Do stalled wings or diffusers provide more drag to brake?

[g-force_addict]

Stalled wings and diffusers (flow separation) cause more drag.

Does this increased drag creates more braking power overall? Its increased drag compensates the lower downforce thus less braking from the wheel disc brakes?

[horse]

I would say that breaking performance should be improved unless you get a lockup. If the wheels are still turning, then you're getting maximum breaking force, if they lock then the grip level is too low.

[Tommy Cookers]

Stalled wings ...... (flow separation) cause more drag.

a year ago I would have said so, and did say so in some post
however an F1 ('2 element' aka slotted flap) rear wing at its highest AoA imparts a 90deg velocity component to the ambient air
so producing the maximum possible lift coefficient from a wing of the maximum permitted dimensional 'box'
changing the in-slot condition causes seperation behind the flap and a large reduction in the imparted velocity component
both lift coefficient and drag coefficient are reduced
so in F1 such stalling causes less drag, not more drag

the definition of stalling angle is the AoA beyond which the lift coefficient falls
in aviation the drag coefficient (of an aerofoil) always increases with stall/seperation
but slotted flap behaviour beyond stalling is undefined
because flaps are not intended for or designed for stalling and its consequences regarding speed/dynamic pressure

[hollus]

^^^ Witness F-ducts.

[horse]

Is the OP just talking about DRS type stalling or stalling in general, though?

If you were to stall the main plane, for instance, in an air brake fashion (like many modern supercars now do) then you will increase the braking force.

[rjsa]

Braking FFS, nobody is breaking anything.

And I guess the loss of tyre grip from the stall will invalidate any eventual drag gain by a wide margin.

[horse]

Braking FFS, nobody is breaking anything.

Oops. Edited.

And I guess the loss of tyre grip from the stall will invalidate any eventual drag gain by a wide margin.

Why? If the wheel is turning then it's not sliding, so the grip levels are sufficient to transmit the retardation force of the brakes into the road.

[rjsa]

But if the wing stalls DF decreases, tyre loses grip, wheel locks and bingo!

[horse]

But if the wing stalls DF decreases, tyre loses grip, wheel locks and bingo!

Sure, you're right. I guess it depends on whether there is "spare" grip anywhere in the braking phase, considering the reduced contribution of DF as speed reduces.

[rjsa]

But if the wing stalls DF decreases, tyre loses grip, wheel locks and bingo!

Sure, you're right. I guess it depends on whether there is "spare" grip anywhere in the braking phase, considering the reduced contribution of DF as speed reduces.

In that case the driver should be braking harder.

That's the opposite case as you have on a landing airliner, where the opening of the air brakes on top of the wing will both increase drag and reduce lift - what will increase wheel braking capacity.

[horse]

In that case the driver should be braking harder.

So is the stopping distance of an F1 car limited only by the grip of the tyre?

How about the Veyron air break? From wikipedia:

At speeds above 200 km/h (120 mph), the rear wing also acts as an airbrake, snapping to a 55° angle in 0.4 seconds once brakes are applied, providing an additional 0.68 g (6.66 m/s2) of deceleration

[Drewd11]

Look, the simple fact is this: frictional force acting on a solid>frictional force acting on a liquid.
If you can get more grip and therefore more frictional force between the contact patch and the tarmac, you will decelerate quicker, and any amount of extra drag will never make up for the loss of grip that is the result of the loss of downforce. aerodynamic drag will virtually always be negligible compared to the frictional force exerted between two surfaces, especially two surfaces specifically designed to produce maximum grip.

To illustrate: during acceleration, the car is driven by two contact patches. At the top end of the speed range (where drag is at its highest effect), the limiting factor is not traction from the two contact patches driving the car forward, but power to drive those two wheels. In essence, even when drag is as powerful a factor as is possible, the frictional force of two contact patches far surpasses it.
When braking, four contact patches are at work, with a corresponding increase in grip.

The Veyron and mp4-12c airbrakes (conceived by brighter minds than mine: there are some exceedingly complex differential equations that govern optimality here, never minding the aerodynamic calculations) functions not to stall and just create more drag, but also to increase downforce on the back of the car, for two main functions:
a) to increase total downforce, and therefore grip for maximum braking efficiency
b) to counter weight transfer to the front wheels to keep the car balanced to maximise braking from the four contact patches (and to keep drivers from losing the back end under braking).

[rjsa]

In that case the driver should be braking harder.

So is the stopping distance of an F1 car limited only by the grip of the tyre?

How about the Veyron air break? From wikipedia:

At speeds above 200 km/h (120 mph), the rear wing also acts as an airbrake, snapping to a 55° angle in 0.4 seconds once brakes are applied, providing an additional 0.68 g (6.66 m/s2) of deceleration

Stalling a wing in a F1 car to improve braking is pretty much like taking your right foot off the brake pedal in a bike and sliding your shoe on the floor.

Drewd11 coverd the Veryon case pretty well, and it is similar to the airliner case.

[horse]

Look, the simple fact is this: frictional force acting on a solid>frictional force acting on a liquid.

OK, thanks. I was more trying to address the idea that rjsa was suggesting that there was infinite braking potential available and the only thing limiting the retardation of the car was the limit of grip. I'd suggest that the brakes can only work so hard and that additional braking force from drag, should you be able to keep sufficient grip, would not be a bad thing.

[The Veyron airbrakes functions to] a) to increase total downforce, and therefore grip for maximum braking efficiency

I think this enhances my argument. If you can keep your lift coefficient at the same level when putting the wing into stall, then why wouldn't you [stall the wing]? I found this diagram for the lift coefficient of a NACA-0015 aerofoil and you can see that the lift coefficient at 45 degrees is nearly the same as it is at 15 degrees.

[trinidefender]

Ok you all started off on the wrong foot.

To begin with a stalled wing will usually actually produce LESS drag than a working one. This is because there are more than one main type of drag. The main types are parasite and induced. Parasitic drag is can be broken down further into form drag, skin friction and interference drag (at low speeds, at high speeds you start to introduce problems associated with the drag created around the speed of sound where wave drag becomes an issue).

1. Form drag is the result of the shape of the object. A wing with a thicker cross section will create more form drag than one with a thinner cross section. Form drag increases with the square of the velocity. This means the drag rises sharply with an increase of speed.
2. Skin friction is just that. The drag created by the roughness of the surface. Generally rougher surfaces will create thicker boundary layers producing more drag. This also rises with the square of the velocity.
3. Interference drag tends to work closer to the domain of transonic flow (flow near the speed of sound) so therefore doesn't have much use here.

Okay now onto induced drag. Induced drag is the drag created by the lift (downforce in this case) of the wing. Induced drag increases with an increase in angle of attack. As we know F1 wings run massive angles of attack (AoA) to make up for their lack of wing area. There is a key difference between aircraft and cars now. As an aircrafts speed increases it can lower the AoA on the wing because it just has to keep a constant lifting force to maintain altitude. This decrease in AoA reduces induced drag as speed increases. However on downforce producing cars the situation is slightly different. The cars run with a constant angle of attack therefore as speed increases, downforce increases without to much of an effect on drag Vs the parasitic drag which rises steeply as airspeed increases. If you stall a wing then, for the most part, induced drag disappears. So actually stalling a wing reduces drag substantially, especially at the speeds that F1 cars run at. This is the entire concept of the DRS system all cars run, DDRS trailed and run by sauber, mercedes, Lotus and the F-duct run by McLaren. All of these designs do the same thing by stalling a portion of the wing and reducing drag.

Now finally getting onto your question. Since a working wing produces more drag then you will be able to brake harder and have a higher deceleration. Simply more drag means a higher force acting rearward on the car slowing the car faster. Add to that with a working wing you have more downforce exerted on the tyres,you will be able to brake harder without locking them up.

That is one of the reasons aero is so important in F1. More than just cornering, it also aids braking and accelerating out of a corner.