Mclaren Mercedes MP4-25

[ringo]

It is definitely a stalling mechanism. Yes, this will decrease the effectiveness of the diffuser but at 300kph down a straight you don't really care about the absolute downforce level you are producing - as long as you can shed 10-15 pts of Cd.

And yes, it is driver operated. Somehow.

You're free to believe this, just like some people believe in the 2nd coming.

However, you have to appreciate that the rear wing and diffusor work in conjunction with each other.
Higher efficiency of the rear wing increase the scavenging of the diffusor which increase downforce.
remove the rear wing and the diffusor alone does not keep the car on the ground nor does it maintain stability. If it did then when a rear wing falls off, the car would go faster and still be stable. However we see in reality that when a rear wing falls off, the car looses stability.

The wing difuser relationship is complicated, but the diffuser will still create downforce without the wing, just not as much. Removed wing is more related to the back of the car lifting and upseting the aerodynamic balance, taking away upwash from the diffuser, and also increasing rideheight which affects the diffuser again.

If you stall the rear wing, its the same effect as removing the wing.

Not really, remember the object will still be there creating massive amounts of drag.
So it is a lose-lose situation. Not the same as no wing at all.

Maintaining equal pressure on both upper and lower surfaces of the wing is not possible unless you can blow a very large VOLUME of air into the wake behind the wing. You cannot achieve that without a large pump pumping slowly. So the only way to stall the wing is too use the engine as a pump, robbing power.

No, infact it may require no power at all. If you shoot a hole through a plane wing the pressure will equalize and the plane will drop out of the air. No power required!

The purpose of the flap blowing has nothing to do with stall. get over it, its science fiction.

True, but SLC is not reffering to flap blowing.

Flap blowing is about wing efficiency through boundary layer control.

It's also about relative speed control.

i know we love to get the creative juices flowing so lets talk about magnetic levitation for the MP4/25 or how about turning it into a hover craft down the straight with all the stalled air in the now choked (if you believe in wing stall) diffusor. Lets discuss some stability control mechanisms to make this work.

Stalled wings is nonsense, can we move on...

Moving on now, to not stalling the wing.

Just for simplicity, this is not exactly what is happening, but is a basic representation for clarity.

The longer arrows indicate greater pressure.
Pressure difference results in a force on wing in the direction of the greater force, or drag force. Newton's second law basically.
The lower pressure underneath is where the suction comes from to create the down-force. The suction is the most sensitive side and makes a bigger contribution than the high pressure side to the down-force.

The only way to reduce drag, maybe even more than non powered flap blowing can compensate for, in this case, is to reduce the pressure difference. This is simple achieved by making a "hole" between both sides of the wing or introducing higher pressure on the back side.

Here the pressure on the back side is being increased by introducing free stream air. This when coupled with the pressure on the front, will result in a smaller net force, thus less drag. Subsequently the lift force will be reduced because of the reduced suction under the wing.
The difference here between stalling is that the wing can behave like it wasn't there to begin with, since there is no separation. It's technically stalling the wing in a sense that it is not lifting, but it does not have the other drawbacks associated with stalling.

I think this is what SCL was alluding to, and it makes sense.

[Just_a_fan]

yep, seems to me that my idea is true (which it probably isn't) then you'd tune it for the track; so the wing stalled at slightly faster than you'd take the fastest high speed corner.

But how would you tune it taking account of the ambient wind speed? A 20kph wind blowing across the circuit would mean that you'd need to tune the device to allow for a 20kph head wind and a 20kph tail wind (a 40kph difference or about 15-20% of the car's speed in a high speed corner). That would be impossible to do. And you'd need a "gust margin" too in case the 20kph wind gusted to, say, 30kph briefly just as you were mid-corner. Stalling the rear wing mid way through a 250kph corner would be, um, interesting for the driver.

[cupidstunt]

yep, seems to me that my idea is true (which it probably isn't) then you'd tune it for the track; so the wing stalled at slightly faster than you'd take the fastest high speed corner.

But how would you tune it taking account of the ambient wind speed? A 20kph wind blowing across the circuit would mean that you'd need to tune the device to allow for a 20kph head wind and a 20kph tail wind (a 40kph difference or about 15-20% of the car's speed in a high speed corner). That would be impossible to do. And you'd need a "gust margin" too in case the 20kph wind gusted to, say, 30kph briefly just as you were mid-corner. Stalling the rear wing mid way through a 250kph corner would be, um, interesting for the driver.

I think we've fairly well established that there is no intent to stall anything.

Ringo I like your diagrams.... this all seems to be pretty similar to the effect a bendy wing would have. Progressively less downforce and drag at high speed (when I say less I mean less of an increase).

[SLC]

I think we've fairly well established that there is no intent to stall anything.

This is not in any way well established. Why do you think there was such a big hoo-ha about flexible wing elements and closing up of slot gaps in 2005-2006? Because they stalled the rear wing.

The rear wing produces a fair amount of downforce, and a fair amount of drag. Without getting into any semantics regarding pressure drag, induced drag or whatever, just look at the sections of a typical F1 top rear wing - the average camber line is extremely angled (practically vertical).

The total load vector of the wing assembly has a significant horizontal component - this, in its simplest form, would be called pressure drag.

If you stall the wing the load vector reduces in magnitude by a relatively large amount - and obviously therefore the horizontal component of this vector (the pressure drag!) is massively reduced.

Yes you lose downforce, but nobody gives a crap about downforce at 300kph down a straight. Drag reduction is golden.

This is not something that can be argued - it is a fact. I'll repeat it in case someone missed it. Stalling the top rear wing of an F1 car reduces the car's total drag. This is not the case for a relatively lightly loaded aircraft wing in steady level flight, before someone digs up some random paper on it.

Rumour has it McLaren are using some sort of pressure sensitive circuit (google "fluidic switch") within the roll hoop to control the mass flow down the engine cover duct - it can be extremely precise in its velocity switching effect, and that the mechanism can be controlled (but obviously not in any active or electronic way - this would be very illegal) via the driver's leg or knee.

[SLC]

Sorry for posting twice in a row, but I thought it was worth mentioning the following.

The effect that McLaren have implemented with the 2010 RW is the opposite effect of the second slot gap they ran with at high downforce circuits last year (as well as BMW).

Last year they used the Y75 legality loophole in the centre of the wing element to put in a duct in the top of the mainplane - and through clever interpretation of the "number of sections" rules in the top rear wing box effectively designed a three element wing (triplane).

This was specifically such that they could push the wing harder without it stalling.

This year they have designed a system to stall the wing on purpose.

Also, whilst we are on the rumour front, this stalling system has apparently been in the works for the past three years...

[ringo]

For the blown flap theorists, i want to go into the actual details here.

Now the arguement is:

that the angle of attack can be increased even more, without stalling, for more DF

Or the angle of attack can be reduced, and flap blowing can compensate and regain the DF while having less drag.


Blown flaps are always powered by some device. In the case of the Mp4, the blown jet is not powered at all.

My question is, where is the power to blow the jet coming from?
It cannot be any ram effect from the fin, because the blown jet has to be much faster than the air under the wing.
The flow under the wing can be around 3 times the free stream velocity or more. What in the fin could be driving the air by that much?
That is where i am doubting the blown flap.

[ringo]

Sorry for posting twice in a row, but I thought it was worth mentioning the following.

The effect that McLaren have implemented with the 2010 RW is the opposite effect of the second slot gap they ran with at high downforce circuits last year (as well as BMW).

Last year they used the Y75 legality loophole in the centre of the wing element to put in a duct in the top of the mainplane - and through clever interpretation of the "number of sections" rules in the top rear wing box effectively designed a three element wing (triplane).

This was specifically such that they could push the wing harder without it stalling.

This year they have designed a system to stall the wing on purpose.

Also, whilst we are on the rumour front, this stalling system has apparently been in the works for the past three years...

Your onto something. I guess we have pretty similar ideas, just a difference of wording.

[kalinka]

Raptor22, I agree with you completely. You described our situation very well !

Pup, thanks, I was misunderstooding you.

SLC, As I can remember, the flexible wings concept was that the pressure that presses the wing downward actually decreases the wing's angle so that the wing at high speed acts like a wing with much smaller angle-->smaller drag. And I think it's the only way they are reducing drag, not some other effect.
This is what I found on F1fanatic.co.uk :

"Flexi-wings in theory

Flexible wings both front and rear have fallen foul of the rule books on more than one occasion, but the basic principle behind them has always been the same.

Aerodynamic wings only generate downforce above a certain speed. Once that speed is exceeded the wings generate both downforce (which pushes the tyres into the ground, improving grip) and drag (which slows the car).

Ideally designers would build movable wings that can have a deep profile when the car needs cornering grip and a shallow profile when the car is flat-out down a straight and needs minimum drag. But according to the rules, wings are not allowed to move relative to the sprung part of the car.

Flexi-wings are an attempt to get around that rule by letting the wings change shape (i.e. flex) of their own accord by using less stiff materials in certain places."

I didn't found any evidence around, that the felxwings have any to do with some "stall"effect.

[Pup]

Rumour has it McLaren are using some sort of pressure sensitive circuit (google "fluidic switch") within the roll hoop to control the mass flow down the engine cover duct - it can be extremely precise in its velocity switching effect, and that the mechanism can be controlled (but obviously not in any active or electronic way - this would be very illegal) via the driver's leg or knee.

The only place I've seen this is in your posts. It would be nice to know where you're reading this info, so we could see the entire conversation. This is a pretty serious accusation to be making without providing any evidence.

Also, and this doesn't just apply to you, you guys really need to go back and look at the posts from Jan 31 and Feb 1, because there's been absolutely nothing posted today that wasn't talked about at end when all this first came up. That includes the whole made to stall vs. made to not stall discussion, tuning the stall point for different tracks, etc.

It's then been discussed at least once a week since as new people have joined the conversation. Sorry guys, but it's just getting to be a bit of a pain.

[horse]

If you stall the wing the load vector reduces in magnitude by a relatively large amount - and obviously therefore the horizontal component of this vector (the pressure drag!) is massively reduced.

ONE BIG EDIT:

Hi SLC, could you explain the physics of this a little more for me? I'm finding it a bit counter intuitive. My understanding was that pressure drag is caused by the flow about the aerofoil separating and therefore the slot will just increase this phenomenon, no? I get the idea of trying to remove the element where downforce is not required, but I don't see how this system could physically do that without increasing the drag.

Also, and this doesn't just apply to you, you guys really need to go back and look at the posts from Jan 31 and Feb 1, because there's been absolutely nothing posted today that wasn't talked about at end when all this first came up. That includes the whole made to stall vs. made to not stall discussion, tuning the stall point for different tracks, etc.

It's then been discussed at least once a week since as new people have joined the conversation. Sorry guys, but it's just getting to be a bit of a pain.

Sorry, Pup, I didn't believe it first time around, and I suppose I still don't and am waiting for a convincing explanation of the stall phenomena which would not cause extra drag. Anyway, I'm going to have another look through.

EDITx: This is my feeling for it, if you disrupt the normal airflow on the left by injecting airflow on the right, you actually make the drag worse by redirecting the vector more in the plain of motion of the car.



Ok, you lose some of the DF vector acting in the wrong direction too, but I can't see this system being all gain and no loss. I guess the multi-element wing is a tad more complicated than this too. I think the assumption is that injecting into the suction side, would not disrupt the airflow about the wing, and that's where I would contest it unless you're energising the boundary layer to avoid separation.



Here, you'll get a vortex sheet formed between the injecting fluid and the free stream fluid, no?

[kalinka]

For the blown flap theorists, i want to go into the actual details here.

Now the arguement is:

that the angle of attack can be increased even more, without stalling, for more DF

Or the angle of attack can be reduced, and flap blowing can compensate and regain the DF while having less drag.

Both

Blown flaps are always powered by some device. In the case of the Mp4, the blown jet is not powered at all.

1. It's powered by sucking in air at airbox ( upper slot ,we see some covering experiments on tests) and blowing it out on the rear wing's small holes/slit trough shark fin. Evidence : not completely flat shark fin at the rear wing, but somewhat bulky, and above mentioned dual intake on airbox + hardly visible horisontal line on the back of RW.

2. It may be powered by cooling exhaust gases, but that highly unlikely like Raptor22 mentioned.

My question is, where is the power to blow the jet coming from?
It cannot be any ram effect from the fin, because the blown jet has to be much faster than the air under the wing.

I didn't found any evidence trough my study of this effect that the blown jet must be much faster than airflow. But the amount of air must be enough, and that's the point where it can fumble, but I think it's impossible to tell from here can it be enough or no in case of MP4/25

The flow under the wing can be around 3 times the free stream velocity or more. What in the fin could be driving the air by that much?

It's not the blown in air that creates the downforce. It creates only the boundary layer that helps the large amount of faster air coming from the leading edge, to stay attached to wing, as I understand this effect.

That is where i am doubting the blown flap.

That's what I learned trough many many hours of "investigating" blown wings, but for sure I'm not an expert of these. It's only my conclusion from many sources. You can find some in my previous posts as well.

[kalinka]

OK, I agree Pup, we should end this blown/not blown/stall thing. We know
too little about the MP4/25 design to go further. It'll be just iteration of things. We may see/not see later during the season who was wrong/right.
Let's find another detail on MP4/25 to discuss. There's plenty of it

[ringo]

@horse

Vortex is usually formed on the ends of the wing, where the high pressure meets the low causing circulation. End plates stop the top side flow from meeting with the bottom side flow too.
I cannot really say what happens when the air is injected through that slit though because i have never seen it before. I just think the idea is feasible.


This thread is going to be bigger than the UsF1 thread before the first race. Imagine if the car gets an updated part

[cornermarker]

First time posting, and let me tell you, innovation is why I love F1. I'm gonna need some help from the more scientifically minded, especially those who understand fluid dynamics and pressure gradients, etc. Sorry this is so long, I don’t have a blog, otherwise I would have posted there.

Is it possible that the engine cover and fin of the MP4-25 contain two pressure chambers, utilizing pressure gradients between the two to determine whether the slot sucks or blows? The slot, of course, is accessed by a tube to the higher chamber. Someone posted this link http://www.aerolab.com/Display_Pages/Flow_Vis.html which finally convinced me that both were possible.

I started with the car. Outwardly, the car appears to be built for outright pace. Long wheelbase, tiny sidepods, beautiful scupting. It's a rocket. Where it would need help is in the low speed, twisty bits. So I believe the focus is on increasing df at low speeds, by further lowering the pressure behind the wing, using suction. But, as it turns out, it might be very simple to also do the opposite: slightly increase the pressure behind the wing at high speeds (reducing downforce, and therefor drag) by blowing.

So, you would achieve suction only by making the pressure in the upper chamber lower than the pressure at the back of the wing at the desired speed (let’s say 60mph). You’d start with the known quantities, such as likely pressure at the back of the wing at an average track, at 60. Also, average amount of pressure in the lower chamber in the same conditions. From those knowns, you would build a chamber of the proper volume and shape in the fin that would, in these conditions, be at lower pressure than the rear of the wing, higher pressure than the lower chamber (the black duct?). You would do so using the upper intake slot, and the venturi effect, created by a body of air moving in the lower chamber that is, perhaps, heated and accelerated by a hot oil cooler.

So then, how is the sucking stopped at higher speed and even reversed to raise the pressure of the air behind the wing, and done *passively*? This time you’d need the pressure of the upper chamber to be higher than that behind the wing, and this would be relatively easy to achieve, as the pressure behind the wing is very low at high speed. Perhaps the greater amount of air to the upper slot is alone enough to increase the pressure, or perhaps the oil cooler, cooled by greater supply of ambient air at high speed, transfers much less heat to the lower chamber. Denser, cooler air in the lower chamber means it doesn't move as fast as it might, and the venturi effect increases at a disproportionately lower rate than the increase in pressure in the upper chamber. The pressure rises in the upper chamber to the point where it’s higher than the rear of the wing, and as a result air is released through the slot.

So, It’s possible the slot in the rear of the wing is there only to gently blow at hight speed, and gently suck at low speed. No dramatic changes, just for slightly increasing or decreasing the pressure gradient, front/back of the wing. Not a race winner, just a little help at speed extremes. The season’s not over if it fails, simply close off a valve in the duct to the slot.

Could this work?

Questions:

Does moving air in a regular pipe actually speed up when it encounters a heated section?

How important to the venturi effect is the difference in temperature when talking about two volumes of air at very different pressures?

How tightly fitted and sealed is the body work. Is it possible the whole lower engine cover + sidepods make up the lower chamber? This could be the cause of the appearance of “bleeders” above sidepods, and vents elsewhere. Not to control temp, but pressure. I believe they appear in the same pictures, would be interesting to know if these were taken on cold days (dense air).

Would an electronic or hydraulic switch (for controlling the temp. of the lower chamber) be a problem with the FIA?

Kelpster

[Pup]

I think for a vacuum wing to work, you have to have several slots along the surface of the wing, like in the example shown in the link. So I'm doubting that the single slot would do the trick.