0
$\begingroup$

As seen in this picture, the tip vortices are said to make downwash. Why is that?

I’m also not sure why that’d tilt the lift vector backwards, but that might require a separate question.

Link to the article the picture is from. enter image description here

$\endgroup$
1
  • 1
    $\begingroup$ There are so many answers here about tip vortices, induced drag, tilted lift and so on, like this one or this one for example... $\endgroup$
    – sophit
    Mar 18 at 17:48

1 Answer 1

4
$\begingroup$

Your understanding is sophisticated enough that you shouldn't be trying to learn more from websites and other resources intended for pilots and laypersons. These resources do not apply sufficient rigor -- because rigor is not needed for that audience.

Instead, you should be learning from textbooks intended for engineers.

As you know, a wing can be represented by a horseshoe vortex system with a bound vortex at the quarter-chord line and two trailing vortices from the wingtips. These all have the same vorticity and can not exist without one another. Both the bound and trailing vortices contribute to downwash, but I think it is easiest to see how the bound vortex contributes.

I also personally do not like the description of induced drag tipping the lift vector backward -- lift is always perpendicular to the freestream. The total resultant aerodynamic force might be tipped backward, but not the lift vector.

$\endgroup$
9
  • $\begingroup$ I see. So the bound vortex is from the boundary layer, I think, and how would that contribute to downwash? I was going off of what this answer said. $\endgroup$
    – Wyatt
    Mar 18 at 17:31
  • $\begingroup$ @Wyatt: The bound vortex has nothing to do with viscosity and boundary layers. It is part of potential flow theory. $\endgroup$ Mar 18 at 18:15
  • $\begingroup$ @PeterKämpf oh right, I completely forgot about that haha $\endgroup$
    – Wyatt
    Mar 18 at 18:21
  • $\begingroup$ Also, I found this video. Do you think it's accurate? $\endgroup$
    – Wyatt
    Mar 18 at 19:46
  • 4
    $\begingroup$ @Wyatt Despite appearances, I don't have infinite time to spend here. In particular, I don't have time to watch arbitrary videos and score them for you. Videos like this one are likely mostly good. They probably get 95 or 99% of things correct. However, you tend to ask questions that poke at the last 1% or 0.1% of a subject. This is good -- as it demonstrates that you're really coming to an understanding. However, you can't expect a resource aimed at people who only care about the first 80% to meet your needs. $\endgroup$ Mar 18 at 21:22

Not the answer you're looking for? Browse other questions tagged .