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# Alpha induced angle at 3D wing

## Alpha induced angle at 3D wing

(OP)
1)Does alpha induced really exist in real life or this is just mathematical concept for calculate induced drag?
(same as lifting line theory-circulation theory is just math concept for calcualte lift ,but everyone knows that airflow dont move around wing at circle...)

2)If exist in reality,how much is alpha induced in general,are we talking about 1-2degrees or more?
(I ask this, because I cant see change of airflow angle infront of leading edge when compare 2D vs 3D wing in wind tunnel..)

2)Why induced drag is shown by lift,ist be more logical to draw resultant force and then draw drag component from it?

### RE: Alpha induced angle at 3D wing

interesting, I'll look forward to reading responses.

for my part, and the last time I did any real aero work was before most readers here were born, I thought induced drag was a function/effect due to lift (a representation of tip vortex drag). I can't see why we'd vector sum this with lift, and then later vector sum in the other drag components of the wing ? although as I write this I see some logic in lumping the lift forces together (ie both lift and the drag component that is directly associated with lift). If so, then it's "just" an analytical artifice.

### RE: Alpha induced angle at 3D wing

Where did you get that diagram?
Just at first glance this doesn't seem right. It's not the typical presentation of lift and drag forces or their resultant.
It's a lot better to start with the basics, understand them clearly, then build. It think some underlying steps have been missed. Although what they are would take me some time and research to sort out. Before going to the effort, I'm posting this first just to let you know this looks "off" somehow.

What are you reading from? Some suggestions:
J.D. Anderson
Raymer
VonDoenhoff
Perkins & Hage
Kueth & Chow
Dommash, Sherby and Connolly

www.sparweb.ca

### RE: Alpha induced angle at 3D wing

The undergrad paper that reviews Drela code is probably the most complete of your search results, but the OP certainly can't get answers to his questions from that.

Please forgive me: Current circumstances have separated me from many of my books which are at my (locked) office. I seem to have badly chosen which ones to bring back to my home office and excluded most of my aerodynamics stuff.

You don't want answers from gut feel alone, so I hope someone can answer more rigorously. I'll just summarize that 1) yes induced drag is real. Wind turbines have substantial induced flow velocity effects and I have measured marked improvements in my blades by accounting for the effect of induced flow angle. And 2) the angle is dependent on the intensity of the induced drag, which varies along the span of the 3D wing, and varies with the lift coefficient (squared). When considering maneuvering flight with both high angle of attack and high velocity, I believe the induced angle can be quite substantial.

### RE: Alpha induced angle at 3D wing

There is upwash ahead of the wing for subsonic lift producing airfoils and the induced drag is part of the redirection of the lift component. It's been a while since Anderson, but it seems to fit.

As to the questions -
1) Yes it really exists
2) I don't know why you cannot see this.
2) Lift is always vertical for level flight so the diagram is just showing how the lift vector is transformed as part of the AoA transformation.

There is a beautiful image of this here: https://www.quora.com/What-is-downwash-and-upwash-...

### RE: Alpha induced angle at 3D wing

The wikipedia article on induced drag has a diagram fairly similar to the one the op posted. But...they go into more depth, and further down the article, show that the induced drag is proportional to the square of the lift, and inversely proportional to aspect ratio. Nobody in their right mind would try and compute the alpha-induced, it's not a relevant control input.

### RE: Alpha induced angle at 3D wing

#### Quote (3DDave)

There is upwash ahead of the wing for subsonic lift producing airfoils and the induced drag is part of the redirection of the lift component. It's been a while since Anderson, but it seems to fit.

As to the questions -
1) Yes it really exists
2) I don't know why you cannot see this.
2) Lift is always vertical for level flight so the diagram is just showing how the lift vector is transformed as part of the AoA transformation.

The typical definition of induced drag is the difference between the drag of an infinite wing and that of a 3D wing. Upwash and Downwash is present on a 2D wing, so to me it suggests the issue is that "Lift" is mislabelled in the digram it should something like total force vector which then breaks down in to lift and drag, induced drag has nothing to do with it.

### RE: Alpha induced angle at 3D wing

I am reminded that the effect also depends on the spanwise lift distribution, which has not been mentioned by the OP.

Which further suggests that the effect varies across the span of the wing; the calculated contribution being the collective effect and not a universal change everywhere along the span.

### RE: Alpha induced angle at 3D wing

induced drag depends on (among other things) Cl; thus there's some logic in vector summing with the "true" lift force.

personally, I'd sum the drag components together, sum lift and drag, then decompose into structural axes.

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