Talk:Lift-induced drag

message: ==Untitled==
According to what is written it could be understood that there is two sources of induced drag:
Due to lift generation( could be understood that it appears in 2-Dimentional flow)
Due to tip effect (could be understood as 3-Dimentional since tip vortices are 3-d)
the question is:
*what is the equation of induced drag in 2-D flow?
*what is the equation of induced drag in 3-D flow?
IF ANY ONE CAN HELP ME please mail me at mohamadcharif@yahoo.com —Preceding unsigned comment added by 193.227.168.132 (talk) 08:28, 14 April 2004 
The 2-D flow means the same as a wing od infinite span  to chord ratio - and in this case the lift induced drag is zero.
In real 3-D case induced drag is the function Ci=(Cy)^2/Pi*A and is caused by the tip vortexes (mainly) and other trailing vortexes.
andrzejmat 16:13, 7 April 2006 (UTC)

message: I'm thinking of adding this, early in the article:  "Lift induced drag is caused by the lift component of the wing being rotated backwards relative to the aircraft's motion, resulting in a drag component."  Seem reasonable? Mat-C 16:31, 24 August 2005 (UTC)
replies: text: This is how the article originally defined Lift-Induced drag, but since then others have taken issue with this approach saying that it's an over-simplistic picture and not reflective of what's truly going on. If you check through the history you'll see this, inclusing a diagram (which I drew) which is no longer used in the article. Graham 00:11, 25 August 2005 (UTC)
thread_title:  Simplification 

message: "k is the factor by which the induced drag exceeds that of a wing of infinite span typically 1.05 to 1.15" is not true of course. Not" a wing of infinite span", but should be there "a wing of otimum (eliptical) planform."
andrzejmat 16:13, 7 April 2006 (UTC)
thread_title: Error

message: In this I chose to Undo the immediately prior edit on the grounds: 1) The wingtip vortex is not the Source of induced drag, it is a manifestation of the spanwise flow which is the Source. 2) The later section of the Undone text essentially repeated what was previously said in the Section.
While it is true that the energy content of the tip vortex is equal to the energy loss due to induced drag, and of mathematical value to the aerodynamicist, it is confusing to a lay reader to see two apparently conficting statements as to the source in the section 'Source'.  Geoffrey Wickham 05:32, 9 October 2007 (UTC)
thread_title: "The wingtip vortices do not directly cause induced drag". Edit of 05.10,  9 October 2007

message: The article says Unlike parasitic drag, induced drag is inversely proportional to the square of the airspeed.
This is not strictly true.  It has the unstated assumption that the lift coefficient is inversely proportional to the square of the airspeed.  This is certainly true (only because the pilot actively makes it so) for an aircraft that is flying straight and level.  It is not true for a wing at constant angle of attack with constant CL.  I think the statement needs to be qualified (as well as the equations given below it about CL), or revised. 
Perhaps this represents the difference between the mindsets of pilots and engineers =)MarcusMaximus (talk) 10:05, 16 September 2008 (UTC)
replies: text: I attempted to fix that problem. I'm fairly confident my fix isn't wrong. Fresheneesz (talk) 23:32, 23 September 2008 (UTC)
thread_title: Inversely proportional to airspeed

message: Cdi is given as K*Cl^2/Pi*AR. This is incorrect. The correct form is K*Cl^2 OR Cl^2/Pi*e*AR. This is because K = 1/Pi*e*AR. To clarify, Cdi= Induced drag Coefficient, K = drag polar constant, Cl = Coefficient of Lift, e = Oswald efficiency factor, and AR = aspect ratio. Mathiusdragoon (talk) 14:40, 22 May 2009 (UTC)
thread_title:  Definiton of Cdi 

message: I saw 206.55.186.247's changes and I liked them.  I had been thinking about that change myself.  Kinetic energy imparted into the downwash/vortex field is the fundamental source of induced drag.  There's nothing magical, it's just an energy/power balance.  When AR is infinite, there is no energy in the downwash/vortex field, and there is no induced drag.
Also, the "tilting lift vector" explanation is time-tested, but it's crap.  It is akin to the "equal transit time" model.  That is, it's right in some ways giving it the illusion of validity, but it's wrong in fundamental ways and it's incomplete.  The tilted-lift vector begs more questions than it (supposedly) answers.
:1) The explanation should start with the fundamental source of induced drag which is:
:For a constant downward rate of change of momentum (constant lift in opposition to constant weight), more kinetic energy is put into the downwash (+vortex) field as the cross section area of the downwash field becomes less.  Both reduced AR and slower speeds reduce the cross section area of the downwash field.  Reduced AR reduces the cross section area of the downwash field because for a constant wing area and planform shape, reduced AR means reduced wingspan.  The crossflow dimension of the downwash field is closely equal to span.  The cross section area of the downwash field is also reduced at slower speeds (higher Cls).  In this case, the cross section area of the downwash field is reduced along the direction of flight.  That is, for a given amount of momentum (impulse) imparted downward to the air, the plane travels a shorter distance.
:The fraction of kinetic energy put into the vortices compared to the downwash field (and its increase with reduced AR + slower speed) may or may not have much to do with spanwise flow (I'm skeptical in this regard, although I suspect it has something to do with sub-optimal (non-elliptical) lift distribution and Oswald efficiency).  I'm still muddled with regard to the amount of K.E. in the vortices vs. the actual downwash field, but in this model, K.E. in both the downwash field and vortices becomes zero when AR becomes infinite.  When AR is infinite, downwash speed is zero (no K.E. lost there), and there are no vortices (no K.E. lost there either), and induced drag is, well, also zero(!).
:2) After the fundamental source of loss of energy (and power) is discussed, the mechanism by which this alters the total aerodynamic force (and it's component drag) should be discussed.  That is, exactly how is more drag induced as more kinetic energy (power) gets put into the downwash/vortex field?  What are the complete and consistent mechanics of it?  This is an area I am unfamiliar with and could use some help on.  The tilted lift vector is inadequate here.  It doesn't give the amount of change to local AOA which would be needed to support the "inversely proportional to speed" wording.  Somewhere out there in the reliable literature someone must have thought about this well and explained it well.  (I emphasize "reliable" because much of our literature merely promulgates galloping error.  Just because it's at a NASA web site doesn't make it reliable.  We oughta know better.)
:3) Last, a discussion of how "everything effects everything else" until an equilibrium is settled into.  This is something missing in a lot of our "aero" explanations.  Sure, "vortices produce downwash" but downwash also produces vortices and so on and so on, for a simple example.
I'm still working this "correct & complete" understanding out in my own head.  I've still got holes in my own understanding here (not in my head :-) ),  The more we know, the more we know about what we don't know.  I do know however, that much of this article as it stands is diversionary not explanatory.  People can easily come away thinking they understand when they actually don't.
--Gummer85 (talk) 19:41, 29 May 2009 (UTC)
thread_title:  I call "flakey" on this article. 

message: "Lift" is the component of the pressure-gradient force that is perpendicular to the relative wind; "Induced Drag" is the component that is parallel.  The vector diagram at the beginning of the article labels the entire pressure vector as "Lift", which is just wrong.  — Preceding unsigned comment added by 69.138.184.248 (talk) 19:43, 13 August 2011 (UTC)
replies: text: It has been removed. Eric Kvaalen (talk) 08:52, 16 December 2013 (UTC)
thread_title:  "Lift" in First Diagram is Wrong 

message: Is anyone actually reading this discussion?  Helloooo?  — Preceding unsigned comment added by 69.138.184.142 (talk) 23:25, 24 December 2011 (UTC)
replies: text: Also removed. Eric Kvaalen (talk) 08:52, 16 December 2013 (UTC)
thread_title:  "Lift" in Second Diagram is Also Wrong 

message: The edit made by 157.127.124.15 on 23 July 2012 states:
"Of course the best way to reduce flow around the wingtip would be to have the winglet horizontal to provide lift from the extended wing, but this approach restricts the number of hangers that the aircraft may use."
The addition of this statement seems erratic in the context of the paragraph and conceptually wrong. Getting lift from this "horizontal winglet" would also generate induced drag. I might be able to accept a nonlifting airfoil as the horizontal winglet but this seems impractical, and would degredate lift on wing surfaces below the 'winglet'. I have been unable to find an example of this. Perhaps i'm interpretting this wrong.
lastly: "this approach restricts the number of hangers that the aircraft may use" - this is silly.
Thoughts? I'm going to remove this.
Viola00 (talk) 20:16, 26 February 2013 (UTC)
replies: text: I agree that the edit did not improve the quality of the article, especially as it was unsourced. Thanks for erasing it. Dolphin (t) 23:32, 26 February 2013 (UTC)
thread_title:  Horizontal winglet edit 

message: I removed the unreferenced mention of wing fences from the "Reducing induced drag" section. http://www.aerospaceweb.org/question/aerodynamics/q0228.shtml, referenced at wing fence,  says fences create vortices to delay wing stall, but vortices also create drag. Can fences reduce induced drag? Burninthruthesky (talk) 19:37, 2 May 2015 (UTC)
replies: text: Anything that alters the spanwise lift distribution so that it more closely resembles an elliptical shape will reduce the lift-induced drag. I can imagine wing fences causing jump discontinuities in the spanwise distribution but I can't imagine them promoting an elliptical distribution. Therefore I think we have to be sceptical about any claim that they reduce lift-induced drag. Besides, lift-induced drag is more of a problem in low-speed aircraft whereas fences are mostly a device for dealing with problems in transonic and supersonic aircraft. Dolphin (t) 07:14, 3 May 2015 (UTC)
thread_title:  Wing Fences 

message: Hi, I'm trying to help improve this article, and I had a lot of changes reversed, which I understand because I made a lot of them. 
So I'll just start with my questions, suggestions, changes one at a time to start the discussion. 
I like the topic introduced in "Minimum induced drag for generic non-planar systems" section, and want to keep the final figure: "Nonplanar wings: results", with the text to introduce it.  "Demasi Luciano et al discuss the efficiency of nonplanar wings.  Here the efficiency is the ratio between its aerodynamic efficiency and the efficiency of a cantilevered wing with the same wing span and lift."<ref>
But the rest of the section seems to be a simple paste of a few paragraphs from a thesis/paper, and not at all in encyclopedic style or level.  I propose the rest of this section be deleted.  Any objections?  
Hess88 (talk) 02:08, 15 April 2016 (UTC)
replies: text: I think the non planar section would better illustrated by this article: http://adg.stanford.edu/aa241/wingdesign/nonplanar.html Pictsidhe (talk) 14:00, 17 July 2016 (UTC)
thread_title:  Thesis material crammed in as section "Minimum induced drag for generic non-planar systems" 

message: This famous diagram labels the backwards component of the aerodynamic reaction force "induced drag". However, isn't that wrong? I think this backwards component should be labelled "total drag". cagliost (talk) 12:30, 25 March 2022 (UTC)
replies: text: The diagram is correct. See the discussion above under the sub-heading “Diagrams”. Dolphin (t) 13:41, 25 March 2022 (UTC)
thread_title:  Diagram incorrect?