Reducing the drag of a two element wing through stall

[outer_bongolia]

I think I am learning slower than many here.. But I was just thinking of the angles of the two main components of the rear wings..

The bottom element can work like an upside down plane wing, creating a decent amount of downforce from the lift in addition to changing direction of the flow. But if the top element is not stalled, the lift (again talking in airplane wing terms) will be actually kind of backwards at a steep angle. This force will provide some downforce, but will also create a force pulling the car backwards (figuratively speaking). So, the best thing to do with the top element would be actually stalling it. That would kill the lift on that wing. The main contribution to the downforce would come from the change in the direction of airflow above the wing.

My ignorant theory is as follows - feel free to correct:
There were many links to the theory of the blown wing. As far as I can summarize it helps prevent the flow separation and keeps the laminar flow around the wing, enabling it to work at higher angle of attack without stalling. In the upper element of the rear wing of the Macca it should work best when the car is going relatively slow would actually further slow it down while generating some extra downforce. So, if the snorkel is somehow controlling the airflow and is connected to the driver's left foot, it might be actually allowing the flow during braking as an aid to slow the car more efficiently.

It would be easy to tie something to the brake pedal that opens a valve instead of expecting the driver to try to squeeze a tube with his knee on the straights.

No need for flame, just point out that this is dumb or has been explained (in a way I couldn't understand) before.

[timbo]

Here's scarbs' idea http://scarbsf1.wordpress.com/2010/02/2 ... el-rumour/

[SLC]

The bottom element can work like an upside down plane wing, creating a decent amount of downforce from the lift in addition to changing direction of the flow. But if the top element is not stalled, the lift (again talking in airplane wing terms) will be actually kind of backwards at a steep angle. This force will provide some downforce, but will also create a force pulling the car backwards (figuratively speaking). So, the best thing to do with the top element would be actually stalling it. That would kill the lift on that wing. The main contribution to the downforce would come from the change in the direction of airflow above the wing.

This is pretty much correct.

It's all about the resultant force vector of the wing and how that changes as it stalls.

Everyone who is quoting Cl v Cd and talking about angle of attack - yes, a traditional single element aerofoil section will see an increase in drag when it stalls. But we are talking about an extreme high lift two element wing - the flow mechanics around this is different.

[tok-tokkie]

Here's scarbs' idea http://scarbsf1.wordpress.com/2010/02/2 ... el-rumour/

I find that really amusing. I was the first to propose the idea that it was linked to the 'stalling' duct. I did it to illustrate some of the crazy ideas and alternative (imaginary) aerodynamic laws that were being proposed in that discussion. Now it seems it actually may be true. Many a true word said in jest?

[horse]

But we are talking about an extreme high lift two element wing - the flow mechanics around this is different.

This is the part of the issue for which I haven't been able to get a good answer from anyone yet. It looked to me, that in slimjims simulations all the work was being done by the main element, so it seems feasible that stalling the flap to reduce the DF of the main element might be beneficial. Again, I've been up all night so I might be raving.

The control mechanism still seems bizarre though. What if the driver has to move his leg unexpectedly?

[hollus]

Indeed the knee squeeze would be a bizarre control mechanism, but a safe one. One would not squeeze it by mistake, I guess, and if for some reason the driver moves his leg and stops squeezing in a straight, he suddenly gets more drag and downforce, the car accelerates a little less and he has lost half a tenth of a second. Safe.
Now, it looks dubious that enough air can get through that snorkel and through a couple of meters of tubing to feed enough fast air to the blown slot. Some people have suggested that the tube would not directly provide the flow, but pressure to activate a valve somewhere. Wouldn't that be a mobile aerodynamic device again?

Wow, we are not sure that the shark fin is feeding anything, we are not sure that the slot is really there or if it is blown or meant for suction or just passive. We don't know what the snorkels are for and for sure nobody has seen any tubes. But with so many unusual things in the Macca, I hope come Bahrain somebody will challenge its legality. Then we might know.

[biggles22]

But we are talking about an extreme high lift two element wing - the flow mechanics around this is different.

This is the part of the issue for which I haven't been able to get a good answer from anyone yet. It looked to me, that in slimjims simulations all the work was being done by the main element, so it seems feasible that stalling the flap to reduce the DF of the main element might be beneficial. Again, I've been up all night so I might be raving.

The control mechanism still seems bizarre though. What if the driver has to move his leg unexpectedly?

slimjim's simulations show that when the wing is blown drag is REDUCED and downforce is INCREASED. So the car is more stable, both on straights and in corner's, but also have less drag so will have a higher top speed.

The rest of my comment isn't aimed at you, just a general rant...

It's fairly obvious that the top air intake above the driver's head is fed toward to the rear wing, why would you use the bottom engine intake for it when the top one is there and separate. The slit in the upper element of the rear wing is tangential to the point on the curve, if you look on pictures it's quite obvious, pictures taken from higher up or a higher angle show the slit to be much darker and wider, whereas lower pictures show a faint thin line, even to the point where the slit can't be seen.

The flow could easily be increased to faster than air speed round the car. The size of the intake, for arguments sake, is around 0.1m by 0.05m, so the area is 0.005m^2. the slot on the rear wing is 0.8m long and, again for arguments sake, is 0.003m (3mm), so the area of the slit is 0.0024m^2. That's just under half the area of the upper air intake, therefore ignoring frictional loses and any work done on the air the air speed would be twice as fast, then same air speed's as slimjim used in his simulations.

For a blown wing like this I see no reason for needing driver control of this effect. At lowspeed the flow will always stay attached so downforce and drag will be the same as a normal unblown wing because at these low speeds the flow doesn't separate. When the speeds are increased the flow will stay attached due to the blown slot, drag will DECREASE and downforce will INCREASE, in accordance with slimjim's simulations.

I can't see why it is so hard to believe in this effect?

Although the point in this thread is to conclude whether stalling a wing is effective or even desired, I think people shouldn't consider McLaren's rear wing to be one that is being stalled when all the facts, simulations and pictures point at it being blown.

By the way, I am no professional, just an A level student who strongly follows F1 and have raced in motorsport for a lot of my short life. I feel this solution is common sense, people are digging too deeply for complex solutions, Occam's razor springs to mind.

[astracrazy]

i fail to see how scarbs idea with the drivers leg works? what if the driver needs downforce round a fast corner but doesn't need to break for it? like turkey turn 8 perhaps?

[Raptor22]

Here's scarbs' idea http://scarbsf1.wordpress.com/2010/02/2 ... el-rumour/

I think Scarbs lifted that fantasy from the F1technical forum...

This rumour should be renamed to McLaren MP4/25 Bagpipe car.

[ringo]

That thing is a cooling duct.

Why need a pressure switch when they can install a more well hidden and direct switch like a button, a third pedal, or if the knee is to be used a button on the side wall of the tub or if they are really desperate to hide it, a buttocks switch that senses pressure when squeezed?
Even the very same pitot tube on the front of the nose can be used!
There is no reason for a passive control system to be sensitive to air speed, when it loses all that sensitivity to a fumbling sweaty knee blocking a hole.
We may see Button and Lewis with suction pads on their knees before the hop into the car.

[ringo]

It is being blown, but it can be blown to be stalled, that is what some of us are saying.

[TheMinister]

It is being blown, but it can be blown to be stalled, that is what some of us are saying.

Others (me) think that the blowing prevents it from stalling, so stopping/reducing the blowing at high speeds will cause it to stall.

[biggles22]

It is being blown, but it can be blown to be stalled, that is what some of us are saying.

By blowing tangentially from the wing against the flow, or by blowing normal to the wing?

I would disagree and refer back to my point about how the slit is more noticeable from a higher angle, which would be say it is being blown upwards, counter flow would be less visible from a higher angle and more more visible from a lower angle, which is the opposite yo what we can see. Normal to the wing blowing would be highly visible from the majority of angles we have seen, but the facts are it isn't, from lower camera angles the slot is nearly invisible.

[ringo]

But we are talking about an extreme high lift two element wing - the flow mechanics around this is different.

This is the part of the issue for which I haven't been able to get a good answer from anyone yet. It looked to me, that in slimjims simulations all the work was being done by the main element, so it seems feasible that stalling the flap to reduce the DF of the main element might be beneficial. Again, I've been up all night so I might be raving.

The control mechanism still seems bizarre though. What if the driver has to move his leg unexpectedly?

slimjim's simulations show that when the wing is blown drag is REDUCED and downforce is INCREASED. So the car is more stable, both on straights and in corner's, but also have less drag so will have a higher top speed.

The rest of my comment isn't aimed at you, just a general rant...

It's fairly obvious that the top air intake above the driver's head is fed toward to the rear wing, why would you use the bottom engine intake for it when the top one is there and separate. The slit in the upper element of the rear wing is tangential to the point on the curve, if you look on pictures it's quite obvious, pictures taken from higher up or a higher angle show the slit to be much darker and wider, whereas lower pictures show a faint thin line, even to the point where the slit can't be seen.

The flow could easily be increased to faster than air speed round the car. The size of the intake, for arguments sake, is around 0.1m by 0.05m, so the area is 0.005m^2. the slot on the rear wing is 0.8m long and, again for arguments sake, is 0.003m (3mm), so the area of the slit is 0.0024m^2. That's just under half the area of the upper air intake, therefore ignoring frictional loses and any work done on the air the air speed would be twice as fast, then same air speed's as slimjim used in his simulations.

For a blown wing like this I see no reason for needing driver control of this effect. At lowspeed the flow will always stay attached so downforce and drag will be the same as a normal unblown wing because at these low speeds the flow doesn't separate. When the speeds are increased the flow will stay attached due to the blown slot, drag will DECREASE and downforce will INCREASE, in accordance with slimjim's simulations.

I can't see why it is so hard to believe in this effect?

Although the point in this thread is to conclude whether stalling a wing is effective or even desired, I think people shouldn't consider McLaren's rear wing to be one that is being stalled when all the facts, simulations and pictures point at it being blown.

By the way, I am no professional, just an A level student who strongly follows F1 and have raced in motorsport for a lot of my short life. I feel this solution is common sense, people are digging too deeply for complex solutions, Occam's razor springs to mind.

so you are saying that if the car is moving at 200mph, the jet will be blowing at 400mph?
Using Bernoulli equation the pressure drops, but that flow wont leave the wing if it's pressure is lower than what is outside of the slit. You get a case of back pressure since you are reducing from atmospheric with a velocity head to something much lower because you accelerate the flow.

This is why most blown wing in practice are fed by bleeding from the engines compressor, which has pressures way way above atmospheric. Another reason why i don't think this thing will blow much faster than free stream, or i should say it's outlet speed is dependent on whatever pressure is under the wing element.

This makes me thinking of making a fin instead of setting the slit velocity. It never ends.

[ringo]

It is being blown, but it can be blown to be stalled, that is what some of us are saying.

By blowing tangentially from the wing against the flow, or by blowing normal to the wing?

I would disagree and refer back to my point about how the slit is more noticeable from a higher angle, which would be say it is being blown upwards, counter flow would be less visible from a higher angle and more more visible from a lower angle, which is the opposite yo what we can see. Normal to the wing blowing would be highly visible from the majority of angles we have seen, but the facts are it isn't, from lower camera angles the slot is nearly invisible.

That is assuming it is being blown tangentially. We don't know, this is why i try to incorporate all the possibilities.