To Vortex Generate, or Not?

[Jungle]

I have been doing alot of research this last week on vortex generators like on placement and effectiveness and I had found a video last night that just absolutely amazed me. I HIGHLY recommend people interested in Vortex generators to watch this video. It is is a defferent language but that is fine. just watch it and see their test on a full scale and what they found with post stall improvements... I just could not believe it.
http://www.youtube.com/watch?v=2CmNhvT7LyE

 

[njswede]

Nice video, but it begs the question: Are they really flying post stall or are they just delaying the stall and allowing the plane to fly at a much higher alpha without stalling?

(Maybe this doesn't belong in Joe's forum, so feel free to move it. The topic is just too interesting for me to keep from replying... )

 

[Jungle]

Vortex Generators?

Agreed sorry joe but I thought it might help

 

[gyro]

I agree with you fellas, so I moved it for you.

 

[Jungle]

Thanks.

 

[njswede]

Thanks Gary!

So on a full-scale aircraft you want to avoid a stall in 99% of the cases, and it looks like that's what our German friends in the video clip are trying to demonstrate. However, as 3D flyers, we frequently want to induce a stall. That vortex generators delays a stall and allows a higher alpha seems to be pretty undisputed. But what do they do to 3D pilots?

I would assume that the main contributions they have is to make the stall more evenly distributed across the wing to avoid things like "tip stalls" and wing drops. Also, by retaining some laminar flow even at high alpha, I guess they would improve control surface response too.

So I guess the main question is how to place them. Should we keep them close to the fuse to take advantage of the prop wash and keep it laminar or should we place them closer to the tip to avoid the dreaded wing drop?

Mostly just thinking out loud here, but this is a topic that really intrigues me, so I'm eager to hear your ideas on it!

 

[teookie]

I recently flew commercial on one of those small, T tail planes with two engines in the back (embraer something or other), and i noticed that it had VG's on the wing, but only right in front of where the ailerons are located. Don't know what it means but i found it interested.

 

[njswede]

My uneducated guess would be that they're trying to make the airflow stay attached to the wing as it passes over the aileron to improve aileron response.

 

[Jungle]

Well right in front of the control surfaces are the best place I think for them but on the front of the airfoil that makes up the wing, like say maybe in the front 20% of the wing panel. This will keep a even flow of air at the trailing edge of a wing or surface in a post stalled situation. Or at least helps alot in this case. On commercial stuff I am sure they have done it to help it in control ability but not over exaggerate the use of them to prevent drag.
Where they help with 3d is your control surfaces will have more authority as they have a airflow across them post stall. The ail have to have some air to push against to work so you can see this this will help even if it is just a little. Also if the air leaving the trailing edge is smooth flowing and is not turbulent like behind and on top of a stalled wing then the tail surfaces also will have a cleaner airflow moving across them.
So with looking it like this then in 3d you will notice with a higher angle of attack and slower speed the effectiveness of your surfaces start to diminish. With the VG's you can , in theory, have a higher angle of attack at a slower speed and not see the effectiveness diminish. Also in non 3d flight you are having a more stream line effect on the air leaving the trailing edges of the wing providing the tail with clean airflow pattern.

 

[Jungle]

Keep in mind I have very little experience in vortex generators and I am only relaying information I have collected as I understand it. If someone has a better understanding or information showing something different please post it. I want to learn.