Reducing the drag of a two element wing through stall

[Shaddock]

Lets forget the snorkel and the knee thing for now.It's too clumsy.. and It's just silly. Imagine what's going to happen in those 3g corners. and there is no space for a rubber tube, or hollowed out section anyway.
No need to use the snorkel when you have a bigger extra hole under the air intake box.

I will soon post a pic of how i think it works using the fluidic valve idea.

Do you think the snorkel was a 'DIY' device because they couldn't quite get the aero internals to work in testing, and fitting a snorkel was just a proof of concept?

[ringo]

I am going to try and look on some numbers and rationalize this thing.

Now at barcelona the back straight top speed is 309kph or 85 m/s.
A 6kph increase , call that 87m/s.

Now the engine's power doesn't change, so it's going to take the same drag force to reach top speed. So the drag force is common to both cases.

Drag = 1/2 *density*V^2* Area* Coeficient of drag.

for both cases we can equate since drag is the same:

1/2*density* (85^2)*A*Cd1= 1/2*density*(87^2)*A*Cd2
Cd1= (87^2/85^2) Cd2

which means the new drag coefficient is 0.9545 times that of the normal car, assuming everyone's design is the same, and their using the same engine an car yadda yadda.

This is a small drop of 4.54% in total drag over the whole car. But considering that the wing is 1/4 of the total drag as well (could be way off) , and the drop is from the wing alone, then the wing itself has a drop of 4.54/0.25 = 18.16% in wing drag.

The upper element is about 35 to 40% of the total wing area, so comparing 40% to 18%, it can be said half the upper element is virtually deleted.

I think this is why they had they pitot array on the rear of the wing. If anyone was following this, it can make a little sense. The question is, what the hell did they do to get a little slot to drop the drag so much?

[volarchico]

SLC, is this diagram from simoncm what you have been describing? Once I saw this image, it made me think about what you've been saying and it sure made a whole lot more sense! But since you seem to be the closest one to the real issue and have the background, I want to make sure this is what you have really been describing.

Thanks! Sorry to come off sounding like an arse earlier.

[PlatinumZealot]

When I imagine the construction of the knee activator, with no moving or flexible parts, I can only see a solution with a hollowed out wall or some hollow duct in the side of the chassis with a hole in it.

The driver puts his knee over/in the hole to activate it (driver activated device). A problem is that the driver might not seal the hole properly with the side of his knee. Then again this depends on what you want to happen in the duct. If you want to stop air loss in the duct, then the drivers knee must seal the hole. If you want to decrease airflow in the duct the drivers knee only has to go inside the hole, into the ducting to block off most of the flow. Just some thoughts. Not saying it can not work even though it seems illegal anyway..but I think the air can be controlled without the driver and the weird ducting. (we still have to establish if the air int he duct is powerful enough to divert the bigger flow).

From scarbsf1


Imagine making a duct for this in the side of the chassis... I don't know.. I have to think hard on it.

[SLC]

Believe me, and I don't mean for this to sound egotistical, but C Horner, myself, and countless other people understand perfectly the physics of what is going on.

I'm surprised by that, chap, considering he doesn't have a degree. Has he found time to do that Open University course, now?

EDIT: I know, I know, this is a bad thing to say, I have no idea how good CH is at aerodynamics. I'm just a bit peeved at the insinuation that the opinions of other people here are less valid than your own SLC, because, frankly, I don't think that is true. There is, in the end, a fact about the operation of the McLaren wing and you seem to understand that fact well. However your explanation of the mechanisms leading to that fact have been very poor and left doubts in those that are not willing to simply believe what they are told. In addition, your audience is varied and doesn't necessarily understand the semantics of your discipline and, thus, this has also caused confusion.

PS What was your PhD about, by the way? May I read it?

My explanation is pretty clear, as far as I'm concerned. Did you see the crappy MS Paint job I did a couple of pages ago? I simply don't see how I can describe it any clearer than that.

You may not think it's true, and again, I don't mean to sound like an arse, but it is very clear that the opinions of many people on here are less valid (scratch that, they are often simply wrong and inappropriate) compared to people who genuinely understand whats going on (yes I know, that sentence does make me sound like an arse, I'm sorry).

My phd was on vortex merging and breakdown between two flat plates, and no, you may not read it - the research was paid for by my current employer and as a result it is confidential.

[SLC]

SLC, is this diagram from simoncm what you have been describing? Once I saw this image, it made me think about what you've been saying and it sure made a whole lot more sense! But since you seem to be the closest one to the real issue and have the background, I want to make sure this is what you have really been describing.

Thanks! Sorry to come off sounding like an arse earlier.

I'm not really sure what's going on in this diagram! I'm assuming it is attempting to depict the load vectors, but I'm not entirely sure simoncm has them clear in his head.

I'll just post this image again (wing on left is attached, wing on right is separated):

[autogyro]

I cant understand why some posters make it so complicated SLC.
Downforce goes strait down to the center of the earth and drag goes in the oposite direction to the way the car does. (This aint no airplane).
Work out the flows and forces and the resultant force is one over the other.

Fancy some hobby work on the forces acting on an autogyro rotor SLC?

[Pup]

Verdict: SLC is the better aero engineer, but simoncm is a far better artist.

[volarchico]

I cant understand why some posters make it so complicated SLC.
Downforce goes strait down to the center of the earth and drag goes in the oposite direction to the way the car does. (This aint no airplane).
Work out the flows and forces and the resultant force is one over the other.

The traditional definition of lift & drag is that the forces are respectively perpendicular and parallel to the freestream direction. If you are looking at just the rear wing, this can rotate the vector components like simoncm shows. However, I do understand that downforce points to the ground and drag points out the rear of the vehicle. I just felt I'd provide you a reasoning since you couldn't understand why some posters would not show it how you were thinking. Reality is there aren't "two components" of force anyway, but just one force vector that we arbitrarily choose to break up into orthogonal components of our choosing. That's why the resultant that both SLC and simoncm show are so important.

[Shaddock]

When I imagine the construction of the knee activator, with no moving or flexible parts, I can only see a solution with a hollowed out wall or some hollow duct in the side of the chassis with a hole in it.

The driver puts his knee over/in the hole to activate it (driver activated device). A problem is that the driver might not seal the hole properly with the side of his knee. Then again this depends on what you want to happen in the duct. If you want to stop air loss in the duct, then the drivers knee must seal the hole. If you want to decrease airflow in the duct the drivers knee only has to go inside the hole, into the ducting to block off most of the flow. Just some thoughts. Not saying it can not work even though it seems illegal anyway..but I think the air can be controlled without the driver and the weird ducting. (we still have to establish if the air int he duct is powerful enough to divert the bigger flow).

From scarbsf1


Imagine making a duct for this in the side of the chassis... I don't know.. I have to think hard on it.

Would it be illegal? As the driver turns the wheel his hands enter and change the airflow around the top of the car, isn't this the same principle as with his legs inside the tub.

[horse]

My explanation is pretty clear, as far as I'm concerned. Did you see the crappy MS Paint job I did a couple of pages ago? I simply don't see how I can describe it any clearer than that.

Ok, let me put it this way. Why does the two element wing work differently from a similarly sized single element wing? If it was just a single element, would the effect of stall be the same? I am assuming not, but maybe I'm wrong there. So, if I'm right, what is the effect of splitting the foil, which allows the drag imposed by the wake (is this form drag?) to be minimal in stall? I think my understanding is that the angle of attack of the top element is actually much smaller than its angle to the free stream because of the deflection caused by the main element. That is what simoncm is getting at in his drawings (although I agree there are some odd directions to their resolved vectors).

From the laymans perspective it appears as if the top element has an exceptionally steep AoA and hence the idea of it stalling is a bit like replacing it with a brick, nay, lintel. Do you see the line of argument? To summarise, yes the induced drag is high due to the angle to the free stream, but as the speed (and apparent AoA) is also high, stalling may induce a large parasitic drag, but, by some mechanism, it doesn't.

(I need a glossary! )

[EDIT]: Did a bit more reading and I wanted to ask if the effect is connected to the low aspect ratio of the wing? [/EDIT]

My phd was on vortex merging and breakdown between two flat plates, and no, you may not read it - the research was paid for by my current employer and as a result it is confidential.

Shame. Does that mean you didn't publish? I suppose it doesn't matter so much if you were going straight into industry anyway. Was it numerical or experimental (or analytical???)? If it was numerical, can you say what sort of model you used?

[Pup]

When I imagine the construction of the knee activator, with no moving or flexible parts, I can only see a solution with a hollowed out wall or some hollow duct in the side of the chassis with a hole in it.

The driver puts his knee over/in the hole to activate it (driver activated device). A problem is that the driver might not seal the hole properly with the side of his knee. Then again this depends on what you want to happen in the duct. If you want to stop air loss in the duct, then the drivers knee must seal the hole. If you want to decrease airflow in the duct the drivers knee only has to go inside the hole, into the ducting to block off most of the flow. Just some thoughts. Not saying it can not work even though it seems illegal anyway..but I think the air can be controlled without the driver and the weird ducting. (we still have to establish if the air int he duct is powerful enough to divert the bigger flow).

From scarbsf1


Imagine making a duct for this in the side of the chassis... I don't know.. I have to think hard on it.

Here's one way this could work:

You see that the scoop is split into two chambers. Also remember in the diagram of the fluidic valve that there are two control points. Add pressure to one or the other, and the main flow switches sides. I've been reading up on fluidics a bit, and I gather that the control can be either a continuous stream of air, or it can just be a puff one way of the other, and the main flow will swap sides and remain stable until you 'puff' it the other way.

OK, so if the scoop has two chambers, imagine two flexible hoses then running from the scoop to the rear of the car, connected to the fluidic valve. Now imagine that the hoses are pliable enough that the driver could easily cut off the flow off of one by pressing his knee against it - pinching it closed. Since cutting off the flow of one is equivalent to increasing the pressure of the other, you could effectively switch the main flow back and forth by pinching one hose or the other. Or, if there needed to be a default state, perhaps it could be set up so that the driver would need to maintain pressure on one of the hoses to keep the flow switched.

I'd think this would be a tricky thing for the driver to do, but I figure I'd throw it out there for the sake of conversation. I do think this would be easier to accomplish than having the driver try to cover some hole with his knee. Personally, however, I still think there would be a way for this to all be done without driver input.

[Tbox]

I duno. I think the knee thing is a bit of a red herring.

Bear with me while I rant in a highly uninformed manner to see if I have this right.

They have tested several different kinds of opening. A very narrow one, a square one and a wide one, possibly with two channels.

My understanding (and guess / gut feeling) is something that has already been proposed in this thread and that people seem to agree with broadly. The nosecone inlet is only one of two inlets. The other may be the extra inlet below the roll hoop. The tubes connecting these to the magic fluidics valve (perhaps located just before the engine cover tube to the sharkfin) are going to be quite a substantially different length, follow a different path and even be different bore sizes. This is one way of tuning the system. The other is changing the shape and size of the nozzle inlet. You can also change the shape and size of the roll hoop inlet (we have seen all of this during testing, apart from the tubes).

I would guess that these two inlets are tuneable so that above a certain speed, the valve switches and the rear wing is fed, stalling it. I predict that at different circuits we will see different forms of the inlet and snorkel, tuned according to the desired speed like we already see with cooling requirements. As soon as the car drops below that tuned speed, the wing is unstalled and you have grip for the corners.

No moving parts, no driver operation. The only way it would be declared illegal would be a very broad definition of a moveable aero device, a la the mass damper.

The split inlet of the wide snorkel might be how they're solving the problem of the wing stalling undesirably in high speed corners (Eau rouge syndrome). It could be the case that the broad, two channel inlet is designed such that it doesn't get enough air to switch the flow under yaw.

After all that, however I can see that it would make sense to have the driver be able to switch off the whole system, for safety more than anything else. Cue the tube squeezing conjectures although I'd prefer to think they have a simple flick switch or button (haha) operated valve that the driver can switch the snorkel feed on or off.

Apologies for the uninformed speculation and ranting. I'm aware that it's also merely restating what has already been said.

[bonjon1979]

When I imagine the construction of the knee activator, with no moving or flexible parts, I can only see a solution with a hollowed out wall or some hollow duct in the side of the chassis with a hole in it.

The driver puts his knee over/in the hole to activate it (driver activated device). A problem is that the driver might not seal the hole properly with the side of his knee. Then again this depends on what you want to happen in the duct. If you want to stop air loss in the duct, then the drivers knee must seal the hole. If you want to decrease airflow in the duct the drivers knee only has to go inside the hole, into the ducting to block off most of the flow. Just some thoughts. Not saying it can not work even though it seems illegal anyway..but I think the air can be controlled without the driver and the weird ducting. (we still have to establish if the air int he duct is powerful enough to divert the bigger flow).

From scarbsf1


Imagine making a duct for this in the side of the chassis... I don't know.. I have to think hard on it.

Would it be illegal? As the driver turns the wheel his hands enter and change the airflow around the top of the car, isn't this the same principle as with his legs inside the tub.

Couldn't they use the Benetton 1994 excuse anyway? Ie we had the device on the car but we weren't actually using it...

[Sambo]

The FIA were due to inspect the Mclaren wing on Friday - has there been any news from that or a verdict..??? [-o<