Reducing the drag of a two element wing through stall

[Pup]

The question I've had all along is whether something like this actually needs driver interaction. I mean, if they're using air pressure to control the valve, couldn't the system be tuned so that it is activated automatically at a some speed, using the associated change in air pressure at some location on the car - perhaps even the snorkel?

[feynman]

The inlet is located near his knee, that doesn't mean the switching mechanism is. If there is a switch (FIA movable devices permitting), i'd guess it's be an extra pedal down beside the brakes.

The inlet is where it is probably to make use of the cockpit access-panel that has always been there, and any additional holes and inlets nearer the front of the car could have complicated the crash-test, and the tub strength.

I wouldn't imagine they would be trying to use it through Eau Rouge, but coming up the Kemel straight, the left leg has nothing else to do, so stand on the lever and deploy the special aero magic.

[vall]

The question I've had all along is whether something like this actually needs driver interaction. I mean, if they're using air pressure to control the valve, couldn't the system be tuned so that it is activated automatically at a some speed, using the associated change in air pressure at some location on the car - perhaps even the snorkel?

I may have missed something, but if there is a valve involved it must be a moving device by the FIA understanding. How it could be legal then?

[segedunum]

I've never liked the driver intervention and 'knee' activation. It's just far too impractical to work for what would be a sensitive device. However, we have three options:

1. A pedal switch option - this would certainly be deemed to be a moveable aerodynamic device. Such things have been banned before.

2. The rather passive 'knee' option. This gets around the restriction of 1, in theory, and could be claimed to be for cockpit cooling. However, I see it being too imprecise to work properly and once the stewards discover that this flow is connected to the rear of the car then it can only be deemed to be sailing close to the regulations. It is, however, probably the most plausible and safest option, if not the most practical.

3. A completely self-contained system where the right conditions are tripped at high speed to activate the stall. Again, this is complex to get right because it has to be sensitive enough to come on at the right times. You might gain 10 mph in a straight line but if it doesn't turn off right into corners than it will cost you a lot more time. The losses are a lot bigger than the gains if it doesn't work.

Red Bull may be blase about it and Ferrari may be silent, but I can see the 'clarification' turn into a smoke and mirrors protest at Bahrain once stewarding starts. There seems an element of kidology from Horner about him being sure that it is legal.

[Pup]

I may have missed something, but if there is a valve involved it must be a moving device by the FIA understanding. How it could be legal then?

Yes, go back three or four pages for the discussion on fluidics. There's a type of valve using airflow that has no moving parts.

[SLC]

SLC, I think your terminology might confuse some people who are using the wikipedia articles on drag to follow along. What you're calling 'pressure drag' is in fact referred to on wikipedia as 'induced drag': induced drag; and I think what you call 'induced drag' is the same as what they call 'form drag': form drag

I think you might want to re-read that Wiki article. My usage of the drag terms is correct.

Parasitic drag = skin friction drag + pressure drag + interference drag (interference is more aircraft specific, though).

Induced drag = lift dependent drag (due to the trailing vortex system changing the effective incidence onto the wing element - this is NOT really relevant to our current stall/drag discussion).

Total drag = Parasitic drag + Induced drag

Sure. Understand that I'm not disagreeing with you - only lamenting that the definitions of these terms aren't fully explained in wikipedia, which unfortunately is the reference of choice for most. You're referring to presure-induced drag as 'induced drag', while I'm referring to dynamic induced drag.

I'm sure it seems picky, but you see how it can be confusing when I say that this is all about induced drag, and you say it has nothing to do with induced drag when we're both talking about the same thing.

The root of the problem is this...

First, let's consider dynamic induced drag, shown in Figure 4-8. If you hold your hand out of the window of a moving car, with the front edge tipped up at an angle to the relative wind to give it an angle of attack, you will feel a force pushing your hand back, but also slightly upward. In other words, depending on the angle of attack, there will be a force backward (induced drag) and a force upward (lift). The amount of force in each direction will depend on the angle of attack. If the angle of attack is small, the drag and lift are comparatively small. Any increase in angle of attack, up to a certain point, will increase drag and lift. However, at very high angles of attack, approaching the stall point, lift will decrease and the drag will overcome lift and thrust with an accompanying loss of speed and attitude. If you were to hold your hand vertical to the relative wind, the only force would be backward; that is, all dynamic drag and no lift.

Now let's consider pressure-induced drag, which can be divided into the two types. You will remember that the thin layer of air over the upper surface of the wing will break away from the wing at high angles of attack and that the flow will become turbulent as the flow of air breaks away from the wing. This turbulence results in pressure drag and loss of lift. Turbulence and pressure drag also result from the flow of air around the wingtip as the comparatively high-pressure air under the wing flows over the wingtip to the low-pressure area on top of the wing.

Perhaps it would be better to just refer to the 'wing vector' and to 'drag' as the relevant forces?

In my 10 years of studying and/or working in aircraft and F1 aerodynamics I have never come across the phrases dynamic-induced or pressure-induced drag.

As far as I'm concerned (along with the higher education system within the UK!) induced drag is the additional drag component that is added to the system by the change in effective incidence onto a wing due to the wing's trailing vortex system. For an F1 rear wing this is actually a pretty insignificant drag source.

What is your background in terms of aero or engineering?

[mike_dangerous]

It would probably work to have it controlled by speed, but you also want the downforce and drag of the unstalled wing during braking, so as soon as the driver brakes you want the wing to be unstalled, not once the driver has slowed down sufficiently.

[SLC]

Dear F1 fans,

I think you all need to get some explanation about what is going on with the McLaren rear wing. As an aerodynamicist, I was very puzzled when I read about the “stalling” issue. Actually, I realized that it comes all from some confusions with the terminology.
In aerodynamics, the term “stalling” refers to a drop of lift (or downforce) due to highly separated flow at the upper (or lower for cars) surface of a wing. This will produce a significant increase of drag no matter the wing you refer to (included the “highly cambered and high lift generator wing”). So any post-stall situation should be prohibited whatsoever.

HOWEVER, you can improve the performance of any wings before stall by blowing some air on the upper (or lower for cars) surface on the wing. You increase slightly the boundary layer speed and in turns, you can increase significantly the lift (or downforce) generated – almost twice more – but you also increase a bit the drag. A solution to blow some air in the upper (or lower for cars) surface can be done with a small slot on this surface. This is a known theory, for instance, this has been tested for wings in 1929, see the Figure I enclosed (I took them from I. Abbot, Thoery of wind section, 1959).



Now, imagine that you are on a straight line and that you remove the action of the slot, you will switch from one wing situation (high lift, higher drag) to another (normal lift, normal drag). You have lowered the drag and lift, but please, don’t call that “stalling”!

Considering the McLaren rear wing, since I am not the designer of this car and do not have access to the data, I can’t tell if this is what they want to achieve.

Finally, I guess this is what C. Horner and most of people from F1 who are aware of such practice but don’t really understand the physics, call “stalling the wing”.

Now, I reckon that it is all about “trade off” because such solution, if this is actually implemented in some way, would be difficult to control accurately and might lead to situations where some downforce will be missing for the braking moments. But that’s another debate.

Sincerely,
Tristan

Tristan, no offence intended here, but by what means exactly do you call yourself an "aerodynamicist"? Are you a student?

The top wing is stalling in every sense of the word. Separated, reversed flow in the boundary layer. Flow no longer being able to withstand the pressure recovery/gradient along the suction surface of the aerofoil.

You go and quote a page for some text book - showing a simple, single aerofoil profile. Yes, when this stalls, Cd increases. But, and this is the fifth time I say this, we are not dealing with a single aerofoil section. You have to differentiate between these different cases.

When a top rear wing stalls in F1 you do get an increase in turbulent losses (ie, skin friction), you do get decreased pressure recovery, and you do get a massive decrease in load production. The wing is stalled. It just so happens that the decrease in pressure drag (due to the highly angled overall load vector) dwarfs these smaller effects - and so the overall car Cd drops.

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.

[RacingManiac]

consider that Renault's TMD can be classed as movable aero devices, and that flexi-wing is supposed to be banned and this is not located in the brake ducting area(as with the winglets on the brake duct), I don't see any actuated version of the blown wing can be legal....driver controlled or reactive....

[Pup]

In my 10 years of studying and/or working in aircraft and F1 aerodynamics I have never come across the phrases dynamic-induced or pressure-induced drag.

Perhaps it's a US/Brit thing, like the way you guys mispronounce schedule.

What is your background in terms of aero or engineering?

Basically, I look like this 80% of the time I'm reading anything here --->
like this, 15% of the time --->
and this, 5% of the time --->

I'm feeling pretty stoked that someone would even ask!

[PlatinumZealot]

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.

[bidong]

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.

=D>

[horse]

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?

[Just_a_fan]

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?

Since when was a degree a prerequisite of understanding something? Indeed, looking at some of the young graduates around these days, one wonders if some degrees are anything more than CV fillers...

[ringo]

flow is attached to the sides more than the centre of the wing. Upper element's flow is attached throughout because of the slot. Much better improvement than my first attempt which was just a 2D wing which doesn't tell the whole story.
Lift to drag ratio is 1.834 with down-force of 136 lb. on the wing alone
the last one i did was 0.7 L/D.

This isn't really important but just correcting myself. I made a mistake when i said the downforce was 136lb, that's just half of the wing It's more like 272lb on the rear wing. Assuming that the rear wing is only about 25% of the total, it's stand to reason if i made the full car it would be about 1088lb of downforce at 90m/s.
Lift to mass ratio of 0.797, it can't drive upside down in any tunnels, but not too bad.

back to the regularly scheduled program!