McLaren MP4-31 Honda

[DiogoBrand]

Do these new vertical slots on McLaren rear wing endplate increase downforce and drag by mixing the outside air and giving more airflow hence more upwash effect on rear wing and diffuser? Or they reduce drag (and downforce) in some way (how)?

Piola and Sommers on Motorsport say This aggressive design should not only increase downforce but reduce drag too, as the designers continue to search for maximum efficiency.


Which is impossible because every downforce brings its induced drag with it...

Impossible that the rear wing has increased downforce. You are introducing neutral pressure flow into a low pressure area, which inevitable leads to a decreased downforce production and indeed even a decreased efficiency of the aerofoil. It does reduce drag.

Unless I am missing something, they are doing this to keep rear wing upwash linked with diffuser upwash by having a big AoA wing.

So basically they're introducing "negative outwash" to be able to balance it out with more upwash. The question is: does the added upwash make up for the lost outwash? I guess they're gonna know after today.

[PhillipM]

It's only a solution you could ever use with a low downforce setup.

[turbof1]

Do these new vertical slots on McLaren rear wing endplate increase downforce and drag by mixing the outside air and giving more airflow hence more upwash effect on rear wing and diffuser? Or they reduce drag (and downforce) in some way (how)?

Piola and Sommers on Motorsport say This aggressive design should not only increase downforce but reduce drag too, as the designers continue to search for maximum efficiency.


Which is impossible because every downforce brings its induced drag with it...

Impossible that the rear wing has increased downforce. You are introducing neutral pressure flow into a low pressure area, which inevitable leads to a decreased downforce production and indeed even a decreased efficiency of the aerofoil. It does reduce drag.

Unless I am missing something, they are doing this to keep rear wing upwash linked with diffuser upwash by having a big AoA wing.

So basically they're introducing "negative outwash" to be able to balance it out with more upwash. The question is: does the added upwash make up for the lost outwash? I guess they're gonna know after today.

No, that is a wrong statement. It might, and I put emphasis on might because this simply could be false, have a negative impact on your outwash, which is not the same as stating that they purposely want to do so. You'll always have outwash, and the way the trailling edge is bended outwards indicates strongly McLaren still wants to boost outwash.

They are injecting higher pressure flow into the low pressure side of the aerofoil. Given the high angle of the wing, this comes with certain wanted benefits and certain unwanted disadvantages, which is not just a matter of outwash vs upwash as you are effectively and purposely trying to run a very poorly working rear wing (in isolation, as the end goal is still to drive the diffuser).

[Chuckjr]

I wonder if the shift in airflow behind the Macca will affect the car following it differently than cars which don't have this shift.

[turbof1]

I wonder if the shift in airflow behind the Macca will affect the car following it differently than cars which don't have this shift.

Probably yes. If what I envision to be true and mclaren retains a better upwash along with less pressure differential then other cars which have shallower rear wings, the wake should be cleaner, meaning the trailling car could potentially follow closer relative to the rest of the field.

[DiogoBrand]

No, that is a wrong statement. It might, and I put emphasis on might because this simply could be false, have a negative impact on your outwash, which is not the same as stating that they purposely want to do so. You'll always have outwash, and the way the trailling edge is bended outwards indicates strongly McLaren still wants to boost outwash.

They are injecting higher pressure flow into the low pressure side of the aerofoil. Given the high angle of the wing, this comes with certain wanted benefits and certain unwanted disadvantages, which is not just a matter of outwash vs upwash as you are effectively and purposely trying to run a very poorly working rear wing (in isolation, as the end goal is still to drive the diffuser).

My first impression was that they were trying to shove more air within the endplates, therefore accelerating it, lowering the pressure and "pulling" the air from the diffuser. But we may never know what's the purpose of those slots, for all we know it may just be a terrible idea and not work at all. Let's wait and see.

[turbof1]

My first impression was that they were trying to shove more air within the endplates, therefore accelerating it, lowering the pressure and "pulling" the air from the diffuser. But we may never know what's the purpose of those slots, for all we know it may just be a terrible idea and not work at all. Let's wait and see.

You are accelerating the flow on the outside of the plate, but slowing down the flow on the inside, underneath the rear wing. This is because your flow on the underside of the wing is very low pressure, while the pressure of the flow on the outside which is diverted to the inside, is more or less neutral. What you'll get is flow on the outside and inside of the plate being closer to one another in terms of pressure. Accelerating flow only works if you increase the difference in pressure, which is the opposite McLaren is doing.

And yes, this might indeed be a terrible idea. It'll probably will mimic the intentions, but might not bring the performance envisioned.

[PlatinumZealot]

Those endplates are clearly for drag reduction. It reduces the pressure gradient at the trailing end of the endplate and as such the vorticity is reduced and hence drag is reduced.

It reduces the downforce at the outboard ends of the main plane somewuat too. All in all this is about cutting more drag.

[GoranF1]

http://www.motorsport.com/f1/news/mclar ... ia-794542/

McLaren decides not to race radical wing in Austria

[diffuser]

Those endplates are clearly for drag reduction. It reduces the pressure gradient at the trailing end of the endplate and as such the vorticity is reduced and hence drag is reduced.

It reduces the downforce at the outboard ends of the main plane somewuat too. All in all this is about cutting more drag.

There had also been talk of lack of upwash since the beam wing was removed . I wonder if the additional pulled air into the centre also accelerates the air under the rear wing. That would result in more downforce.

[PlatinumZealot]

The floor being the same, you can roughly relate the strength of the up-wash to the amount of down-force the car is making. The up-wash is really due the low pressure behind the car combined with the curvature of the RW, Diffuser, brake ducts and wake of the rear tyres. Those big endplate slots only guide more air into the area..Just like how the other end-plates slots work but only on a bigger scale.

I think if Mclaren were seeing equal or more down-force from the wing they would more than likely keep it. Having stable rear, less graining, not so bad a problem to have right? But I think the opposite happened. The lost too much stability at the rear - maybe the wing was working OK but only in a certain speed range.. but the risk was too much to keep it on for the race which is expected to be tough on tyres.

[bhall II]

I don't know if it can be taken for granted that somehow normalizing pressure between the endplates would reduce drag. Yes, drag borne by tip vortices would likely fall. However, increasing static pressure means reducing dynamic pressure (velocity), because total pressure is constant, and reducing the dynamic pressure of air flow between the endplates inherently means reducing the dynamic pressure of air flow upstream, because downstream events have upstream consequences. Such a strategy would create a bottleneck, which is the polar opposite of efficient.

(EDIT: I've parsed that so many times in my head that it no longer appears to be language, much less coherent English. If it doesn't make sense, let me know, and I'll try to clarify.)

Plus, there are no immediate signs of stagnation in the FloVis streaks...



What seems more likely is that the slots effectively increase dynamic pressure - as always.

For the last couple of years, both McLaren and Red Bull have run diffusers that maximize expansion via geometries that make use of every legal millimeter available between the rear wheels...



For comparison, here's SF16-H...



Presumably, the idea is to couple the edges of the diffuser to the upwash created by the brake ducts in much the same way diffusers were formerly coupled to the upwash created by the beam wing. If so, reducing the air flow that passes between the rear wheels and the outside of each endplate by way of full-length slots that reroute such air flow between the endplates would allow for more upwash from the brake ducts, which would then increase efficiency at the edges of the diffuser.

Ultimately, it would allow the rear wing to be set at a proportionally lower AoA with less consequential loss of underbody efficiency compared to the former design. In other words, same downforce, less drag (or any permutation thereof).

At least, that's how I see it.

[diffuser]

The floor being the same, you can roughly relate the strength of the up-wash to the amount of down-force the car is making. The up-wash is really due the low pressure behind the car combined with the curvature of the RW, Diffuser, brake ducts and wake of the rear tyres. Those big endplate slots only guide more air into the area..Just like how the other end-plates slots work but only on a bigger scale.

I think if Mclaren were seeing equal or more down-force from the wing they would more than likely keep it. Having stable rear, less graining, not so bad a problem to have right? But I think the opposite happened. The lost too much stability at the rear - maybe the wing was working OK but only in a certain speed range.. but the risk was too much to keep it on for the race which is expected to be tough on tyres.

All we know is that they said they didn't run it enough in FP (cause of the weather) to feel comfortable with running it in the race. For all we know, it worked like a charm, they were just worried it would fall apart during the race.

From http://www.motorsport.com/f1/news/mclar ... ia-794542/
"McLaren evaluated the data from the wing overnight but felt it would be too much of a gamble to race with it having not got the mileage it wanted under its belt."

[Moose]

Do these new vertical slots on McLaren rear wing endplate increase downforce and drag by mixing the outside air and giving more airflow hence more upwash effect on rear wing and diffuser? Or they reduce drag (and downforce) in some way (how)?

Piola and Sommers on Motorsport say This aggressive design should not only increase downforce but reduce drag too, as the designers continue to search for maximum efficiency.


Which is impossible because every downforce brings its induced drag with it...

Impossible that the rear wing has increased downforce. You are introducing neutral pressure flow into a low pressure area, which inevitable leads to a decreased downforce production and indeed even a decreased efficiency of the aerofoil. It does reduce drag.

Unless I am missing something, they are doing this to keep rear wing upwash linked with diffuser upwash by having a big AoA wing.

"Introducing air into a low pressure area can never increase downforce" is a very poor argument, there are several examples of doing exactly that used on every single car. Every single slot in a wing is an example of introducing higher pressure air to a low pressure area and in doing so increasing downforce (by keeping the air better attached in the low pressure area, and allowing a steeper AoA).

[Moose]

My first impression was that they were trying to shove more air within the endplates, therefore accelerating it, lowering the pressure and "pulling" the air from the diffuser. But we may never know what's the purpose of those slots, for all we know it may just be a terrible idea and not work at all. Let's wait and see.

You are accelerating the flow on the outside of the plate, but slowing down the flow on the inside, underneath the rear wing.

Sure, you're doing that in this design, but in doing so, you may be allowing a steeper AoA of the rear wing, and in fact accelerating it compared to a design without these slots.