Reducing the drag of a two element wing through stall

[Shaddock]

I was thinking about the idea of controlling the air from the snorkel, and it made me think back to when a friend of mine used to work balancing air conditioning systems in conference centres, and this got me thinking…

You don’t need a driver input!

What you do is ‘tune’ or control the air the snorkel can provide to the ‘Chamber’ at C via the shape, size of the external aperture) of the snorkel (McLaren have already tested this) or fit an internal air restrictor.

If the fastest corner of a track is say 130mph then you add a little for safety, say 140mph, and you work out what air pressure is required at C to create the switch, and tune the snorkel accordingly.

As the cars accelerate past 140mph enough pressure is provided by the snorkel at C to switch the flows exit path, and stall the rear wing or for the real conspiracy theorists the diffuser as well!

No driver input required, and the system is calibrated for each track.

[Pup]

Hi guys,

I thought I might to have a go at explaining what I think is happening. I think it very much relies on there being two elements to the wing. To illustrate, consider the two element wing, operating not in stall:



My idea here is that the two elements have a combined chord line, which produces a steep angle of attack. Hence, the forces generated by the wing combine to produce both down force and drag. Now consider the situation where only the top element is in stall:



Here, the elements can be considered separately. We see the force vector of the main element is producing mostly DF and the flap in stall is producing mostly drag. I think the argument goes that because the flap is small compared to the main element, then the combined drag of this system will be less than the drag from the wing operating as one seen in the first figure. That's my guess anyway.

Please note that the length of the vectors are just for illustration.

Please be nice.

I would only suggest that the main element probably has a steeper AoA than you've shown, particularly on the McLaren. And we'd also have to consider that the airflow at the back of the car probably moving a bit downward as well, effectively increasing the AoA of the whole thing even more.

[forty-two]

I was thinking about the idea of controlling the air from the snorkel, and it made me think back to when a friend of mine used to work balancing air conditioning systems in conference centres, and this got me thinking…

You don’t need a driver input!

What you do is ‘tune’ or control the air the snorkel can provide to the ‘Chamber’ at C via the shape, size of the external aperture) of the snorkel (McLaren have already tested this) or fit an internal air restrictor.

If the fastest corner of a track is say 130mph then you add a little for safety, say 140mph, and you work out what air pressure is required at C to create the switch, and tune the snorkel accordingly.

As the cars accelerate past 140mph enough pressure is provided by the snorkel at C to switch the flows exit path, and stall the rear wing or for the real conspiracy theorists the diffuser as well!

No driver input required, and the system is calibrated for each track.

Sounds feasible to me!

[Pup]

Who said DEADZONE? (again)

Yes, please use the proper terminology, I believe within the team it is referred to as a "goony device".

[astracrazy]

seems a good idea, more sensible than the driver using there knee...

[feynman]

But such a "passive" version wouldn't require a snorkel, you could have the switching inlet/input anywhere, just stick the calibrated inlet up in the free-air beside the oil cooler inlet, right beside the switching mechanism.

There must be a quite specific set of reasons why such an auxillary input isn't up and out of the way, and instead has to be down at the cockpit, just above the pedal box.

[Astro1]

McLaren "We're very confident that our car is entirely legal, and we're not aware of any protest. In fact, we've spoken to Ferrari this morning and they're not aware of any protest either."

http://www.pitpass.com/fes_php/pitpass_ ... t_id=40054

[horse]

In fact, we've spoken to Ferrari this morning and they're not aware of any protest either."

Is that CH making stuff up then, or has he just opened his mouth too soon?

[Roger the knife]

In fact, we've spoken to Ferrari this morning and they're not aware of any protest either."

Is that CH making stuff up then, or has he just opened his mouth too soon?

Sounds like CH pretending to be Gordon Brown and just beating around the bush

[Hangaku]

Perhaps the statement from McLaren is just very well prepared. They've said that Ferrari aren't aware of any protest. It doesn't mean that Ferrari haven't request clarification from the FIA. Clarification != Protest

[horse]

I would only suggest that the main element probably has a steeper AoA than you've shown, particularly on the McLaren

Yeah, I was looking at the main element, and it's interesting. It looks quite long from the top and kind of cupped. I suppose the mean chamber line must be quite far from the chord line.

And we'd also have to consider that the airflow at the back of the car probably moving a bit downward as well, effectively increasing the AoA of the whole thing even more.

I agree that the airflow around the wing is also of interest, not just because of the airflow being drawn down into the wing, but also the effect of the up-draft from the diffuser on the flow behind it.

[Shaddock]

But such a "passive" version wouldn't require a snorkel, you could have the switching inlet/input anywhere, just stick the calibrated inlet up in the free-air beside the oil cooler inlet, right beside the switching mechanism.

There must be a quite specific set of reasons why such an auxillary input isn't up and out of the way, and instead has to be down at the cockpit, just above the pedal box.

I'd thought of this and it's a good point. The only explanations I can offer is that aerodynamically in its current location its ‘out of the way’.

With or without the snorkel, air passing over the top of the car hits the driver, and its smooth flow is disrupted. Drop the snorkel on the airbox and you have to start thinking about losses to the rear wing.

The other idea is if there is an internal air restrictor this could still be operated by the driver to give more than one speed the switch can operate at.

[simoncm]

Ok, first post on this forum (interesting topic though). Thought I'd get a bit heavy with the maths (degree in theoretical physics and all that).

Now, [-o< , this is a first approx, really only to show that turbulent flow (stalled rearward wing) CAN have less overall drag on the car. Please, be nice, I fully realize the limitations of these calculations. (For example, the lift will not be perpendicular to the chord of the wing, but will be approx 10 degrees off due to the AoA of the wing in the air flow) - however I'm ignoring this for a first approx).

Assume the rearward wing has a nice laminar flow etc...

The lift of the wing (approx perpendicular to the chord) is:
1/2 * Cl * (rho) * V^2 * A
where: Cl is lift coefficient, A is wing area, (rho) is air density, and V is air velocity

The total backward force of the wing having a laminar flow is:
D * cos(theta) + L * sin(theta)
where (theta) is the angle of the wing (NOT angle of attack to the airflow, which is affected by the forward wing bending the airflow upward), L is lift perpendicular to the chord of the wing, D is drag parallel to the chord of the wing.

Assume D is small (first approximation etc...)

Therefore the backward force due to the wing is
1/2 * Cl * (rho) * V^2 * A * sin(theta)

Now assume the rearward wing is not in a laminar flow and is acting more like a brick/flat plate/whatever, with turbulent flow behind it.

Rearward drag is now:
1/2 * Cd * (rho) * V^2 * A'
where A' is the forward facing area of the wing, A' = A * sin(theta)

Therefore the rearward drag in turbulent flow is
1/2 * Cd * (rho) * V^2 * A * sin(theta)

Everything cancels nicely, therefore the ratio of the drags is
Cl/Cd

A reasonable Cl is 1.5, an angled plate in an air flow has a Cd of 0.5 to 0.8

Therefore the "drag" due to the wing generating downforce is greater (ratio > 1) than the "drag" due to the wing being stalled. In this case by a factor of 2.

[nacho]

Wouldn't it be nice to blow a part of the exhaust gases to the rear wing?

[mike_dangerous]

Wouldn't it be nice to blow a part of the exhaust gases to the rear wing?

Would the exhaust not contain some water vapour which could condense on the wing or even oil particles? That could be detrimental couldn't it?