Talk:Dihedral (aeronautics)

High mount of wings itself does not increase the roll stability
Imagine a plane with high mounted horizontal wings (with no dihedral). This plane flies straight, with no roll. Weight force is hooked at the mass centre and directed vertically down, lift is hooked above the centre and directed vertically up.

Now some random cause rolled the plane, for example, 5 degrees left. If high mounted wings are expected to recover the plane to horizontal position i.e. make a rotation of plane, they MUST apply some torque on it. But what really happens here: weight is still hooked at the centre, thus it doesn't cause any torque (the arm is zero). Lift is hooked at some point which is nearly above the centre, but deviated by 5 degrees left. And lift is directed not vertically up, but 5 degrees left, and actually its direction is exactly the same as the direction of the arm (i.e. vector from the mass centre to hook of lift force). In other words, vector of lift force is parallel to vector of arm, and thus lift doesn't generate any torque, either. Thus, there is still no torque and the plane does not recover!

It's better understandable if drawing is seen, but I don't know how to attach a drawing in the discussion pages.

In fact, if a random left roll occurs, it causes a left sideslip, and the fuselage begins to create a lift force directed to the right. And this lift can generate a torque. The hook of this side lift is usually around the centre of fuselage, and thus lower than the mass centre of the whole plane (mass of the wings raises the mass centre). And thus, it generates a torque which makes even more left roll and worsens the situation!

It's true, however, that high mounted wings increase pitch stability.

--Grzes 23:49, 26 Jan 2005 (UTC)


 * While I follow your argument, this clearly isn't the case. I haven't done any mathematical analyses, but I have built a couple of simple chuck gliders! It's easy to demonstrate that where there is a lump of mass hanging below the wing the aircraft will fly a lot more stably than if the same mass is added above the wing, all else being equal (and with no dihedral to cloud the picture). In fact the aircraft was so unstable with the mass above it tended to flip over and fly the other way up! This is an example of how aerodynamicists sometimes seem to fall into the trap of not actually looking at things with their own eyes, but to bury themselves in equations. Notably, the infamous assertion that "the bumblebee cannot fly". Yes it can, open your eyes! Therefore the analysis MUST be wrong... Graham 22:47, 27 Jan 2005 (UTC)


 * How, Graham, can you be sure that the instability is not due to pitch instability as suggested by Grzes? If his analysis is logical, and you claim that he is wrong, where is the discrepancy in his logic? I am a beginner to flight mechanics and I am finding these pages quite confusing.


 * I don't think the 'analysis' above is logical. It is wrong, though it's hard to be sure since the terms used (e.g. 'hooked at the centre') are not the conventional scientific terms and so my interpretation of what the writer meant might be wrong. If you are learning flight mechanics then I strongly recommend that you don't use Wikipedia as a text book! I believe that the explanation in the article is correct, but I wouldn't stake my degree on it. Incidentally, the statement about a high-mounted wing conferring pitch stability is possibly even more confusing - it's much less obvious to see how that might be the case than with roll - but in any case the 'pendulum effect' will confer stability in all axes where gravity acts normal to the axis, which would be roll and pitch. If you accept that stability is conferred in the pitch axis by the effect, why would you discount it in the (much more obvious) roll axis? What's the difference, from the point of view of gravity acting? Having read through Grzes entry again, just to check, I'm pretty sure he's simply wrong - the centre of mass will be offset horizontally relative to the centre of lift, and this sets up a torque which acts to restore the original position. The sideslip drag (not lift) that the low fuselage position might create is a possible factor, and it would act to further destabilise the position, but its effect must be absolutely tiny, and the pendulum effect easily overcomes it. Finally, remember that the talk pages are not the article. Often things get debated and clarified on the talk pages at great length, especially where some misunderstanding exists. It doesn't mean that the misunderstanding should cast any doubt on what the article itself actually states. Personally I'm happy to take the time to try and clarify people's misunderstandings as far as I am able to do so, but entering into these discussions in itself shouldn't be taken as a sign that the original point is especially worthy. If someone said that roll stability was conferred by the action of invisible fairies pushing on the low wing, then such a view could be easily and quickly put right - but it doesn't mean that that the original idea was worth anything, just because it exists in print on the talk page. Graham 23:29, 19 December 2005 (UTC)


 * Actually, high mounted wings do increase stability, but not because of the fact that they are above the center of gravity. When an airplane with high mounted wings is in sideslip, the root edge of the wing facing into the wind will experience a local increase in angle of attack (because the air is flowing around the top of the fuselage), and the root of the wing on the downwind side will experience a local decrease in angle of attack (again, since the local air is going over the top of the fuselage). This creates a restoring roll moment, creating stability. Similarly, a low wing will have decreased stability, since when it is in sideslip, the root of the upwind wing will experience a local decrease in angle of attack (since the local air is going around the bottom of the fuselage), while the root of the downwind wing will experience a local increase in angle of attack (again, since the air is flowing around the bottom of the fuselage in that region). With regards to the claim that "aerodymaicists must be wrong", the aerodynamicists aren't saying that there's no stability contribution to high wings (nor, in fact, are they saying bumblebees can't fly - that's based on a common misconception, and a fundamental error in analysis of low Reynolds number flows, but I digress...).  - Signed, a lowly Aerospace engineering masters student  —Preceding unsigned comment added by 128.138.6.58 (talk) 05:05, 4 November 2010 (UTC)
 * Minor flow field effects are hard to establish and are not easily separable from other effects. Your effect (high wing + body interference "increases stability" (i.e. creates dihedral effect)) may indeed be an actual effect, but you are incorrect to suggest that vertical CG (moving downward) doesn't also do this, although you may not have intended to make that suggestion.  Since a moment must be defined as about a point, the redefining of that point will change the moment directly and linearly.  That "point" is the CG and moving the CG redefines the point and so the vertical CG has a direct and linear effect on dihedral effect.
 * Your effect is one of those "everything in the flow effects everything else in the flow" kind of things. Measurement of it depends on holding everything else constant, which I assert is really pretty hard to do - heck, you're changing the whole shape of the thing.  You'd also have to describe the nature of the fuselage.  If it was porous like in a ultralight, your effect doesn't apply, while "vertical CG" always applies.  In your scenario, the vertical CG compared to the wing necessarily changes at the same time as going from low to high wing.  It's hard to separate that effect from so many other effects from so many other flow field changes.  There would be a lot of "destructive digression" involved in explaining how every bump changes "stability" (i.e. dihedral effect) via its effect on the flow field.  That would only serve to confuse and most of it would be off topic - more suited to a discussion on flow fields.
 * 108.7.171.30 (talk) 06:25, 11 October 2011 (UTC)

Center of lift vs. center of gravity
I have read several explanations of how dihedral produced roll stability and this is the first time I've heard anything about this sideslip theory. The theory has merit and may be part of the picture but is not the generally-accepted theory. If this is a personal theory and not an established one it should not be put forth as the actual explanation. I think this requires some discussion and possibly changing the article.

The mistake most people make is assuming that movement around the roll axis somehow affects how much lift a wing produces. It doesn't; it can't. In the absence of gravity an aircraft will fly the same way no matter what roll angle it is at. The other thing people don't take into account is that, like any other force that is spread over an area, all of the lift produced by the entire airframe acts as if it were concentrated at a single point--the center of lift.

If the center of lift is above the center of gravity the aircraft will act as if it were hanging from a string. If the aircraft rolls, barring any other external forces, it will swing like a pendulum back to the position where the center of lift is directly over the center of gravity. If the center of lift is below the center of gravity the aircraft will act is if it were siting on a pin, clearly an unstable position. This is why a high-wing aircraft, like a Cessna 172, has very little dihedral. It doesn't need it. The center of lift is above the center of gravity by virtue of having the whole wing above the center of gravity. A low-wing aircraft, unless it is designed for maneuverability (i.e. aerobatics or dog fighting), will usually have more dihedral than a high-wing aircraft. The extra dihedral is required to raise the center of lift. This is why a high-wing aircraft is inherently more stable than a low wing aircraft. Rsduhamel 17:38, 22 Mar 2005 (UTC)


 * Two points. The pendulum effect is definitely very real - that is, I think, what my earlier comments (and actual experiment) were meant to demonstrate. The whole torque-couple argument stated at the top of this page is erroneous (there is a torque-couple formed because the centre of gravity is offset to one side by the roll). The second point is that the sideslip theory seems to be the now commonly accepted one by all serious works on the topic. By serious works I mean books such as A.C Kermode's "Mechanics of Flight", and PPL training manuals, etc. Many other laymans' guides still get it wrong. Roll by itself cannot change the amount of lift, as you correctly state - so any argument that is based on this idea is wrong by definition. However, a sideslip CAN create additional lift, since a small lateral airspeed results which sees the dihedral as an angle of attack. Your argument about raising the centre of lift makes sense, but I believe it is not really the purpose of dihedral. Many low-wing aircraft do not have sufficient dihedral to place the centre of lift above the centre of gravity - to do this would require a very extreme amount of dihedral which you just do not see in practice. The sideslip theory explains the roll stability much more elegantly since it only requires a small dihedral angle, as seen in practice.


 * To add to my point, I'll quote from 'Mechanics of Flight". If you have an interest in aerodynamics but don't need screeds of equations, this book is a highly readable introduction, and very well respected. Recommended.


 * "Mechanics of Flight", 10th edition quotes from page 280+: First it dismisses the erroneous "horizontal aspect" explanation in a couple of paras. "What then, is the real explanation as to why dihedral angle is an aid to lateral stability? When the wings are both equally inclined [straight and level] the resultant lift on the wings is vertically upwards and will exactly balance the weight. If, however, one wing becomes lower than the other, then the resultant lift force will be inclined to the vertical, while the weight will of course remain vertical. Therefore the two forces will not balance and there will be a small resultant force acting in a sideways and downwards direction. This force is temporarily unbalanced and therefore the aeroplane will move in the direction of this force - i.e. it will sideslip - and this will cause a flow of air in the opposite direction to the slip. This has the effect of increasing the angle of attack of the lower plane and decreasing that of the upper plane. The lower plane will therefore produce more lift and a restoring moment will result." It goes on to discuss the variation of the centre of pressure ALONG the wing in this case. Following this there is a further section titled "High wing and low centre of gravity": "If the wings are placed in a high position and the centre of gravity correspondingly low, the lateral stibility can be enhanced." Curiously, it explains this in terms of a lateral drag force arising from the sideslip forming a couple with the centre of gravity acting to right the plane. This seems novel, but in fact it's much what you're saying, since this drag force appears as a slight skewing of the lift force. The book then goes on to dicuss other factors affecting lateral stability - sweepback, fin area, etc. etc.


 * I hope this isn't labouring the point too much, but I also took a look at "The Air Pilot's Manual" by Trevor Thom, Volume 4, page 69. This book is the standard training manual for the PPL in the UK. It too puts forward the sideslip theory for dihedral. "As the aircraft sideslips, the lower wing, due to its dihedral, will meet the upcoming relative airflow at a greater angle of attack and will produce increased lift. [...] The rolling moment so produced will tend to return the aircraft to its original wings-level position".


 * While these references are not the last word on aerodynamics, they are both well-respected. I hope it corrects your impression that the sideslip theory "is not the generally-accepted theory". As far as I can tell it is the generally accepted theory.Graham 01:18, 23 Mar 2005 (UTC)

Erroneous explanation of stability
Guys, I'm adding the cleanup tag because the explanation of the stability effect in this article is simply wrong. It's not about the amount of aerodynamic force, it's the direction that matters. When an aircraft with dihedral rolls, the wing that's closer to horizontal will generate the same lift as the other wing, but the lift vector is closer to vertical, opposing gravity more directly than that of the other wing. It's not related to the angle of attack, or any sideslip. The stabilizing effect is there as soon as the wingtips aren't at the same height relative to the horizon. I'll come up with some corrected diagrams and fix the text as well.


 * Sorry, but you are simply wrong. Any authoritive book on the subject will use the sideslip/AoA explanation, and be at great pains to point out that the explanation you're proposing is incorrect. Dihedral in itself doesn't change the lift vector angle from being exactly vertical. Also, you have not signed your comment. I will remove the cleanup tag - feel free to discuss this further if you wish, but please refer to a decent textbook on the topic before making yourself look foolish. (One I recommend is "Mechanics of Flight" by A.C. Kermode, which is a very accessible and well respected textbook on the topic). Graham 11:29, 12 April 2006 (UTC)


 * The difference in angle of attack due to sideslip causes a rolling moment which tends to roll the body to point the lift vector so as to oppose the sideslip. The fundamental purpose of dihedral is the cancellation of sideslip. It is therefore nonsense to claim that sideslip has no effect. Dihedral does not control the inertial roll angle, but tends to keep the plane of incidence in the plane of symmetry of the aircraft,  Much of the above discussion confuses inertial roll with aerodynamic roll. In analysing the stability of aircraft, the reference point is taken as the centre of gravity, so that all gravitational moments are identically zero. Shifting the cg changes all the values of stability derivatives used in the analysis.  With stick fixed the lateral modes consist of roll subsidence, Dutch roll and spiral instability, and dihedral is important for the latter two. I suggest reading Arthur Babister's  Aircraft Dynamic Stability and Response. Elsever 1980, ISBN 0080247687. Gordon Vigurs 19:50, 27 June 2006 (UTC)

The problem with dihedral is, it has more than one effect. Sideslip results in side force, yaw and roll torques due to dihedral. The side force effect is of second order, but dihedral tends to roll the aircraft to cancel sideslip, and is significant in stabilising the spiral mode, but has a de-stabilising effect on the Dutch roll. It is usually difficult to make both stable. High wing aircraft generate a dihedral effect because the body modifies the local angle of attack, and this effect is modified by sideslip. There is a further dihedral effect arising from wing sweep, to the extent that anhedral is required for a stable Dutch roll on highly swept fighter configurations.Gordon Vigurs 09:39, 7 August 2006 (UTC)

Etymology of Cathedral
I removed the sentence about "cathedral" having the same derivation as "dihedral". Cathedral comes from the Latin word Cathedra for "chair", referring to the chair in which the bishop sits when presiding over the liturgy in his cathedral. The derivation has nothing to do with the structure of the ceiling. See Cathedral and Catholic Encyclopedia: CathedralSbreheny (talk) 04:42, 7 August 2008 (UTC)

WikiProject class rating
This article was automatically assessed because at least one WikiProject had rated the article as start, and the rating on other projects was brought up to start class. BetacommandBot 09:48, 10 November 2007 (UTC)

Muddled! :-)
This article muddles an important difference between Dihedral Angle and Dihedral Effect.


 * References to fixed-wing aircraft geometry should always refer to Dihedral Angle.
 * References to aircraft stability should always refer to Dihedral Effect.


 * Dihedral Angle is the angle the wings meet (of course).
 * Dihedral Effect is a rolling moment produced in proportion to sideslip angle.

Dihedral Effect is called "Dihedral Effect" because increasing Dihedral Angle increases the rolling moment produced by sideslip.

BUT! A gazillion other things also change the rolling moment created by sideslip. Such as: Wing sweep, Vertical CG, height of sideforce-producing  surfaces like fins, fuselages, etc., etc.

Such things should be made clear in the article. I will set out to do that.

-- Gummer85 (talk) 03:57, 3 April 2009 (UTC)

Not the place for Lateral-Directional Stability
This article (but mostly the discussion) digresses too much toward Lateral-Directional Stability. Dihedral Effect is a subset of Lateral-Directional Stability.

Perhaps a new article could be created for "Lateral-Directional Stability" if we really want to include the whole miasma. That would be the proper place where everyone could post all their MAD THEORIES! :-)

The article "Dihedral" should be kept and renamed "Dihedral (flight)" or something like that. It should be small with a few pretty pictures of dihedral and anhedral like it already has. It should have the distinction between angle and effect of course and the fact that effect is important for Lateral-Directional Stability which it refers to and be done with it! :-)

--Gummer85 (talk) 06:03, 3 April 2009 (UTC)
 * << I've changed my mind on including a little L-D stability by discussing DE effect on Spiral Mode. It's a little redundant w/ Spiral Mode, but material to the main subject.  And, now that it's discussion is correct, it doesn't scream "delete me!" to experts.  It's okay to keep now in my new (but not humble :-)) opinion. Gummer85 (talk) 16:40, 20 May 2009 (UTC)>>


 * Don't forget to cite your additions and changes from relialble souces. The article has none, so if you are able to cite some of the other items at the same time, that would be very helpful. - BillCJ (talk) 08:21, 3 April 2009 (UTC)

Yeah. I hear ya. I am usually moved powerfully to "make it correct" first. It's more immediate, if not more important. Actually, correctness is more important than citing, but not by as much as it is more immediate. The kind of material I am fixing here is "common knowledge" among experts in the field and any error should be corrected quickly enough by other experts. Although, given that glaring "confer Longitudinal static stability to roll axis" error that sat for so long, I'm not so sure of this any more. :-).

Because it is "common knowledge among experts", it appears in many texts on the subject. I can easily cite one of the more prominent of them (Roskam) that I cited in another article. My problem is that so much conceptual error exists in the "Aero" subject areas that correcting calls louder than citing. It screams! :-). I haven't yet learned how to cite inline.  It's not that obvious how to do it, and the screams keep on distracting me!  :-).

--Gummer85 (talk) 20:06, 3 April 2009 (UTC)

"Simple Explanation" describes "Spiral Mode", not "Dihedral Effect"
This is an explanation for Spiral Mode which is important, but it is a superset and it isn't dihedral anything. However, it does contain within it "How Dihedral Angle creates Dihedral Effect" which is useful. The section should be retitled "How Dihedral Angle creates Dihedral effect" and rejiggered to explain just only that. I'll do that later if someone doesn't get to it first...

Also perhaps some other sections would be good like "How [fill in the blank] creates Dihedral Effect" for some of the other effectors (like wing sweep and all that other stuff). Please help here! :-)

--Gummer85 (talk) 06:55, 3 April 2009 (UTC)

Explanation for polyhedral on F-4 is wrong I think. (Nope, it's right.)
The explanation isn't referenced and isn't "common knowledge of experts". It's also inconsistent with the fact that there is SO MUCH ANHEDRAL on the "horizontal" tail. There is so much anhedral on the tail, it looks like a Viper from Battlestar Galactica!

The story I heard years ago was that they had to tip up the wing tips to provide wing clearance for landing on aircraft carriers (as the F-4 was originally to be both a Navy as well as Air Force airplane). The increase in polyhedral angle has the same effect as an increase in Dihedral Angle. That is, it increases Dihedral Effect. The airplane then had too much Dihedral Effect. To reduce it, they made Anhedral on the tail.

That's what I heard. It's much more plausible than the explanation in the article, but I don't have a reference (yet). The current entry really should be removed, but I don't want to "lose the space" and then forget to add the "correct" explanation after it is confirmed.

Also, I probably won't get around to confirming "my" story very soon. Can someone else look into it? (Is anyone out there? :-) )

-- Gummer85 (talk) 18:36, 4 April 2009 (UTC)

Whoops! I checked out F-4_Phantom_II quickly on Wikipedia and it corroborates the existing story. AND! It's referenced! I'll try to make the references a bit more clear. Chock one up for reference checking!

--Gummer85 (talk) 00:25, 5 April 2009 (UTC)

Change name to Dihedral (aircraft)?
I plan on changing the name of this article pretty soon if there aren't any objections. It'll take me a while to be sure anything that references it isn't broken, and to figure out exactly how to do that.

--Gummer85 (talk) 16:27, 20 May 2009 (UTC)

Why I reverted changes by Miket52
Hi Mike52,

I'm glad to see someone's actually watching and actually cares! :-) This whole time I've been essentially having a conversation with myself.  I reverted your edits though, for the reasons explained here.

Rolling moment caused by yaw rate is not Dihedral Effect, which by definition is Rolling moment due to Sideslip. Rolling moment caused by yaw rate is actually a different Stability Derivative called, well, "Rolling moment due to yaw rate" (funny how that is). These two ideas are very commonly mixed up.

The force couple (the difference in lift force on wings) is a moment as that is the definition of a moment. Moments and Couples are one and the same. I initially wrote "produces" myself, then I realized it was the moment. It's a small point, but more correct I think and makes it so we don't need to explain exactly how the couple produces the moment. Hmmm, maybe I didn't need to italicise the is, (less teachy that way). (I've rejiggered and improved this sentence to be a little clearer I think.)

The differential drag under sideslip conditions you speak of is a contributor to yet another stability derivative (Cn-Beta) called "Yawing moment due to sideslip". This is an important stability derivative which is also called "directional stability", but it is unrelated to Dihedral Effect except how they both contribute (in their own different ways) to the stability of the spiral mode.

The geometric definition of "dihedral" is covered elsewhere in wikipedia. The disambiguation note at the top points to the geometric definition. It would be good though to rename the article "Dihedral (aircraft)" to make it more clear.

--Gummer85 (talk) 15:50, 27 May 2009 (UTC)

"Common Confusion" section added
I added a "Common Confusions" section. I see these misunderstandings all the time in my pilot world and even among flight instructors and other near-experts. I thought it would be good to head them off at the pass.

--Gummer85 (talk) 16:49, 27 May 2009 (UTC)

Article name changed from "Dihedral" to "Dihedral (aircraft)"
I changed the name from "Dihedral" to "Dihedral (aircraft)" and properly rewired the references and redirections. All non-specific references go to Dihedral (disambiguation) whereas before they went here. This is to help people see that there is more on dihedral than this page and to help direct them to the most suitable location for their particular POV on dihedral (be it geometric, aircraft, etc.)

--Gummer85 (talk) 18:26, 27 May 2009 (UTC)


 * At my tagged request, an admin has moved Dihedral (disambiguation) to Dihedral, since there is now no need to disambiguate the DAB page's title. Please take this into considertation when you move an article from the primary topic to a DABbed title. In this case, an admin had to perform the move, since the original title was moved elsewhere. (This is a housekeeping role for admins, not because of something done wrong.) - BillCJ (talk) 22:24, 5 June 2009 (UTC)


 * Cool. :-)  --Gummer85 (talk) 03:58, 8 June 2009 (UTC)

Why I reverted edits by BillCJ
Hi,

Please don't think I'm possessive about this page. I thank you for your comments about admin actions for the name change. Also, I did indeed wonder what to do regarding capitalizing "Angle" and "Effect" and other editorial things like that. I gratefully seek guidance and improvement in that regard. There were some important changes in meaning you made that would have been better discussed here before making them. I reverted because that is the best way to correct them with no fuss nor muss.

In the last few months, I made changes and corrections to this article and explained every major change along the way here on this discussion page (and in detailed 255-character Edit Summaries). It was a discussion with myself, no one seemed to be responding so I had no choice but to see the changes as "acceptable" and "good". I am an aeronautical engineer and the changes are correct. The distinction between Dihedral Angle and Dihedral Effect is important and often confused. The main citation given (Roskam) is a well known reliable source and it verifies my explanations. I know people always like to see more citations. I can and will easily include some. However, the Roskam citation does indeed cover the corrections I made. In my opinion, it is quite adequate to justify the removal of the refimprove tag (although, I recognize that these questions are judgement calls).

In the future, I would love to discuss proposed major technical changes here before risking introduction of technical errors. I'm up for "explanatory" improvements too. My technical explanations are, I think, usually much better than those made by other technically-oriented people, but it sure does help to have a layperson's point of view to spot possible confusions that we don't see because things are just too "obvious" to us. :-)

Gummer85 (talk) 03:38, 8 June 2009 (UTC)

I looked over the changes more closely and I see the biggest change is the replacement of "Dihedral Angle" with "Dihedral" in a number of spots. The key problem with this article early on was the muddling of the two ideas of Dihedral Angle and Dihedral Effect. The ideas are muddled thoroughly in the minds of pilots and other people who brush up against this subject. Because of this, it is very important to separate the ideas crisply and cleanly and consistently. This is why the word "dihedral" must always be followed by "effect" or "angle". It's just that critical to understanding.

The other thing I noticed was the decapitalization of "angle", "effect", and "dihedral". I had given that some thought, and I capitalized them because I wanted to securely identify "Dihedral Effect" and "Dihedral Angle" as different concepts from each other. I also want them to be seen as entities in themselves. I thought that if "Effect" and "Angle" weren't capitalized, they could accidentally be seen as more associated with the word following it than with "Dihedral". The capitalization of both words was my invention to achieve those two goals. I know it's imperfect. I welcome other ideas here, are there prettier ways to achieve the same thing?

Gummer85 (talk) 06:59, 8 June 2009 (UTC)


 * Unfortunately, I found the article was somewhat confusing and inaccesible to an average reader with no engineering background. (Style issues aside - a reading of the Manual of Style might help with the basics on that.) However, I am fairly well-read in the aviation field in general, and usually the term "dihedral" is used to mean "dihedral angle," as far as I can tell, and that is what I was trying to make clear. Probably the best thing to do is to raise the issue at the WP Aircraft Project talk page, and get some broader input from other editors with more of a aviation/aeropace backgraound than I have. (There are several such editors active in the project.) They may have some solutions neither one of us have thought of, and was to make the article more clear without being confusing too (something my edits probably did not help.) - BillCJ (talk) 17:07, 8 June 2009 (UTC)


 * Neat. I've added the WP Aircraft Project talk page to my watch list.  :-)   -- Gummer85 (talk) 05:19, 9 June 2009 (UTC)

Isn't longitudinal dihedral more commonly referred to as decalage?
Should this be noted in the article? 69.250.53.240 (talk) 07:17, 11 July 2009 (UTC)

I dunno. I've never used the term, but it looks legitimate in a quick search, particularly as the difference between the angles of incidence of the two wings of a biplane. I had learned "longitudinal dihedral" in school and reviewed it in Roskam, so I added it in as another use of the word "dihedral" in the context of aircraft. Hmmm... Maybe "longitudinal dihedral" could be added to the entry on decalage? Would you like to do it? :-)

--Gummer85 (talk) 23:40, 7 August 2009 (UTC)

I've been looking further and it seems like "decalage" is used for biplanes and not as the difference between wing and horizontal stabilizer angles of incidence. "Longitudinal dihedral" in a general sense is the angle between two planes about the y-axis and so it could conceivably cover decalage, but I don't know if it is used that way. I think "longitudinal dihedral" applies to wing and stabilizer and that "decalage" applies to the two wings of a biplane. But, I'm just thinking out loud here. If you have a good reliable source about it, lets hear it! :-)

--Gummer85 (talk) 23:57, 7 August 2009 (UTC)

I'm having a hard time coming up with a concise reference. But I know from personal knowledge that decalage is used to describe wing and horz. stab. incidence in the model airplane hobby. I have also found a link to a mailing list posting where Dr. Mark Drela (MIT professor, aerodynamics) talks about decalage in that context. Googling for Drela and decalage turns up many other items. Drela is an expert in full scale aircraft aerodynamics and also well known for designing high performance model gliders.

I would love to help with the editing but I'm not sure what to do or how to approach it. I know there are lots of rules here on wikipedia and I don't want to break any of them or mess anything up. Are these references good enough or should I look for something more definitive?

Mailing List Posting



Dr. Mark Drela

--69.250.53.240 (talk) 05:05, 17 August 2009 (UTC)

Neato. I happen to be a member of the same RC club as Drela here in the Boston area (Charles River Radio Controllers). Those are some good references you found. It sure looks like Drela uses the term "Decalage" for what is called "longitudinal dihedral" here. As he is an aerodynamics god, I'd say that's a pretty reliable source. I wonder how much "decalage" is used in the "knowledgeable community". I'm a member of that community, but I'm knowledgeable enough to know where my knowledge ends. I think the term is pretty obscure, but I could be wrong. I've never needed to use it in my career. Maybe it's a "tail" vs. "empanage" kind of thing - just a different language. It's a good picture too, illustrating the difference between the chords and lines of zero lift. It's probably worth mentioning that "decalage is also used to describe longitudinal dihedral" and citing Drela. Go ahead and do it man! Make the change! Be bold! I can't babysit this article forever or by myself! Make the change and make the citations any cruddy old way you can, stick them right in the text if you need to. I'll neaten it up for you, you can see how that's done, then you'll know how to it next time! :-)

I think the strength of references need only be in proportion to the strength of the claim. The references show that Drela uses the term, not that "the term for X is Y" as in a textbook. So, instead of saying "Decalage is also a term for LD", it could be said "Decalage is also used as a term for LD". If Drela had written a textbook defining decalage as the longitudinal dihedral angle, I would say that's a pretty reliable source and would justify the "stronger" form ("Decalage is also a term for LD").

Now, if you happened to know for sure that Decalage is also a term for LD and is used and understood by knowledgeable practitioners, then in my opinion, it is okay to make the strong form of the statement and not fret about the citation too much, although it would be nicer to find a textbook reference as well to ward off 1) the unknowledgeable who think they're knowledgeable who think you're wrong, and 2) rabid citation demanders. In my opinion, in such a case, even with no citation, the "strong statement" would be verifiable simply because anybody can readily observe the fact that knowledgeable practitioners use and understand the word that way. That's my opinion and it's a point of contention however. I think it's okay to simply state such points as true and maybe find a good citation later. I think that's important because in Wikipedia Aerodynamics, the errors abound and the need for speedy correction of really awful mistakes trumps the need for simultaneous citation. Some disagree. Some think that if you say "the sky is blue" you need two reliable sources, and four pictures. In my opinion, when correctness is so wanting, it counts more than verification. Truth is self-verifiable (on testable "truths" such as these, not on untestable ones like how many angels can be stabbed with a pin).

Beware the use of aeronautical terms by RC guys and explanations from them. There are exceptions of course (like Drela). They're knowledgeable about some things, but there is a lot of misunderstanding among them that gets repeated so as to acquires an "air" of validity. RC "lore" is not a reliable source.

Gummer85 (talk) 00:43, 26 August 2009 (UTC)

Polyhedral or cranked?
This article uses the term "polyhedral" to describe what is elsewhere (e.g. here) called a cranked wing. Is there any precedent for that, and if so then which should we standardise on? &mdash; Cheers, Steelpillow (Talk) 20:48, 16 April 2012 (UTC)

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I feel like I've been scolded
Reading this article was like having someone wave their finger at me and tell me how wrong I am about everything. I came here to learn about this stuff, not to be lectured. What's worse, some of these explanations of the stability imparted by a positive dihedral contradict what I have read in textbooks by reputable publishers (e.g., Jeppesen Sanderson), yet these strongly worded and condescending explanations (contradictions) are not sourced. I came to learn about anhedral wings, and I got what I came for, but I could have done without the lecture. Dcs002 (talk) 06:29, 18 October 2019 (UTC)
 * Sorry, man. The truth is that info in pilot publications about the technicalities of aero engineering is often very wrong.  Often maddeningly so for me I would say.  You probably aren't wrong about everything, but about some things if you think Jeppesen is a reliable source for this kind of information.  Check out the sources in the ref list.  They're extremely well relied on by engineers -- and by you when you fly in a plane designed by those engineers.  The article does lack specific inline citations, but the refs it's based on are solid.  Usualzukor (talk) 01:10, 28 May 2020 (UTC)


 * Referencing aside, this page is written more like a lecture than an encyclopaedia. GraemeLeggett (talk) 07:12, 28 May 2020 (UTC)