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[nish2280]

Would the F-Duct become useless when under the tow or the wake of another car? This would be because the airflow to the intake would be inefficient rendering it ineffective?

[Fred_C_Dobbs]

That's what a stalled wing is..... When pressure on each side of the winged surface are relatively the same downforce or lift are no longer created.

Sorry, that's incorrect. That just means it's not generating lift. If that were the case, the wings of an aeroplane parked on the tarmac could be said to be "stalled." Or the carton of milk sitting in my fridge is "stalled." A stall occurs when a wing's angle of attack exceeds its critical angle, causing boundary layer separation. In subsonic aerodynamics, any definition of a stall necessarily must involve boundary layer separation. No boundary layer separation, no stall.

And you can't stall a wing without also inducing a vibration (a consequence of the air becoming turbulent where the boundary layer has separated). I rather doubt Hambone would be very keen on the thought that his rear wing should begin shuddering when he sticks his knee in the hole at 300 kph.

Unfortunately, the majority of the automotive media have too little grounding in aerodynamics to do anything apart parroting the buzzwords they pick up from someone else who they think know what's happening.

I finally found someone who appears to have got it right. Of all sources, Wired magazine has an online article that explains it perfectly. What's happening is the opposite of what's been speculated and, unless my meager Italian fails me, it works the opposite of how it's explained in the video supeindesu linked to.

I don't know why I didn't think of this earlier. Introducing additional airflow into the slot between the wings would not induce a stall. In fact, because of what's known as the Coanda effect, it should be increasing lift (and drag), not decreasing it. "Blown flaps" on STOL aeroplanes have operated on that principle for more than 50 years.

The McLaren's nominal condition is for the flow to be open. The redirected air increases lift all along until [knee in hole], then it's stopped. No Coanda effect means less lift but no extra vibration.

Everything fits. It accomplishes the principal objectives with no untoward side effects.

[darwin dali]

That's what a stalled wing is..... When pressure on each side of the winged surface are relatively the same downforce or lift are no longer created.

Sorry, that's incorrect. That just means it's not generating lift. If that were the case, the wings of an aeroplane parked on the tarmac could be said to be "stalled." Or the carton of milk sitting in my fridge is "stalled." A stall occurs when a wing's angle of attack exceeds its critical angle, causing boundary layer separation. In subsonic aerodynamics, any definition of a stall necessarily must involve boundary layer separation. No boundary layer separation, no stall.

And you can't stall a wing without also inducing a vibration (a consequence of the air becoming turbulent where the boundary layer has separated). I rather doubt Hambone would be very keen on the thought that his rear wing should begin shuddering when he sticks his knee in the hole at 300 kph.

Unfortunately, the majority of the automotive media have too little grounding in aerodynamics to do anything apart parroting the buzzwords they pick up from someone else who they think know what's happening.

I finally found someone who appears to have got it right. Of all sources, Wired magazine has an online article that explains it perfectly. What's happening is the opposite of what's been speculated and, unless my meager Italian fails me, it works the opposite of how it's explained in the video supeindesu linked to.

I don't know why I didn't think of this earlier. Introducing additional airflow into the slot between the wings would not induce a stall. In fact, because of what's known as the Coanda effect, it should be increasing lift (and drag), not decreasing it. "Blown flaps" on STOL aeroplanes have operated on that principle for more than 50 years.

The McLaren's nominal condition is for the flow to be open. The redirected air increases lift all along until [knee in hole], then it's stopped. No Coanda effect means less lift but no extra vibration.

Everything fits. It accomplishes the principal objectives with no untoward side effects.

Quote from your referenced Wired mag article:
'When the driver closes the vent, it essentially stalls the rear wing, thereby reducing drag and increasing speed on the straightaways.'

[Fred_C_Dobbs]

That's what a stalled wing is..... When pressure on each side of the winged surface are relatively the same downforce or lift are no longer created.

Sorry, that's incorrect. That just means it's not generating lift. If that were the case, the wings of an aeroplane parked on the tarmac could be said to be "stalled." Or the carton of milk sitting in my fridge is "stalled." A stall occurs when a wing's angle of attack exceeds its critical angle, causing boundary layer separation. In subsonic aerodynamics, any definition of a stall necessarily must involve boundary layer separation. No boundary layer separation, no stall.

And you can't stall a wing without also inducing a vibration (a consequence of the air becoming turbulent where the boundary layer has separated). I rather doubt Hambone would be very keen on the thought that his rear wing should begin shuddering when he sticks his knee in the hole at 300 kph.

Unfortunately, the majority of the automotive media have too little grounding in aerodynamics to do anything apart parroting the buzzwords they pick up from someone else who they think know what's happening.

I finally found someone who appears to have got it right. Of all sources, Wired magazine has an online article that explains it perfectly. What's happening is the opposite of what's been speculated and, unless my meager Italian fails me, it works the opposite of how it's explained in the video supeindesu linked to.

I don't know why I didn't think of this earlier. Introducing additional airflow into the slot between the wings would not induce a stall. In fact, because of what's known as the Coanda effect, it should be increasing lift (and drag), not decreasing it. "Blown flaps" on STOL aeroplanes have operated on that principle for more than 50 years.

The McLaren's nominal condition is for the flow to be open. The redirected air increases lift all along until [knee in hole], then it's stopped. No Coanda effect means less lift but no extra vibration.

Everything fits. It accomplishes the principal objectives with no untoward side effects.

Quote from your referenced Wired mag article:
'When the driver closes the vent, it essentially stalls the rear wing, thereby reducing drag and increasing speed on the straightaways.'

Wired are not know for the brilliant aerodynamicists on their staff but they did get the most important bit right:
"It is believed that a small air scoop in the nose of the car — you can see it just below the steering wheel in the pic below — allows air to enter a tube that runs through the cockpit and the air intake above the driver’s head to the rear wing. From there it flows to the wing and passes through small slots to the back side of the wing, where the added energy can aid the airflow like the slats on a plane. This increases downforce in the corners." (emphasis added)

The key is he's saying the additional airflow normally is utilized to create extra downforce. The extra airflow is not used to do any stalling or anything of the sort.

Simply reducing lift does not equate to a stall. When a pilot lowers the nose on his aeroplane, it descends because the wing produces less lift at the reduced angle of attack. Does that mean he's stalled it? Of course not, that's absurd.

[darwin dali]

I get that (creating more down force with the extra air flow). However, it clearly states that once the vent is closed, i.e., no more extra air flow, the wing essentially stalls, thereby reducing drag.

[stonemonkey]

Would that mean that the driver would have to keep the hole covered on twisty sections and when braking?

[Fred_C_Dobbs]

I get that (creating more down force with the extra air flow). However, it clearly states that once the vent is closed, i.e., no more extra air flow, the wing essentially stalls, thereby reducing drag.

It either stalls or it doesn't. "Essentially" don't count. No boundary layer separation, no stall. Period. Full stop. On that point, they're at best being over-simplistic. Wrong is closer to the truth.

Their other option is trying to explain the Coanda effect to a public with a 30-second attention span.

Would that mean that the driver would have to keep the hole covered on twisty sections and when braking?

No, the McLaren cars ordinarily produce a bit of extra downforce due to the Coanda effect from that little bit of air forced from the F-duct through the slot in the wing. The knee valve cuts off the flow and, along with it, the Coanda effect.

[stonemonkey]

I get that (creating more down force with the extra air flow). However, it clearly states that once the vent is closed, i.e., no more extra air flow, the wing essentially stalls, thereby reducing drag.

It either stalls or it doesn't. "Essentially" don't count. No boundary layer separation, no stall. Period. Full stop. On that point, they're at best being over-simplistic. Wrong is closer to the truth.

Their other option is trying to explain the Coanda effect to a public with a 30-second attention span.

Would that mean that the driver would have to keep the hole covered on twisty sections and when braking?

No, the McLaren cars ordinarily produce a bit of extra downforce due to the Coanda effect from that little bit of air forced from the F-duct through the slot in the wing. The knee valve cuts off the flow and, along with it, the Coanda effect.

With no moving parts allowed I thought the air normally escaped into the cockpit and covering the hole would force the air through the duct. How could it work the other way? or have I got the moving parts thing wrong?

[bud]

So basically what you're saying is that the rear wing isn't stalled but essentially they are just taking away a percentage of downforce. So say normally the rear wing is running 100% downforce once they close the duct it then runs at say 70% downforce all along creating downforce so cannot be called a stall.
That right Fred?

[f1ea]

Hmm this is interesting...

Simmilar to an overflow ogee spillway design (the section is shaped to follow the natural trajectory of water, to create minnimum loss). In the ogee overflow, there's air injectors to keep the pressure from turning negative when speed increases. So the F-duct seems to work as some kind of air injector to manipulate the working pressures on the wing, not really stalling it...

Nice posts from Fred_C. We got our MVP hehe

[texasmr2]

As with every positive there is a negative regardless of how small it is especially in aerodynamics.

[What's Burning?]

I get that (creating more down force with the extra air flow). However, it clearly states that once the vent is closed, i.e., no more extra air flow, the wing essentially stalls, thereby reducing drag.

It either stalls or it doesn't. "Essentially" don't count. No boundary layer separation, no stall. Period. Full stop. On that point, they're at best being over-simplistic. Wrong is closer to the truth.

Their other option is trying to explain the Coanda effect to a public with a 30-second attention span.

Would that mean that the driver would have to keep the hole covered on twisty sections and when braking?

No, the McLaren cars ordinarily produce a bit of extra downforce due to the Coanda effect from that little bit of air forced from the F-duct through the slot in the wing. The knee valve cuts off the flow and, along with it, the Coanda effect.

An F Duct by any other name...A decrease in downforce by any other name is still a speed gain in a straight line. I think you're explaining this a different way but the theory is still the same whether removing the additional air decreases the total amount of downforce, or adding the air introduces a slight turbulence that lowers the over all effectiveness of the wing.

I think MLraen are the only ones that would be able to confirm which mean they chose to that end.

[nish2280]

My understanding is based on this post.
http://www.racecar-engineering.com/articles/f1/449813/f-ducts-how-do-they-work.html

Seems to make sense to me

[scotty]

So basically what you're saying is that the rear wing isn't stalled but essentially they are just taking away a percentage of downforce. So say normally the rear wing is running 100% downforce once they close the duct it then runs at say 70% downforce all along creating downforce so cannot be called a stall.
That right Fred?

That is my understanding, having been reading more about the system. The McLarens can basically 'turn off' a section of the rear wing and all the associated drag - however, i think these passive versions (ie, Sauber's and the one Ferrari tested in China) have basically tried to manipulate air pressures at high speeds to get a similar effect, but i don't think it's working very well. Unsurprising really, when you consider how it was rushed onto the Sauber at the second race when McLaren have supposedly been examining the use of this system for two years.

Therefore don't think the team 'stall' is necessarily wrong in Sauber's case, even if the term itself is technically incorrect. If that makes sense.