack on sail. I don't see a standard for notating those terms, but I feel that they should be uniform within the article. What do you suggest?

Also, it's unclear what the diagram, File:boataeropolar.svg, is trying to explain in all its detail. I note only one sail, yet it has a different apparent wind than that of the boat. That would be expected, if there were a jib providing a slot effect, but there's no jib here and it appears to complicate whatever this diagram illustrates. User:HopsonRoad 21:30, 20 March 2015 (UTC)

Thanks, HopsonRoad, for pointing that out. There is indeed only one apparent wind velocity. Fixed. The apparent wind angle is only the same as the angle of incidence of the sail if the sheeting angle (or trim angle) is zero. Still working on consistency of labels as time permits. The lift drag curve for angle of attack diagram is an example very common in the Marchaj and Fossati texts to demonstrate optimal angles of incidence. Another way is to superimpose boat lift vs drag curves with sail lift drag curves such as in Kimball pg 61 figure 3.15.

"...3.4 Why Is Sailing Upwind So Complicated? Is it really necessary to draw so many diagrams and write so many formulas to describe sailing? Sadly, I have been unable to find a shortcut path to the speed diagram. In fact, sailing is really more complicated than all the diagrams and formulas suggest..." Kimball pg 73

Bcebul (talk) 06:17, 23 March 2015 (UTC)

Thanks for getting back, Bcebul. Does this tell the story, correctly to a degree appropriate for an encyclopedia readership?

Polar diagrams, showing lift (L), drag (D), total aerodynamic force (F_T), forward driving force (F_R), and lateral force (F_LAT) for different points of sail

(V_A is constant in these examples, which means that either V_T or V_B varies.)

• 
  Close-hauled: Note that the lateral force is highest and driving force is lowest close to the wind.
• 
  Reach: Note slight change in angle of attack (alpha), increase in driving force and decrease in lateral force.
• 
  Broad Reach: Note that with apparent wind behind the sail, the sail has stalled and lift has diminished.

These are adapted from Pp. 61-63 Garrett, Ross (January 1, 1996). The Symmetry of Sailing: The Physics of Sailing for Yachtsmen. Sheridan House, Inc. p. 268. Cheers, User:HopsonRoad 14:27, 23 March 2015 (UTC)

Parenthetical referencing

Bcebul. to preserve your references with page numbers I propose to use parenthetical referencing, which will also streamline the reference list. See, for example, how in-line notes link to citations, here. User:HopsonRoad 00:42, 13 March 2015 (UTC)

sounds fun Bcebul (talk) 00:52, 13 March 2015 (UTC)

Text ready to bring across?

Bcebul, I'm wondering if you would be amenable to bringing the following two items across from the sandbox: the lede and the Overview? Elsewhere, we appear to have taken divergent paths: in the sandbox I've proceeded from the general picture of sailing craft subject to wind towards the action of airstream on sails. In the, article as it stands, the approach appears to be building out from the specific (airstream on sails) to the general. It would be desirable, if other editors could guide us on which model is preferable. Sincerely, User:HopsonRoad 17:30, 25 March 2015 (UTC)

Thanks User:HopsonRoad. Your good work has been an inspiration. I like your diagrams and have put some more into the article. I have acted on your advice on restructuring the opening. Tightening the nomenclature has been useful for clarity (still some more to do). As for the general approach, as I have already said, the subject is forces. Though sail forces on a sailing craft are dependent on the craft their other relevant forces and their operation, and the balance of forces is very important, the operation of craft is not the prime subject. So, I have a problem with your sandbox lede. It seems to be the opening to another article and not directly to the point. I think listing the nomenclature in tables the sand box was useful. However, I think introducing consistent definitions as needed in the main article is more brief and less cluttered. Bcebul (talk) 22:00, 25 March 2015 (UTC)

I very much appreciate your thoughtful reply, Bcebul. I understand your desire to keep focus on what happens to the sail. The lede and introduction that I proposed in the sandbox are based on the premise (which is the key point of your fine illustration) that forces on sails are very much dependent on the reactive forces from the sailing craft. I felt that it was important to illustrate the scope of those reactive forces using ice boats in contrast to sailboats, which then leads to the topic of sail configuration to provide the power required by the craft to overcome forward resistance forces. I think that could we could discuss that relationship between applied and reactive forces here to agree on a scope for this article. Then we could work on the lede and introduction. There might also be a companion article on "Forces on sailboat hulls." Cheers, User:HopsonRoad 15:59, 26 March 2015 (UTC)

A quick comment or two: I find the structure of the proposed new article much better than the old one (where, as it seems, editors added chapters in random order, which now makes it difficult to understand the connections between the sections). It is also less technical and easier to understand. Of course, the information in the existing article shouldn't be lost, if possible. Is it intended to merge some sections still? Or transform them into their own articles? --PaterMcFly talk ^contribs 12:27, 2 August 2015 (UTC)

Thank you for your comments, PaterMcFly. I propose that, when the new material is brought across, the entirety of the current version be preserved in the sandbox for future mining. Unfortunately, much of the material presented appears to represent original research, which may be true, but is inadequately referenced. The material that is adequately referenced will be brought across, hopefully with clearer writing than currently exists. Sincerely, User:HopsonRoad 02:31, 3 August 2015 (UTC)

Yea, that might be a problem. Most of the diagrams with their explanation can be sourced though. I have a 2012 german book here that reproduces many of the diagrams in this article almost 1:1, giving their original sources. So when the source for some statement is unclear, that might help. --PaterMcFly talk ^contribs 20:37, 3 August 2015 (UTC)

Per the discussion above and at Wikipedia:Peer review/Forces on sails/archive1, I propose to bring across the content at Talk:Forces on sails/sandbox and place the current article content in that sandbox. I feel that the substitute text works better than the current article. A lot of cleanup is still required with the references. Please offer concurrence or not on the move. Absent a consensus against doing so, I would make the move on Friday. Sincerely, User:HopsonRoad 00:49, 5 August 2015 (UTC)

I have brought the developmental material across and exchanged it with the pre-existing legacy material. User:HopsonRoad 13:49, 7 August 2015 (UTC)

Planform

The term "planform" is being used in this article to describe the outline shape of a sail. Is this normal usage or has it been mistakenly borrowed from books about aeroplane wings? — Cheers, Steelpillow (Talk) 12:53, 20 September 2015 (UTC)

Thank you for checking in, Steelpillow. Here is a sampling of citations that use the terminology in reference to sails:

• Minimum Induced Drag of Sail Rigs and Hydrofoils Part 1: Planar Planforms
• Planform efficiency and effective aspect ratio
• Planform Sailwing Design using Symmetric Cross Sections
• The Aero- and Hydromechanics of Keel Yachts by J.W. Slooff p. 301

Did you have some other term in mind? Sincerely, User:HopsonRoad 19:13, 21 September 2015 (UTC)

Hi, in aircraft design, use of the term "planform" originated to describe the main wing and perhaps the whole machine, it is not used for vertical surfaces such as the tail fin. When I saw it being used on Wikipedia to describe sails, keels and similar vertical surfaces, I wondered whether this variant usage was standard or whether Wkipedia editors had mistakenly borrowed and misapplied the terminology of specifically aircraft wing aerodynamics. Your example sources show that it is indeed standard and there is no mistake. Thank you for clearing this up for me. — Cheers, Steelpillow (Talk) 19:24, 21 September 2015 (UTC)

Thanks for your interest and your reply, Steelpillow. The term is applicable to all lifting devices. An aircraft tail fin provides such lift as it contributes to directional stability and even more significantly, when used to offset adverse yaw. The confusing part of the word is "plan...", which implies that we're looking at the outline of a shape in the horizontal plane! Cheers, User:HopsonRoad 00:55, 22 September 2015 (UTC)

Legacy material

The previous version of this article is preserved here for those, who may wish to draw on it for further development. User:HopsonRoad 14:33, 25 September 2015 (UTC)

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