Talk:Adverse yaw

A nonsense statement

The statement, "As it is the downwards deflection of an aileron that causes aileron drag, a simple way of eliminating adverse yaw would be to rely solely on the upward deflection of the opposite wing to cause the aircraft to roll." doesn't seem to make sense to me. The upward deflection of the aileron casus a reduction of drag and therefore should still exhibit the effect (albeit a lessor effect), so I disagree that it would "eliminate adverse yaw". zimmhead 17:31, 4 June 2006 (UTC)

You are right, edited. Meggar 04:01, 5 June 2006 (UTC)

Yep, good call. --Peter Kirkland 00:13, 17 June 2006 (UTC)

I found the statement "moreso on the lowered left side" confusing, because I was thinking in terms of wings, and of course moving the stick to the right lowers the right wing. It's clearer just to leave "lowered" out of the sentence. --Jrvz 12:50, 27 July 2006 (UTC)

[additional comment by PDR]

I would say the author has made an excellent job of explaining the actuality of Adverse Yaw, and a couple of the techniques that have been used to reduce it, without straying into the often controversial area of what causes it. I am very pleased to see no references to the frequently perpetuated (but utterly incorrect) explanations relating to different air densities above and below a wing. That gets this article a "well done" from me!

I would also like to add the important point that Adverse Yaw is not (as often stated) a "fault" in the design of the aeroplane, wing, ailerons or whatever - it is a "feature" which will always be present when a lifting body is rolled.

Pete Rieden

Causes

I have removed the mention of induced drag. As zimmhead points out above, the idea that the up-deflected aileron has decrease drag is inconsistant with the explanation of differential aileron action. Some old NACA studies of the subject support the statement that the up-deflected aileron generally has positive or neutral drag change. There must be more involved that just induced drag. Meggar (talk) 03:35, 29 November 2007 (UTC)

Additional comment

I'm afraid I'm going to have to disagree with you on this. The ailerons produce a rolling moment by increasing the lift on one wing and decreasing it on the other. The increased lift on the up-going wing gives a greater induced drag, and vice-versa on the down-going wing. It is this difference which produces a yawing moment.

[Additional comment by PDR 31-10-10] There is a misunderstanding on [at least] two levels here. Firstly whilst an upward-deflected aileron will reduce the lift coefficient and this reduce the induced drag, the defelcted surface will increase the FORM drag, usually by roughly the same or more as shown in the NACA studies. Secondly the wing only has unbalanced lift coefficients for a short, transient period while the aeroplane accelerates about the roll axis. the geometry of rolling is such that as the aeroplane rolls the helical path followed by the wing alters the angles of attack of each wing so as to reduce the roll moment. When established in a steady-state, constant speed roll the wings are once again at the same lift coefficient (obviously this is a simplification that considers an "ideal" wing and ignores the fifferent angles of the spanwise stations of the helix, but it is a good approximation that holds true in practice). The amount of aileron deflection required to *sustain* this roll is that required to oppose the helical change in angle of attack that opposes the roll. Peter Rieden [end PDR Comment]

When rolling left, for example, this will yaw the aircraft to the right. By raising the up-going aileron further to increase the parasite drag on that wing, it tends to produce a yawing moment in the opposite direction. Likewise, reducing the travel of the down-going aileron will serve to reduce the induced drag on that wing.

I propose that the comment mentioning induced drag is returned to the article.

I don't understand your (Meggar's) reason for removal of this explanation. Induced drag is an inescapable consequence of lift generation by a wing. It is a fact that reducing the lift of a wing will reduce the induced drag and vv. All other possible causes of adverse yaw can be avoided by careful design, but the change of induced drag is the fundamental cause and is unavoidable. When I get a moment I will rewrite the cause section to reflect this. treesmill (talk) 17:04, 29 November 2007 (UTC)

I will try to explain it better. Consider a case of extreme differential aileron action where the right alieron is deflected upward and the left remains at zero deflection. The lift on the right side decreases and the wing rolls to the right. Induced drag on the right side decreases along with lift producing a yawing moment to the left, an adverse yaw, proving that a differential aileron arrangement does not work. In fact it does work very well, telling us that there has been an incorrect assumption.

It is correct to say that induced drag is fundimental, inevitable, unreducable, and will always be a factor in yaw moment with any lifting wing while producing a rolling force. But it is not the predominant factor in the drag of wing with a deflected aileron. Actual wings and experimenental data show a more complex behaviour. If we must mention causes we will need a section covering more than a single insufficient explanation. Perhaps the article would remain more usefull as it is by stating the facts without going into causes. Meggar 03:03, 1 December 2007 (UTC)

I don't know what you mean when you say "proving that a differential aileron arrangement does not work". You state that "there has been an incorrect assumption" but you don't say what the incorrect assumption is. What you have forgotten is that any form of drag on the downgoing wing can be used to counteract the induced drag that causes adverse yaw. For example, spoilers can be, and are, used in some aplications for that purpose. In your example, the profile drag of the fully deflected aileron will do the job nicely, so it does work. You 'proof' depends on it not working, so the 'proof' fails. treesmill 12:53, 1 December 2007 (UTC)

I see that we are in complete agreement. The edit that I reverted, if you will check the history, was a mention of induced drag only. As you have restated above, the drag of an up-deflected aileron can result in a favorable yaw moment, countering and swamping the adverse effect of induced-drag yaw, and making an induced-drag explanation insufficient by itself - which is why I removed it. A user PDR has commented on this talk page about avoiding the often controversial area of causes. The two of us have demonstrated the wisdom of this by arguing about nothing. Meggar 02:21, 2 December 2007 (UTC)

You seem to have misunderstood a couple of things. As I demonstrate above, you are wrong to say that you have proved anything. The idea with Wikipedia is to add information where you feel something is incomplete, not to remove good information. treesmill (talk) 22:09, 5 December 2007 (UTC)

Not clear

To my understanding the up-going wing creates a greater angle of attack and therefore a greater lift component. As lift and drag are interlocked this creates more drag. In the drawing this is not made clear and the opposite (degreased angle of attack on the up-going wing) is shown. —Preceding unsigned comment added by John (talk • contribs) 08:14, 11 February 2010 (UTC)

[Additional comment by PDR 31-20-20]

There are two further misunderstandings in many of the comments on this page:

1. The purpose for using differential ailerons

Designers don't use differential aileron to counter adverse yaw (that's the pilot's job - we give him a perfectly servicable rudder to do it with). The designer uses differential ailerons to balance the lift coefficients of the two wings. Any cambered wing will usually exhibit different change-of-lift-coefficient-per-degree-of surface-deflection for upward and downward directions. This causes the roll centre to be somewhere other than the centre axis of the aeroplane, which is untidy. Differential aileron travel mostly addresses this problem.

2. The use of roll spoilers rather than ailerons

Spoilers are not used to prevent adverse yaw, they are used to reduce the torsional stresses on the aeroplane's wings. Modern aircraft generally save weight (aka "improve structural efficiency") by not having any great excess of torsional stiffness. They will often use structural *damping* as an alternative (the idea that was the original design justification for the podded engines of the Boeing 707). Ailerons impose large torsional loads on a wing because they act at the back end (technical term) of the wing structure. Spoilers act nearer the structural axis of the wing and so impose much smaller torsional loads. The poetential benefits in terms of structure weight can be quite large - easily a thousand pounds or so on an aeroplane the size of a Boeing 747. Peter Rieden

[End of PDR comment]

Misunderstanding

There seems to be a misunderstanding in the article. The 'adverse yaw moment due to roll rate' seems incorrect. It says the lift vector is perpendicular to the airflow, which is not correct. For convenience we can split the lift force into two perpendicular vectors, but the total combined force (which is what matters) is NOT perpendicular to the airflow.

It looks like this dubious image was introduced a few years ago, and then just recently someone has changed the article to say that this dubious "lift perpendicular to airflow" is the MAIN cause of adverse yaw.

It looks like the article was more correct a few years ago. See here for an example of a better (and correct) description of adverse yaw:

http://www.flightlearnings.com/2009/09/01/flight-controls-part-two-adverse-yaw/

--sciencewatcher (talk) 00:55, 31 July 2012 (UTC)

That diagram looks the same as the one from the FAA Pilot's Handbook. Along with all the other pilot training books I've read it talks only about aileron deflection as a cause of adverse yaw.

After seeing this article and the references it now gives, I was interested to learn that "adverse yaw is actually dominated by the aerodynamic yawing moment due to rolling" (Azbug & Larrabee p. 64). The deleted diagram certainly helped me to understand how a "moment is created as a result of the rolling of the wing itself" (Perkins-Hage p.330). I'll re-add it with more citations. Burninthruthesky (talk) 09:03, 11 December 2012 (UTC)

I also think this edit contained some useful explanation, including, "By definition, lift is perpendicular to the oncoming flow". That statement is correct, despite the contradiction above, used to justify its removal. Burninthruthesky (talk) 11:15, 11 December 2012 (UTC)

I've added some extra citations and footnotes. I hope this helps explain why the article differs from what many have been taught. Burninthruthesky (talk) 17:29, 12 December 2012 (UTC)

This section was extremely unclear for me to understand, and the citation was unhelpful due to its relative inaccessibility. Therefore, for the good of all of humanity, I have endeavored to explain the yaw moment caused by rolling motion in the clearest way I could. Unfortunately, the result is somewhat lengthy. However, I believe that this is necessary due to the way that the figure lacks any description whatsoever; all description must therefore be moved into the main text. BirdValiant (talk) 23:22, 19 February 2019 (UTC)

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