Rear Wing Idea

[Pierce89]

Wow! As a person working on a double major in mechanical and aeronautical engineering, I'm really uncomfortable in this thread. You people are just slinging half truths and downright incorrect assertions all over. A lift generating wing of infinite AR will still produce induced drag because of the pressure differences on each side.

[turbof1]

Wow! As a person working on a double major in mechanical and aeronautical engineering, I'm really uncomfortable in this thread. You people are just slinging half truths and downright incorrect assertions all over. A lift generating wing of infinite AR will still produce induced drag because of the pressure differences on each side.

Could you perhaps give us a better equation to work with? I fully agree that the current equation is too simple.

[trinidefender]

Yeah I was in a hurry. Do we have a good drag formula for conventional aerofoils? From an other website, there's this very simple formula:
http://www.propdesigner.co.uk/assets/im ... rag204.gif
Again, very simple and very theoritical (duh, as we are speaking about infinity in the first place). Again, the whole formula is getting devided by consequent A.R. .

(Of course again this isn't relevant to real life wings and relevant to the discussion at hand, doesn't count in induced drag by wing tip.)

There's also this that looks like a very interesting article:
http://www.grc.nasa.gov/WWW/k-12/airplane/induced.html

Again the theory falls short on the fact that the wing tip produces induced drag too. What I think is that moving the A.R. to infinity, wingtip induced drag becomes a constant for a given chord.

I actually posted that very same link on either the first or second page of this topic. But again, they say it there; "For a wing, the total drag coefficient, Cd is equal to the base drag coefficient at zero lift Cdo plus the induced drag coefficient Cdi."

"Cd = Cdo + Cdi"

I said he same thing just in more lengthy terms, "The way you can think about it is induced drag is only zero (in any direction) if the lifting force is also zero. The moment you introduce a lifting force (on an aircraft through the action of increasing angle of attack on the wings) induced drag starts to take effect."

So yes I guess the real conclusion we have come to is that by having an infinite wingspan there is obviously no spanwise flow. With no spanwise flow and the theoretical infinite wingspan it becomes almost impossible, especially with our limited resources, to accurately model theoretical physics. (Reading that in my head made me laugh a little that we have even reached theoretical physics). Do you guys, and girls, agree with me on that?

Now an interesting thing and to bring this full circle back to F1 is, if you look at it, the closest thing to an F1 wing in aviation is a closed loop wing. Here is a link with some pictures of a working plane that has a wing like that http://englishrussia.com/2009/03/05/ellipse-wings/

If anybody is up for a bit of reading take a look at this, http://aero.stanford.edu/reports/VKI_nonplanar_Kroo.pdf

I didn't finish it yet but it is about closed loop wings and it may help us to understand the dynamics of the rear wing better.

[trinidefender]

Wow! As a person working on a double major in mechanical and aeronautical engineering, I'm really uncomfortable in this thread. You people are just slinging half truths and downright incorrect assertions all over. A lift generating wing of infinite AR will still produce induced drag because of the pressure differences on each side.

Your point about an infinite AR wing still producing induced drag is what I have been trying to say.

I am curious though. What other "half truths and downright incorrect assertions" do you see?

[Pierce89]

Wow! As a person working on a double major in mechanical and aeronautical engineering, I'm really uncomfortable in this thread. You people are just slinging half truths and downright incorrect assertions all over. A lift generating wing of infinite AR will still produce induced drag because of the pressure differences on each side.

Your point about an infinite AR wing still producing induced drag is what I have been trying to say.

I am curious though. What other "half truths and downright incorrect assertions" do you see?

Mostly from the people arguing against you on various matters. It seems you're one of the people actually worth reading.

[variante]

Then could you give us the precise definition of induced drag? How does it manifest? Does it exist in infinte wingspan conditions?

[turbof1]

Yeah I was in a hurry. Do we have a good drag formula for conventional aerofoils? From an other website, there's this very simple formula:
http://www.propdesigner.co.uk/assets/im ... rag204.gif
Again, very simple and very theoritical (duh, as we are speaking about infinity in the first place). Again, the whole formula is getting devided by consequent A.R. .

(Of course again this isn't relevant to real life wings and relevant to the discussion at hand, doesn't count in induced drag by wing tip.)

There's also this that looks like a very interesting article:
http://www.grc.nasa.gov/WWW/k-12/airplane/induced.html

Again the theory falls short on the fact that the wing tip produces induced drag too. What I think is that moving the A.R. to infinity, wingtip induced drag becomes a constant for a given chord.

I actually posted that very same link on either the first or second page of this topic. But again, they say it there; "For a wing, the total drag coefficient, Cd is equal to the base drag coefficient at zero lift Cdo plus the induced drag coefficient Cdi."

"Cd = Cdo + Cdi"

I said he same thing just in more lengthy terms, "The way you can think about it is induced drag is only zero (in any direction) if the lifting force is also zero. The moment you introduce a lifting force (on an aircraft through the action of increasing angle of attack on the wings) induced drag starts to take effect."

So yes I guess the real conclusion we have come to is that by having an infinite wingspan there is obviously no spanwise flow. With no spanwise flow and the theoretical infinite wingspan it becomes almost impossible, especially with our limited resources, to accurately model theoretical physics. (Reading that in my head made me laugh a little that we have even reached theoretical physics). Do you guys, and girls, agree with me on that?

Now an interesting thing and to bring this full circle back to F1 is, if you look at it, the closest thing to an F1 wing in aviation is a closed loop wing. Here is a link with some pictures of a working plane that has a wing like that http://englishrussia.com/2009/03/05/ellipse-wings/

If anybody is up for a bit of reading take a look at this, http://aero.stanford.edu/reports/VKI_nonplanar_Kroo.pdf

I didn't finish it yet but it is about closed loop wings and it may help us to understand the dynamics of the rear wing better.

Just to be clear: Cdo is friction drag + form drag right? Which isn't induced drag.

What I gather ultimately out of it, is that the equation is very misleading. Induced drag will still be present when AR goes to infinity, due pressure difference (if lift is produced). The formula doesn't reflect that. Is there an equation that factors in lift?

[trinidefender]

turbof1 read the sentence above the formula that I quoted. "base drag coefficient at zero lift Cdo" therefore Cdo is all drag created that isn't created in the production of lift, or in Formula 1's case, downforce.

If you want to get into a lot of detail there are many other forms of drag. In aviation all these other forms of drag come under the broad term of parasitic drag.
Parasitic drag is then generally broken down into a few different things.
- Form drag: basically the size and shape of the object that is presented to the airflow. Things like streamlining of bodywork and such reduce this.
- skin friction: fairly self explanatory, the drag created by the friction from the skin. If you want to see a good example of skin friction drag reduction then look at the dimples on a golf ball. Also the general roughness factor of a surface and the drag associated with it.
- there is also interference drag: this is drag created by airflows from two different surfaces trying to occupy the same area. You see this a lot at places where there are acute angles such as between the rear wing and the end plates or on aircraft at wing roots and similar. That is why aircraft manufacturers generally try to create a smooth transition between the wing and the body.

*note* there is also a 3rd major type of drag which is called wave drag, wave drag also does not fall into the category of Cdo but we don't use it and I shall explain why. This however shouldn't really apply to Formula 1 because it is drag created from pressure waves as you approach and go past the speed of sound. As such you won't really hear it being discussed.

Now onto your next question which deals with the theoretical infinite wingspan. Think of it this way. If there is an infinite wingspan then there would be an infinite surface area and an infinite amount of lift and finally and infinite amount of drag produced.

What I think you are asking is. Is there a formula you can use to find the lift and drag forces FOR A DEFINED SECTION of an infinite wingspan wing? Is that what you are asking? If so, then no I do not have a formula for that. Pierce might.

[NoDivergence]

I may have stepped in here at an inopportune time, but has anyone actually looked at the CDi equation?

AR -> infinity means no induced drag. Think of it this way. The entire culmination of vorticity is accumulated and then shed at the wingtip. With a wall there, high pressure region cannot escape to the low pressure region.

[trinidefender]

I may have stepped in here at an inopportune time, but has anyone actually looked at the CDi equation?

AR -> infinity means no induced drag. Think of it this way. The entire culmination of vorticity is accumulated and then shed at the wingtip. With a wall there, high pressure region cannot escape to the low pressure region.

It isn't that you stepped in at in at an inopportune time. It is that you didn't read the thread in its entirety, yes I know it is long. If you did and read the sources provided you will understand more. You seem to be stuck in the same trap that many others are in thinking that induced drag is only created at the wingtips.

Induced drag is all drag created in the production of lift. Drag created by the creation of wingtip vortices and spanwise flow around the wingtips and all that jazz is only part of the induced drag equation. Induced drag encompasses far more than just drag created at the wingtips.

Please don't get stuck in that trap.

[turbof1]

turbof1 read the sentence above the formula that I quoted. "base drag coefficient at zero lift Cdo" therefore Cdo is all drag created that isn't created in the production of lift, or in Formula 1's case, downforce.

Yes, I got that. I just want to make sure this doesn't include induced drag anymore, but since induced drag is 'induced' by lift, Cdo is just a sum of all kinds of other types of drag.

What I think you are asking is. Is there a formula you can use to find the lift and drag forces FOR A DEFINED SECTION of an infinite wingspan wing? Is that what you are asking? If so, then no I do not have a formula for that. Pierce might.

Yes I am.

[trinidefender]

This is for finite wings but applies to what we are talking about, not the infinite wingspan part, and explains a lot about drag, induced drag, lift vectors, vortices, various laws and theories used in aerodynamics and their respective equations. Give it a read guys and girls.

http://www.tongji.edu.cn/~zyjin/aerodyn ... apter5.pdf

[NoDivergence]

This is for finite wings but applies to what we are talking about, not the infinite wingspan part, and explains a lot about drag, induced drag, lift vectors, vortices, various laws and theories used in aerodynamics and their respective equations. Give it a read guys and girls.

http://www.tongji.edu.cn/~zyjin/aerodyn ... apter5.pdf

You're not getting it. By definition, induced drag can only be determined for a finite wing. When you conduct vortex lattice method, you have two trailing vortices and a bound vortex in between to make a horseshoe vortex for each panel, and the span must be FINITE.

With infinite aspect ratio, you are talking about aerodynamics that relates to a 2D airfoil. You do not get downwash without a finite wing. I mean jeez, even the source you cite here (which I have read several years ago), mentions that downwash w is from wingtip trailing vortices (and the resultant downwash between them and upwash on the outside of them). This downwash is what changes the effective angle of attack, giving the force vector of induced drag.

Look at Prandtl's classical lifting line eq. Guess what happens when b goes to infinity? w goes to 0.

Sure, you can get a sectional lift from a rho Vinf gamma(y0), but to get lift for a wing you need to integrate across the span.

[turbof1]

I think that's the keypoint - equations for infinite wingspan aren't meant to calculate induced drag, but I believe how induced drag behaves. It gives a completely wrong impression. It has been said already by trindefender: it's simply impossible to get a correct understanding of induced drag towards infinity. That should be the main concclusion.

[trinidefender]

This is for finite wings but applies to what we are talking about, not the infinite wingspan part, and explains a lot about drag, induced drag, lift vectors, vortices, various laws and theories used in aerodynamics and their respective equations. Give it a read guys and girls.

http://www.tongji.edu.cn/~zyjin/aerodyn ... apter5.pdf

You're not getting it. By definition, induced drag can only be determined for a finite wing. When you conduct vortex lattice method, you have two trailing vortices and a bound vortex in between to make a horseshoe vortex for each panel, and the span must be FINITE.

With infinite aspect ratio, you are talking about aerodynamics that relates to a 2D airfoil. You do not get downwash without a finite wing. I mean jeez, even the source you cite here (which I have read several years ago), mentions that downwash w is from wingtip trailing vortices (and the resultant downwash between them and upwash on the outside of them). This downwash is what changes the effective angle of attack, giving the force vector of induced drag.

Look at Prandtl's classical lifting line eq. Guess what happens when b goes to infinity? w goes to 0.

Sure, you can get a sectional lift from a rho Vinf gamma(y0), but to get lift for a wing you need to integrate across the span.

Some downwash is from a wingtip. If have a flat wing set at an angle to the airflow it will change the direction of the airflow. Is this change in direction not downwash? While you aren't really incorrect in a lot of what you say, the fact remains that we have gone into the realm of theoretical physics. I have been trying to bring this thread back on topic of induced drag and how it relates to real wings.