Why the cut outs in rear wing endplates?

[Crafty]

I've got a basic understanding of aero, but have a question and wondered if any of the clever people can answer it..

In the past few years the end plates of rear wings have sported cut outs, they also have vents in front of the wing plane.

MP4-25


RB6


F10


So what is the cutout for and why the vents ?
I can remember seeing vortices coming off rear wings on older cars, which (I guess) is air being pushed away from the end plate, so does the cut out mean less disturbance ?
Are the vents to create a low pressure area ?

[ESPImperium]

Simple answer, lets air out and creates a small ammount of downforce performance gain.

[wesley123]

These vents manage the vortexes better on the rear wing end plate increasing its performance.

These cut outs are kind of a guess for me, but I guess these cutouts reduce pressure behind the wing and energize the flow, increasing downforce a bit

[Jersey Tom]

I'm a tire guy rather than aero, but my limited understanding is the intent of not having big solid end plates is to allow better flow along the wing when the car is at a non-zero yaw angle (eg, mid corner)

[ringo]

This is what it looks like, but i didn't really see what was happening at the time.

I added the vertical gurneys and the extended the low pressure under the wing, but the cutouts weren't obvious.
It may be vortex drag related if we note the interaction with the flow through the vents. The vortex curls over at a lower height, to the benefit of what? i have no clue.

[Tim.Wright]

Sureley there has to be an aero guy here who knows what they are for.

But failing that I will add to the conjecture. I have heard it is to bleed high pressure air off the wing at very high speeds to reduce drag.

My thinking is that you have a high static pressure caught in between the wing and end plates which gives you down force, but as you increase in speed, the static pressure increases. So the geometry of the slots could make the wing characteristics a bit more digressive at high speed to reduce drag (but also downforce)

Or maybe I will also stick to tyres and suspension too.

Tim

[Just_a_fan]

Wings work because they have high pressure on one side and low pressure on the other (in simple terms). Naturally, the high pressure air wants to move in to the low pressure area (this is obvious in everyday life). To do this, it rolls around the end of the wing. This is fine. However, the wing is moving forward so the air rolling round the end forms a spiral - the vortex we see sometimes. On aircraft, the vortext is reduced by the little upturned ends we see on modern airliners.

Why is this important? Because the vortex has the effect of reducing the effective span of the wing. And if you reduce the span you reduce the lift (because lift is a function of the pressure difference per square metre of wing surface).

Wing endplates are very good at reducing this issue which is why F1 wings can generate so much downforce. However, because the rules limit the position of the rear wing and the teams want it as high as possible (for clean airflow), the wing is close to the top of the endplates. The 'bubble' of high pressure above the wing builds up and spills over the top of the endplate. This means the vortex can be generated afterall. By putting slots in the endplate the teams allow some of the high pressure air to bleed in to the low pressure air outside the endplate (lower pressure because it is moving quicker than the air above the wing).

What vortex is created is going to be rolling anti-clockwise (looking at the left side endplate looking from the front). The area behind the wing on the inside of the endplate is at lower pressure. By putting a cut out in this area the teams allow some of the low pressure area to try to set up a clockwise vortex. This counters the anti-clockwise flow and so reduces the overall vortex created.

The vortex has another effect - it creates drag because it contains a lot of energy; energy that has come from the car. Reduce the vortex and you reduce the drag and increase the downforce.

In summary, the slots and cut out improve the overall L/D of the car.

[forty-two]

What a thorough answer to a question I've been confused about for some time!

Well done Justafan!

[Just_a_fan]

Thanks. I'm no aero guy though so am happy for someone with more thorough knowledge to correct me.

[Henning]

Brilliant explanatory post just-a-fan. Thanks.

[SEBA_406]

Excellent!!! Thanks for the explanation...

[Callum]

Probably the most clear and understandable explanation on this site!

[Sayshina]

There's been several articles in racecar engineering over the last couple of years on wings, and while just a fan is mostly correct, it's much more complex than that. The summary is that wings make more downforce/lift than can be explained by the pressure diferential and mass flow direction change.

As to the cutouts, aero guys, some of them in the above articles but also other places, have said they reduce downforce, but reduce drag by a significantly larger margin.

[Formula None]

RB show car:



I've been wondering why FI aren't using louvers this year. My guess is that their DRS actuator is inside the endplates in that area, judging by the thickness.

[marekk]

Nice explanation, Just_a_fun.

Not so sure about this overall vortex reduction mechanism though.
My understanding is, when you allow some high pressure air above the wing to escape, you have to allow some ambient pressure air to enter low pressure area below the wing, to keep longitudal circulation of air symmetric (more or less).
There will be less circulation at wing tips of course, so slightly less downforce but significantly reduced induced drag.

One additional thing (that's why FI has small cutout, even when no vents):

If you place gurney type flap at the trailing edge of airfoil on the high pressure side, air going (very quickly) around sharp edge of the gurney will form 2 strong counter rotating vortices, starting at wings root (car center in this case) and going along the gurney to wing tips. Lower vortex "sucks" some air from boundary layer on lower wing's surface, which helps to keep the flows attached. Small cutouts allow for smooth shedding of those vortexes to the outside flow, keeping them rotating and increasing gurney's efficiency.