Talk:Stall (flight)

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Umm..not an expert, but am an ex-fighter pilot. Just wondering why 'washout' needs to be folded into 'stall' section, when linking to it seems to work OK. Linking gives you the wonderful benefits of consulting any encyclopedia, namely the joy of discovering things such as 'washout' also describing an enema.

By coincidence, also describes what I felt like doing when I experienced a 'high-speed stall', (yes - yet another name for G-stall or accelerated stall) in a Jaguar, (not a car) at low altitude over Scotland.

If you're looking for a simple description of what a 'stall' is, how about the one advanced by my old flight instructor - "it's when your wing stops holding you up"

John

Contents 1 "G-stalls" 2 Complexity of introduction 3 Disambiguation 4 Image captioning problem 5 Birds 6 Simple Description 7 Proposed merger: Stall speed

[edit] "G-stalls"

I thinks this section is poorly written, unclear, and factually incorrect in some spots. Just for starters, it should be called "accelerated stalls," the much-more-widely used term, at least in the U.S. (Is G-stall a military or British term? Anyone care to chime in?). I will rewrite it. Anyone mind? Also, it might be a bit difficult to include just the right amount of detail. Would it be appropriate to go into a full-blown discussion of the V-G diagram in this article? I am leaning towards "yes." Vessbot 07:17, 25 Jan 2005 (UTC)

As its original author I feel a bit annoyed by your description of my writing - but go ahead, if you think it needs changing. Some additional contributions have been added since I put it in there, and to my mind the mention of centrifugal force is wrong and in error - we are talking only about WEIGHT, which increases in a turn. (If this sounds odd, then check your definition of weight - it's not MASS). Since lift must counteract weight then lift must increase in a turn; if the wing can't produce the needed lift then it will stall. I don't really see why this is hard to understand. G-stall is the term I've always used and heard from others, I'm from the UK. I don't think it's military term. Graham 05:18, 26 Jan 2005 (UTC)

You wrote: This is a condition where the wing cannot produce enough lift to support the aircraft's weight and centrifugal force, in spite of otherwise flying at a reasonable airspeed and angle of attack.

What does "reasonable angle of attack" mean? Stall will occur at the same angle of attack regardless of the G or speed. There is a simple mathematical relationship that equates the speed at which that will occur with the G/load factor.

"Significant amount of gee?" What is significant? A stall at any G above 1 is an accelerated stall by definition.

" In most types of GA aircraft, high-speed G-stalls are unknown because structural failure will usually occur before the G-stall condition could be met," ... ridiculous. See above. In the U.S., for example, the limit load factor for Normal category airplanes is 3.47 G's. Thus, if you stall a plane at any load factor between 1 and 3.47, that's an accelerated stall. That is sometimes practiced at the private pilot level here.

Vessbot 07:20, 26 Jan 2005 (UTC)

So fix it. Carping about it won't help, and just pisses people (me) off. Graham 05:16, 21 March 2006 (UTC)

[edit] Complexity of introduction

The introduction of this article would make sense to someone who already has a good understanding of the subject field, but I think it's perhaps too technical for a general introduction. Terms like "chord line", "angle of attack", "lift-coefficient", "angle-of-attack curve", "linear and nonlinear regimes", and "flow separation" are not in general use, but the article expects readers to understand them. While technical descriptions are certainly appropriate, there will be a lot of people coming to this article wanting to know what "stall" means and going away without an answer. Could someone knowledgeable about this topic possibly write a brief paragraph giving a basic overview to the uninitiated? -- Vardion 8 July 2005 22:41 (UTC)

[edit] Disambiguation

I'm going to turn this into a disambiguation page, then create a new 'Stall (flight)' page to cover this subject. There are too many legit other stall definitions, and the (flight) modifier will be consistent with other flight pages, such as Spin (flight). I'll move the discussion over to the new page so it stays with flying stalls, any objections? - Chairboy 20:36, 19 July 2005 (UTC)

Sounds like a good idea to me - go for it. Graham 01:20, 20 July 2005 (UTC)

I went for it. Created Stall (disambiguation) and put a link at heading of Stall (flight) to go to it. There are a bunch of pages that link to Stall that should have autolinked to Stall (flight), this method should reduce the workload that converting all of them would require. - Chairboy 16:35, 22 July 2005 (UTC)

This seemed needlessly tangled, since all the links to stall were meant to go to stall (flight). I created stall (enclosure) for all the other meanings and left a link at the top here, then moved this back to Stall. Thanks to those who started cleaning up links immediately; I got called away from the computer right after the move and came back to get started with cleanup only to find most of it done! Thanks, — Catherine\^talk 19:18, 3 March 2006 (UTC)

Just because some aircraft enthusiasts (me included) have created the most links to stall doesn't mean that Catherine is right. 90% (very approx) of the time "stall" is used it's engine stopping the general pop'n has in mind; 10% it's enclosures; 1% it's aerodynamic. When someone comes to the Wikipedia article then disambiguation is required. I think Chairboy's treatment is correct. I will wait a while and re-do his changes. And then I will hunt out double redirects in aviation articles and replace stall with stall. OK? You can help if you like. Paul Beardsell 09:26, 2 September 2006 (UTC)

OK, I did that and I am currently working through the double redirects. Paul Beardsell 16:39, 30 September 2006 (UTC)

[edit] Image captioning problem

The recently added image includes a caption "tilt with respect to horizontal plane". Thus MUST be changed to "tilt with respect to airflow", otherwise it is simply incorrect. In addition, the images themselves are a bit misleading to my mind. An unstalled wing shouldn't be shown with a trail of turbulence left behind, since this isn't there. The flow is smooth. Graham 05:37, 13 February 2006 (UTC)

On further thought I decided to temporarily remove the image from the page. It can be reinstated once the problems are fixed. I decided to do this because anyone coming to this article with this image in its current form will leave with the wrong information. We don't want that to happen, and since the text is OK, this is the best way forward that I can see. Graham 05:40, 13 February 2006 (UTC)

The more I think about it, the more troubled I am by this image. I think it should not be reinstated. I have written a criticism of it at Image talk:StallFormation.gif. Most surprising is that the image was sourced from NASA - they ought to know better than this. Graham 05:50, 13 February 2006 (UTC)

Wow, that is bad. I don't know aerodynamics very well, but maybe we can patch things up with Photoshop. I've uploaded two new versions, one with the "with respect to airflow" change, because that's blindingly obvious. The latest version has an additional airfoil diagram at the top for 0° that says "laminar flow, no turbulence". Does that latest version of Image:StallFormation.gif look correct? --Interiot 09:50, 13 February 2006 (UTC)

Good work on the caption. Unfortunately I'm still unhappy about the rest. There simply is no "separation point" in existence until the onset of the stall - so the images at 4° and 8° are still wrong. I'm not even sure that the approach of describing the stall as an existing separation point moving forward is going to get us anywhere, especially as the article itself doesn't take this approach - in fact "separation point" isn't even mentioned. At the onset of the stall there is an airflow detachment or separation, but it comes into being at that time - yes, it moves from the trailing edge forward as the AoA increases, but this change occurs over a very narrow range of angles close to the stall (say from 15° to 17°). AoA less than that are fully laminar. I think NASA must have commissioned this artwork from a graphic artist who was given a rough description to go on with few details, and basically got it wrong. A simple fix would be to change the captioning of the angles - change 4° to 15°, 8° to 15.5°, etc, but a better fix would be to change it more radically by showing the more conventional "airstream" lines that usually are used (in fact, that's another thing - the portrayal of the turbulence here looks like the wing's on fire or something - it doesn't properly illustrate what is happening all around the wing.) However, let's get some other views on this before entering into a load of edits. It might even be better to start over - I might look into doing it myself if I can make the images look decent. Graham 22:23, 13 February 2006 (UTC)

Yeah, I don't fully understand the topic myself, but have a bit of Photoshop experience, and would love to find/create an image as necessary. Okay, next proposal: we just have two wings, one at 13° that shows 100% laminar flow lines around the wing (eg. like this). And then below that, a wing marked "15°, stall point", something like what's there now or this or this, with the laminar flow lines going around the wing, except for the separation region. Also, if the article doesn't mention "separation point", should that phrase be left off? Or, I've seen other pages [1] [2] refer to it as the "transition point" as well, would that be more appropriate? --Interiot 23:59, 13 February 2006 (UTC)

Sorry to challenge what some of you have written, but as an Aeronautical Engineer I have to say some of the statements above are wrong. To begin with, unstalled wings often DO leave a turbulent wake behind. A wing that is 100% laminar wouldn't leave a wake, but these are practically impossible - almost all wings are turbulent, and so leave a wake behind, even in normal unstalled flight. This turbulent wake accounts for a significant portion of the aircraft's drag. Secondly, the 'separation point' nearly ALWAYS exists on a wing. As shown on the image here, it's the point at which the boundary layer 'trips' from laminar to turbulent, increasing dramatically in thickness. This point exists on all normal wings, and is not related to stalling. --dSpammer 22:00, 13 August2006 (BST)

If you are willing to make the images, that would be great. I started to have a go but I got very frustrated with the free dumbass drawing package I was trying to use (Eazydraw) which makes drawing basic bezier curves unnecessarily complex. Anyway, I think your proposal sounds good - an unstalled wing at some angle (it doesn't need to be 13°, anything reasonable - say 6°, which is a typical AoA in straight and level flight) with laminar flow lines and no turbulence, separation point or any of that malarkey. Then a wing partially stalled (15° say) where the flow is laminar over the first half or so, then breaks away, and one fully stalled where the flow is not attached at all, and spills over the leading edge. Those photographs you linked are very informative and could well be used as a basis - the depiction of turbulence is difficult and just using hatching is a bit lame - some sort of eddying would be great. I think we should avoid using any captions that mention 'separation point' - it should be obvious from the drawings that the airflow has detached and that ties in with the description in the text. Graham 04:24, 14 February 2006 (UTC)

Okay, the image isn't perfect, but I uploaded a new version. Since I don't even know what a proper airfoil is really shaped like, it's a more conservative modification of [3]. If there's a good sharp image of what turbulence looks like, I might be able to trace that. But is the latest version of the image semi-acceptable? --Interiot 18:38, 25 February 2006 (UTC)

Much, much better. The only comment I'd make is that in the 25° case, the separation point could be right "on top" of the foil's curve, rather than further back as it is now, but if it's a lot of work to change it then it's acceptable anyway. Graham 03:21, 26 February 2006 (UTC)

Done. Although note that the 25° one was previously unmodified from the original image, so it may have been okay as it was before too. --Interiot 20:18, 26 February 2006 (UTC)

==re the suggestion that Washout be merged with Stall== I think there needs to be a subject on Washout but my comments in Washout about the terrors of wing tip stall should be located under the general heading of Stall. When I changed Washout I was trying to correct the previous version which suggested the sole reason for washout was to optimise wing efficiency ie reduce induced drag, whereas avoidance of tip stall, which is more important, wasn't addressed. So I changed the text leaving the structure unchanged. Now, what about the Stall section? It seems to me that a few changes are needed. Take the first sentence "In aerodynamics, a stall is a condition in which an excessive angle of attack causes loss of lift due to disruption of airflow". Read this through the eyes of someone who really wants to know what 'stall' is ie doesn't know already. Do we really mean that excessive AofA causes LOSS of lift? LOSS of lift? Is it leaking away? Or do we mean that the lift is less than would have been achieved were the wing not stalled? If the latter, why don't we say that? Also the discussion above re the diagram seems to suggest that there are only two airflow regimes, laminar and separated. Laminar is very, very difficult to achieve and not possible with an aerofoil section like that shown in the diagram. What will arise at angles less than the critical angle is turbulent (but not separated) flow. --FHBridges 19:03, 1 March 2006 (UTC)

So do you want the article written for the layman or the expert? My view is that it's the layman we are writing for every time, though having said that it doesn't mean being patronising and omitting important detail where warranted. I agree with your comments about the explanatory paragraph being not very enlightening to the uninitiated, but then introducing complexities such as truly laminar flow being rare is going too far the other way. In simple terms the laminar = unstalled, separated/turbulent = stalled equation is valid, and that's good enough to get you a very good appreciation of what a stall is, if you don't know anything about it. Anything more than this is detail, and while some detail is good, getting into discussions about nuances of aerofoil shape and what truly laminar means and so forth isn't to my mind going to be very helpful. You can get 99% of the way in a few sentences - the remaining 1% we can leave to the expert texts aimed at graduates studying aerodynamics, who we most definitely are not writing for. Graham 03:36, 2 March 2006 (UTC)

The articles need to be written for the layman. I didn't suggest adding complexity by discussing the problems of achieving laminar flow - it has no relevance to this topic. But I disagree with your equation of laminar = unstalled, separated/turbulent = stalled. The flow around an aeroplane isn't laminar it is turbulent. Turbulent flow is understood to mean turbulence which is small in scale compared to the body in question. My objection is the use of the terms 'laminar flow' and 'turbulent flow' in the figure . Laminar flow is the holy grail of aerodynamicists - if it could be achieved the effect on aviation would be enormous. It would be wrong to imply that it is commonplace. Turbulent doesn't equate to stalled. Better descriptions would be 'steady flow' in place of 'laminar flow' and 'separated flow' in place of 'turbulent flow'.--195.93.21.5 19:13, 2 March 2006 (UTC)

Oops. I composed the above without signing in. Didn't realise you could do that! Didn't intend to be anonymous. --FHBridges 19:21, 2 March 2006 (UTC)

I concur with that - perhaps our friendly illustrator could do one more iteration of the drawing? Graham 22:59, 2 March 2006 (UTC)

How's that? I'll try to keep the latest versoin of the .psd posted too, in case others eventually want to make changes. --Interiot 02:24, 3 March 2006 (UTC)

Back to the original subject - washout. I recommend moving it to the entry for "Wing". Because it does not just apply just to aerodynamic stall issues but also to aerodynamic efficiency, I believe it fits better there than under "Stall". Then it can be linked to "Stall" and vice versa. And it really shouldn't be sharing a page with railway info and an entry about Jamaican purgative practices, eh? Hatcat 17:11, 22 March 2006 (UTC)

[edit] Birds

I have a bird book at home, which details how aq bird can stall in flight.

Is this notable?

Because I notice this article only discusses powered flight.

[edit] Simple Description

Stall

Is when the wings of an aircraft are no longer capable of deriving enough support from the air in order for the aircraft to maintain altitude. Although a stall usually occurs at slow speeds with excessive nose up attitudes it can actually happen over a wide range of speeds and attitudes.

There simple and to the point. Everyone agree with my definition? (contributed by User:43R35)

I like this simple definition. The subject can be as complex as you like. But, considering the number of words used, that would be the best paragraph of the whole article (many of which are seriously in need of improvement). I suggest you insert it as the introduction. EDIT BOLDLY! Paul Beardsell 09:39, 2 September 2006 (UTC)

Sorry, no. Every aircraft descending from cruise altitude to landing is "no longer capable of deriving enough support from the air in order for the aircraft to maintain altitude", but it is not stalling. It is simply that the lift being generated by the aircraft is less than it's weight. --dSpammer 22:05, 13 August2006 (BST)

Not correct. If lift is less than weight then there is an imbalance of forces and acceleration in the direction of the imbalance occurs. Not movement but acceleration. It's Newton 2. E.g. That an aircraft moves forward at a steady speed does not mean thrust exceeds drag. (Should one not understand that then one is not qualified to comment.) Similarly: If an aircraft is descending at a steady rate (say 500 ft / minute) this does not mean the (vertical component of) lift is less than weight. Should dSpammer pull back on the controls he will find that his previously descending aircraft was indeed creating enough lift to maintain altitude. Of course, the aircraft will, after levelling off, start to slow down and will eventually stall if thrust is not applied. Descending is simply another way of maintaining airspeed - it's a substitute for missing thrust. So dSpammers criticism of the suggested para is not valid. Paul Beardsell 09:56, 2 September 2006 (UTC)

However, there are many paras in the article which are in need of severe editing. Paul Beardsell 09:39, 2 September 2006 (UTC)

[edit] Proposed merger: Stall speed

A proposed merger of Stall speed into this article has been sitting around for over a year. It makes sense to me, and shouldn't be too hard to accomplish. Any problems? PubliusFL 19:58, 10 January 2007 (UTC)