Lotus E20 VD

[Tommy Cookers]

It may not be effective in an aircraft but it is in a car. Stalling of an aircraft wing has certainly to do with wing profile, speed, ... and not only AoA, that's why large transport aircraft are extremely prone to stalling compared to a propeller fighter. Also as stalling an aircraft wing is a continuous process there is a level of unpredictability (small factors can decide if stalled/not stalled), but the systems we see on cars are binary (if off the wing has a very good flow attachment and if on the flow is well detached).

stalling an aircraft wing will always increase the drag coefficient
(for a given profile) stalling has nothing to do with the speed (at actual aircraft speeds short of compressibility effects)
(for a given profile) stalling is only to do with AoA (the real or synthetic pilot controls this via 'stick' position)

the level of unpredictability of the wings relationship with AoA is trivial, and required to be so ((ie the wing is binary)
(in ideal circumstances in some aircraft a continuous stalling process can be developed, but this is not general)

the pilots relationship with AoA cannot be relied upon, so some natural or artificial 'stall warning' is mandatory

there would typically be 3 profiles, ie takeoff, cruise, and landing (in principle each with its own stalling AoA, to be avoided)
(also ice etc degrades the profile in an unaccounted way)

propellor fighters were not uniformly certified, some had no stall warning behaviour (the opposite to large transports)
(true the propellor helps raise the stalling AoA in some situations, but this is not generally useful eg landing)

good AoA control is analogous to (as in F1) good slip angle control, it's much more difficult at high angles
(simultaneously AoA is disrupted by roll and yaw factors, commonly the 'cause' when critical AoA is accidently exceeded)
(also there are no track markers etc in the air)


back to thread, I agree that F1 needs to reinstate high downforce reliably after DRS etc disengagement
(rather like the behaviour of aircraft)

[superdread]

stalling an aircraft wing will always increase the drag coefficient
(for a given profile) stalling has nothing to do with the speed (at actual aircraft speeds short of compressibility effects)
(for a given profile) stalling is only to do with AoA (the real or synthetic pilot controls this via 'stick' position)

Isn't it rather the kinecticity of the air, as unassisted stalling is raw impulse overcoming the Coanda Effect? And actual aircraft speeds are near enough to Mach 1 for such kinetic effects?
(Is rater off-topic as F1-cars are not planes and not nearly as fast, so unassisted flow separation is improbable.)

the level of unpredictability of the wings relationship with AoA is trivial, and required to be so ((ie the wing is binary)
(in ideal circumstances in some aircraft a continuous stalling process can be developed, but this is not general)

Continuous was the wrong word for what I wanted to convey (sorry). I rather meant, that the point of transition depends on a lot of ambient factors (AoA, air density, air pressure...) and the assisted stalling on race cars can be made to depend on the state of the activation system alone.

propellor fighters were not uniformly certified, some had no stall warning behaviour (the opposite to large transports)
(true the propellor helps raise the stalling AoA in some situations, but this is not generally useful eg landing)

I choose propeller fighters as an example for very nimble aircraft (high climb rates as well) but wanted to avoid the novel aerodynamics on supersonic jet fighters (a whole other can of off topic).

But cars are not really aircraft, and unlike an aircraft you can effectively control a craft with a stalled wing (because you don't steer with the flaps in the wing) and by having a strong enough stalling system you can ensure that the wing is either well attached or well stalled. As for the question wether stalling actually reduces drag, I think a kinetic view (less air is washed upwards, less horizontal impulse converted into vertical impulse) points to yes.

[amc]

As for the question wether stalling actually reduces drag, I think a kinetic view (less air is washed upwards, less horizontal impulse converted into vertical impulse) points to yes.

Yes, but a flat plate moving through air, even at compressible flow speeds, will cause no upwash or downwash, but a hell of a lot of drag. This is effectively what a stalled wing has become, is it not? I see your point that with reduced deflection of air there must be less drag, but working from newton's laws the up-down deflection is what causes lift, and it is the general deceleration of airflow (if you like: forward deflection) that causes drag.

On-topic: I agree, IF there are devices that cause the stalling of the whole wing in F1 then yes, they must be binary and re-attach quickly. But what if 'VD' doesn't stall the wing. If it put high pressure air into a low pressure region behind the wing, not only does it reduce the pressure delta and the drag but it also actively prevents the wing from stalling, rather like blown flaps. I think...

[Tommy Cookers]

I've done some checking .........

at AoAs beyond max Lift Coefficient ('Stall') the Drag Coefficient rises rapidly and continually (with AoA)
similarly the LC falls continually but much more slowly

this applies to the F1 'wing' ie 2 element wing cascade aka wing+slotted flap

operation of aircraft in this region is generally useless and/or impossible due to the catastrophic rise in Cd
operation of an F1 car in this region is unlikely but not unknown (ask Eddy Irvine)

thus we might assume there is a 'Near Post-Stall' region worth consideration
and this region would be larger in F1, mainly due to the low aspect ratios

all this is based on natural airflow eg through the slot ........ ' other airflows are available' , as they say !

[superdread]

Yes, but a flat plate moving through air, even at compressible flow speeds, will cause no upwash or downwash, but a hell of a lot of drag. This is effectively what a stalled wing has become, is it not? I see your point that with reduced deflection of air there must be less drag, but working from newton's laws the up-down deflection is what causes lift, and it is the general deceleration of airflow (if you like: forward deflection) that causes drag.

The wing is not a simple plate perpendicular to the flow, even a stalled wing is still a wing profile and the upper side works as it should, just the lower side creates no more upwash.

On-topic: I agree, IF there are devices that cause the stalling of the whole wing in F1 then yes, they must be binary and re-attach quickly. But what if 'VD' doesn't stall the wing. If it put high pressure air into a low pressure region behind the wing, not only does it reduce the pressure delta and the drag but it also actively prevents the wing from stalling, rather like blown flaps. I think...

If they blow straight backwards they could just affect a little span of the wing.

[Tommy Cookers]

are you saying that a parachute produces (relatively) little drag at AoA of 90deg ?

if not, how is it different to a wing at the same angle ? ... or are you saying the wing is ok till 95deg, or 100deg ?

the 'cobra' manoeuvre (eg thrust-vectoring Su-27 reaching 112deg AoA) is to show extreme in-flight braking&recovery

a plane with a clearly subsonic wing section eg Extra 230 etc will fly at 60deg AoA continuously in straight & level flight at around 20-30 mph, clearly showing very high drag from the wing

[superdread]

are you saying that a parachute produces (relatively) little drag at AoA of 90deg ?

if not, how is it different to a wing at the same angle ?

A parachute hardly qualifies as an aerofoil, so as an example it is far fetched. Also you have the wrong causality when you say stalling -> higher AoA -> higher drag, especially as the wing on a car has no real change in AoA and the alleged stalling effects are not caused by changing the AoA.

[Tommy Cookers]

for any wing or similar there is a max lift coefficient AoA

below this AoA the wing behaves, above this AoA the wing has stalled (badly or otherwise) ...... very simple

typical AoA Cl max is 15deg, for a modern fighter or F1 car it is around 25deg due to the very low aspect ratio


what first caught my attention was the post that suggested that we should avoid using the term 'Stall' when talking F1 !!

[gato azul]

I've done some checking .........

at AoAs beyond max Lift Coefficient ('Stall') the Drag Coefficient rises rapidly and continually (with AoA)
similarly the LC falls continually but much more slowly

Unfortunately you checked for something which is pretty irrelevant for the discussion at hand.
There is no stall mechanism due to increased AoA in the F1 wing case, so this comparison to an aircraft regime is pretty mood.
As you increase AoA on a flat plate/barn door or wing, you change the form(drag) of this object, quite significantly, which
adds for the increase in drag.
There is a reason that aircraft wings get tested for drag at zero lift.

So, if you look for anything remotely wing related, you would look for a wing at or close to max lift position and then see what happens, to lift and drag when you increase velocity (freesteam).
No change of AoA comes into play in the F-duct / VD wing example.

DRS is a different matter, because you change the form/shape frontal area of the wing, is closer to reducing flaps on a aircraft after take off etc. But I think any direct comparisons to aircraft's operational conditions will not bring us much further, because they are just to different.
An aircraft, does not have any "need" to produce excess lift in level flight, it just needs to produce enough upwards force (lift) to overcome it's own mass (weight) to not "fall out of the sky".

I read an interview yesterday, in which one of the Sauber engineers said, that there car is optimized (aerodynamics) to ~200 km/h, which I would take as to say, that they have there best L/D at this speed.

Anyway, a couple of years ago, it was quite "in fashion" to "........." a wing (make it shed drag & downforce) by letting the upper element (flap) bend under load and close the gap, between the main plane and the flap.
If this technique would have been counterproductive, then I doubt that the FIA would have stepped in to mandate the slotgap separators, which are mandatory now.

On a slightly related note, some F3000 teams used to mount the beam wing upside down in Monza couple of years ago, and found a increase in top speed, during a test. ( due to the rules, you could not run without wings/flaps/beam wings etc., you had to have them on the cars in one of the predefined positions).
FIA did not like it too much, and issued a bulletin, saying that cars running this during the following race weekend would be excluded - one team was later excluded after the race for this.

Just look at the formula for induced drag on a wing, that pretty much gives you the answer:

As you increase lift, you increase drag, all other things being the same
The total drag coefficient is equal to the drag coefficient at zero lift (Cdo), plus the induced drag coefficient.
Cd = Cd0 + Cl^2 / ( pi * Ar * e)

As normal cars, don't normally generate large amounts of lift or downforce, Cdi is often ignored, and Cd is only made up from Form/Pressure drag and skin frictional drag etc.
But for and F1 or race car which produces large amounts of downforce it can't (should not be ignored)

Now on a "normal"/fixed wing, to increase Cl you increase AoA, until the critical AoA, but if you find a way to increase Cl
by other means (CC wing etc.) you still have the dependency of Cdi from Cl even if you take AoA out of the picture.

Don't get fouled by diagrams like this:


which seem to show, that induced drag reduces with speed, while form drag and parasitic drag increases with speed.

This diagram, shows the contributions of the different forms of drag, on a operational aircraft under normal operational conditions. And because the aircraft has no need/use for any excess lift, it will reduce Cl from the wings as it flights faster.
Because it is not concerned with Cl, it only needs Lift (a force) to maintain level flight, as it fly's faster a given wing with a given Cl will produce more lift (force), but also more drag.
Because the extra lift (force) is not needed (in level flight) the pilot will try to reduce Cl from the wing, and by doing so, he reduces induced drag as well.
But this has nothing to do with a F1 car at increasing speeds, where AoA does not change and where the Cl of the wing is more or less fixed.
Furthermore, they , want to produce "excessive" lift/downforce as faster as they go ,until they come onto the straights.

[godlameroso]

I don't like to rubbish the theory n_smilke, as there's clearly a lot of work gone into this. However, have you considered directing the flow backwards? I posted a figure earlier that this reduces about 8-12% of the rear wing's total drag, which is a fairly minimal amount, indicating the VD only works on a very small amount of the wing.

Looking at the CFD, I can tell you why downforce drops and drag doesn't. High pressure air is being pumped straight into a low pressure region necessary for downforce, and with a lower pressure delta there is gong to be less force. Drag isn't reduced much because air is actually pulled back towards the wing to fill the area behind the pylon, which is now vacant of any flow from in front of the wing. Just look at the arrows - they show that air from in front of the wing is moving away from that area, and air behind the wing is being pulled downwards. The low pressure behind the pylon is actually bigger in the third diagram, causing more drag.

Just try pointing the slots backwards and putting flow directly behind the pylon. The low pressure peaks will be untouched, but the arrows that point downwards behind the pylon in the first picture will suddenly point upwards. Faster flow behind the wing means less drag.

Stalling a wing, in the sense that the boundary layer separates, is not an effective way of reducing drag. It becomes very unpredictable and isn't generally a good thing. In this sense VD, F-ducts and DDRS don't stall their respective wings. Stalling an aircraft wing is not directly to do with speed, slots, blown slots, camber etc. but angle of attack, which increases as the plane slows due to the CoP movement away from the CoG. In fact, DRS doesn't stall the wing either - it just reduces drag and downforce proportionally.

VD, F-duct and DDRS all reduce drag on a wing, and the reason it is mistakenly called 'stalling' is that the amount of downforce produced drops. But that's not really what stalling means. I would like to steer clear of 'stalling' talk as this is a confusing term which can have many different meanings. If an F1 wing were to truly stall at any speed there would be serious problems. It would have a similar effect to Hakkinen's crash at Hockenheim where the rear wing simply broke off. To be avoided.

So does this imply that instead of "stalling" a wing what is actually happening is that airflow before the wing is being conditioned so that when it interacts with the wing, it's angle of attack is artificially lowered by said conditioning(ala drs)? We see the rooster tails in the rain, so it's not impossible to assume the airflow is following a similar trajectory, perhaps the Lotus system shifts this flow to artificially induce a lower AoA on the beam wing. Could this also be why F1 cars can get away with using extreme angles of attack on the wings? In other words, the wings have to be shaped with extreme AoA because they are taking advantage of the air mass upwash caused by the rest of the chassis.

Furthermore, has anyone taken a look at the rear of the RB8 at hungary, how the diffuser was more sculpted to take advantage of the airflow upwash caused by the rest of it's chassis? It's amazing the little details of human ingenuity.

[hollus]

F1 rear wings and aircraft wings are designed with different objectives and with different constraints. So I agree, "stall" means very different things in the two backgrounds. One key difference is that fact that the F1 wing is always there, its AoA never changes.

To orient discussion I'd like to introduce some rough numbers. Xpensive once calculated that at terminal speed a F1 car creates 1G of deceleration, mostly due to drag. That's a beautiful reference round number for calculations. That is the engine power at the point where the car stops accelerating. So, let's say 600Kg (6000N) of drag at terminal speed (approx. 300Km/h).

Now lets assume that the rear wing is a useless barn door. Look at the car from the front. It is contributing about 1/3 of the total cross section of the car. So our totally useless, fully stalled read wing produces about 200Kg (2000N) of drag.

Now, how much drag is created by the actual working of the wing? First I'll postulate that a perfectly working wing steals as much horizontal kinetic energy from the air as it adds vertical kinetic energy to the same air. Not sure this is quite exact, but can't be far from true, at least at the kind of 45 degree effective AoA of a rear wing, as a similar results comes from this plane with high pressure above (in front) and low pressure below (behind) model (and conservation of energy pretty much requires the trade-off). How much downforce is created by the wing, say 600Kg? Difficult to say, as it doesn't work in isolation, but likely that's about 1/3 of the total downforce. Does it sound fair? Does anyone have better numbers?

So a working wing creates several times more drag by working (by creating downforce) as by being a barn door in the way of the airflow.

You can call it stall (separating the flow), you can call it reducing (actually increasing) the low pressure in the lower surface while keeping the flow attached (reducing the upwash). I don't know if we get one or the other here, but just about any mechanism that reduces downforce generation from an F1 rear wing will also result in a reduction of drag, as the effect of the working rear wing is much larger than the effect of the barn-door, worse case scenario for the rear wing.
Stall it, and you'll reduce drag. Reduce its effective AoA, and you'll also reduce drag. Pick your favorite solution.

[Tommy Cookers]

So, let's say 600Kg (6000N) of drag at terminal speed (approx. 300Km/h).

Now lets assume that the rear wing is a useless barn door. Look at the car from the front. It is contributing about 1/3 of the total cross section of the car. So our totally useless, fully stalled read wing produces about 200Kg (2000N) of drag.

Now, how much drag is created by the actual working of the wing? First I'll postulate that a perfectly working wing steals as much horizontal kinetic energy from the air as it adds vertical kinetic energy to the same air.

So a working wing creates several times more drag by working (by creating downforce) as by being a barn door in the way of the airflow.

if the wing is a useless barn door (and is 33% of the total cross section) it must produce more than 33% of the total drag (unless the whole car has a Cd equally bad as the wings, so the wing drag is much more than 2000N, maybe 4000N ?

the working wing creates the required amount of upwash (adding vertical KE) with the least addition of horizontal KE

your reasoning IMO would support parity of drag for the hard-working wing and the useless 90deg AoA wing

[hollus]

OK, I might have taken logic one step too far with the post above. Going into thinking mode...

P.S. But then the "perfect" barn door is not at 90 degrees either, but still at 45 degrees, so 400Kg of drag looks like an overstatement too.

[bhall]

Crude representation? Yes, very.

[Cam]

A picture is worth thousand words and a +1. Nice demonstration and I reckon most people will understand that. Good job.