Reducing the drag of a two element wing through stall

[kilcoo316]

Kilcoo, its not the leading edge of the flap, its the trailing edge. How it works is that the trailing edge is made thin and hence its chances of flexing increases.

By closing the slot size, the amount of energy being transfered reduces and stall occurs which results in an enourmous amount of drag! Hence its not acceptable.

But there is virtually no loading at the trailing edge, virtually all the pressure differential is on front half of the aerofoil. Besides, a composite wing can be set up in virtually any way the teams want.


Normally, I would agree, stalling is not acceptable, and is to be avoided at all costs. But when your aerofoil is mounted at 60-70 degrees to the flow, thus the component acting backwards is 85-95% of the 'lift' [as the wing sees it] there may be benefits to producing less 'lift'.

[miqi23]

Kilcoo, firstly the flap is not set at an angle of 60 to 70 degrees. Yes the trailing edge cause the flex since the pressure distribution on the flap does not have peaks and is rather ideal.

35 to 40 degrees is prefered when it comes to flap angle having a certein Camber and thickness value

[Reca]

Reca, are those just generic aerofoil sections or did you get them from somewhere?

The airfoils are Benzing airfoils from the Benzing’s book I mentioned in the other thread. I made the diagram from an old image of the section of a 3d model I made months ago and then modified it in photoshop to close the gap. I changed the airfoils of the 3d model since then so I don’t remember which ones I used at the time. I can look in the old files to see if I discover it, but consider that it was a basically random choice, for the airfoils, the relative size and the relative positions.
Meanwhile you can look http://www.benzing.it/enrico.profili.htm there are a few airfoils there that you can use if you are interested in making CFD on a model.

[NickT]

Ok guys and girls, I am playing Devils Advocate here and thinking outside the box

The flexible wings are nothing to do with drag reduction, they are to do with deliberate down force reduction

In general terms downforce increases with speed. With really high levels of down force you need to run a very stiff suspension to maintain ride height and prevent bottoming. However, this minimises suspension complience, particularly in low and medium speed corners.

If you maximise your low to medium speed downforce generation and prevent excessive downforce at high speed it will allow you to run a softer and more complient suspension. This will give you an advantage in braking, acceleration, over the curbs and bumps.

[manchild]

downforce reduction = drag reduction (if wing flexes so that its attack angle decreases)

[kilcoo316]

Kilcoo, firstly the flap is not set at an angle of 60 to 70 degrees. Yes the trailing edge cause the flex since the pressure distribution on the flap does not have peaks and is rather ideal.

35 to 40 degrees is prefered when it comes to flap angle having a certein Camber and thickness value

I've a high res pic of the F2001 here in front of me, and the rear wing 2nd element chordline is at more than 60 degrees easily.


http://naca.central.cranfield.ac.uk/rep ... rt-614.pdf

From here, you can see that before the flap stalls there is the normal pressure distribution over the 2nd element, i.e. mostly ahead of the 1/4 chord point.


The reason for the stall in this case is due to the relatively uncambered nature of both 1st and 2nd element aerofoils.

[Tp]

I'm unsure what would be advantageous about stalling the upper element. When I thought stalling was something to be avoided.

The way I see it is, the gap between the upper and lower element decreases, so the disruption of airflow drecreases, so the drag decreases.

[mini696]

...they are to do with deliberate down force reduction.

Redusing downforce also decreases power loss due to friction (in a straight line as well as corners). Therefore a flex wing will increase top end because of reduced aero AND mechanical drag.

Cool huh!!

[miqi23]

Kilcoo, firstly the flap is not set at an angle of 60 to 70 degrees. Yes the trailing edge cause the flex since the pressure distribution on the flap does not have peaks and is rather ideal.

35 to 40 degrees is prefered when it comes to flap angle having a certein Camber and thickness value

I've a high res pic of the F2001 here in front of me, and the rear wing 2nd element chordline is at more than 60 degrees easily.


http://naca.central.cranfield.ac.uk/rep ... rt-614.pdf

From here, you can see that before the flap stalls there is the normal pressure distribution over the 2nd element, i.e. mostly ahead of the 1/4 chord point.


The reason for the stall in this case is due to the relatively uncambered nature of both 1st and 2nd element aerofoils.

The paper you have here makes use of NACA aerofoil sections. As I said, 40 degrees the most and if you add CAMBER to it, trust me it looks lilke 60 degrees. I will upload some wing designs in a while and then ask your self at what degrees are they set to! They are at 40 degrees but looks more than that due to Camber. Obviously, the basic rules of aeronautics apply but the whole story is totally different.

Furthermore, I will also show you some screen shots of the same wing performing in isolation and with close proximity to the car! Just see how things change!!! Yeah, the analysis in the paper are done in 2D and not 3D. There is a whole world of difference between 3D and 2D and most importantly the separation point of the flow. Again more coming on this later!

[kilcoo316]

I'm looking at my rear wing pic again... and there really is no way its chordline is at less than 60. I'll email it on to you.


Yeah, 3D will stay attached for slightly longer due to the trailing vortex system.


Can't wait for the screenshots

[miqi23]

I'm looking at my rear wing pic again... and there really is no way its chordline is at less than 60. I'll email it on to you.


Yeah, 3D will stay attached for slightly longer due to the trailing vortex system.


Can't wait for the screenshots

Have a look at the following image, a 2D analysis. Note the separation point at the trailing edge of the main element. The second image is of the same wing analysed in 3D. Notice the oilflow profile on the lower surfaces this time. Its attached all the way on the main element, however separates on the flap. Both are totally the opposite.

[IMG:800:711]http://img367.imageshack.us/img367/1299/be5fp.jpg[/img]

I should post some more as promised of the 3D wing on car and guess what! the flow separation on the flap due to the upwash produced by the diffuser disappears. In summary, the rear wing and the diffuser feed each other!

[IMG:1209:711]http://img476.imageshack.us/img476/9900 ... cal9pi.jpg[/img]

As far as the angle of attack is concerned, I dont look at the chord length as means of measurement since at 90 degrees the lower surface is still below 90 degrees. The images you are seeing are at 40 degrees and looks 60! Yeps you are correct if you take the chord as the means of measurement.

[zac510]

Great pictures miqi, you are certainly MVP this month

[bazanaius]

Hey guys, I am just thinking about stall on F1 wings. I know that the stall of a wing is used in a wide variety of situations on an F1 car, but I was wondering if someone could talk through the different occasions when you'd want it, what it achieves and a brief description of how you might achieve it?

e.g. I know that some diffusers are designed to stall at high speed, decreasing drag when high down force isn't required - is this just setting the exit angle at the appropriate incidence to stall at a desired speed?

Also, I've heard of front wings stalling on braking into a corner - how would this sudden loss of down force help? Is this achieved in a dynamic sense - braking shifts weight forward, momentarily increasing incidence and stalling the wing?

so,yeah - what applications to stall by design have in an F1 car? discuss...

Baz

[Giblet]

I think you would want any wings to stall at a certain speed, since the less wing on the straights the better.

I think the stalling into corners you talk about is more because of the slower speed, and the lateral motion of the car moving air across the wings.

The other way to acheive stall is not keep your revs up before leaving the pits

[fastback33]

Hmm.. Interesting idea, i've never heard of this. How is it achieved?