Reducing the drag of a two element wing through stall

[ringo]

Yes the slot is what you say it is. Slot gap optimization is whole other science all together.

I realized how bad my wing was, I changed it by adding another element lower to the base of the wing to let some flow in. The flow attached then.
It's hard to set up the F1 style 2 element to keep the flow attached at the curved end part. Most of these wings are designed by programs, from parameters. It's an iterative process, so it's very difficult for to get it right by hand.

But yeah that example was just a demonstration of the concept. The upper element had attached flow so it would be similar case for the slit on the MP4. The bottom element is the more difficult, but flap blowing from the middle of the upper element for down-force wont make much off a difference. The slot is where the magic happens, which you said.

Because of this, I am leaning towards the idea of wake control to reduce drag by blowing from the middle the element, or what they call "base bleeding" which is not like the typical blown flap.

Other than that, I don't know why the FIA banned 3 element wings, they are less sensitive. The 2 element is more challenging and easier to separate, and i guess that is why teams are using flow vis to double check.
That curve near the trailing edge is the challenge. Where you see the temp sensor.



The flow vis looks magical to me now

[Tim.Wright]

If it is it will be the first time they have taken airflow in yaw into account.
Most designers still think the cars run strait all the time.

Im pretty sure this has been looked at for a few years already. I recall seeing the BMW Sauber wind tunnel in a documentry a few years ago. They could place the car in at different yaw angles.

I always thought that was what the shark fin was for.

Tim

[ringo]

Have you seen Scarbs interpretation? http://scarbsf1.wordpress.com/2010/02/1 ... shark-fin/

He suggests that the opening near the airbox not only cools oil, but is tunneled within the bulbous sharkfin and on to the rear wing. The air acts to seperate the fins further, creating a 'third element' - allowing for increased angle without stall.

That oil cooler business was my interpretation. I put it in the MP4 25 thread. It's on a pretty ugly drawing going around
I don't have a problem with the drawing being used, though i was surprised to see it on other message boards.
It all stemmed from the dead zone argument initially, if i had know i would have drawn it better.

[autogyro]

If it is it will be the first time they have taken airflow in yaw into account.
Most designers still think the cars run strait all the time.

Im pretty sure this has been looked at for a few years already. I recall seeing the BMW Sauber wind tunnel in a documentry a few years ago. They could place the car in at different yaw angles.

I always thought that was what the shark fin was for.

Tim

The effects of yaw on a design have been looked at over the whole history of racing. What I am sayin is that this is after the initial design is done and fins are then in effect a repair job for a 'strait line' design.

[McMacca]

Guys, First I have been following this for some time now and I think we have missed the point of "stalling" the wing. Stalling is not to reduce the drag of the wing but to remove the downforce it creates

Wing creates downforce - more speed = more downforce
when do you want minimum downforce - at high speed?
If the wing is stalled, regardless of the drag, it produces no (or comparatively little) downforce, thus reducing? The Rolling resistance of the rear wheels (driven axle) giving, in theory a higher top speed.

Examples - Honda f1 land speed attempt a couple of years ago had NO rear wing at all.
Veyron - Retracts its rear wing in High Speed Mode......

Unless of course the drag of a stalled wing cancels out the reduced downforce then this is a null point.

But the big question is, why feed air to the wing, to control the stall point? basic aerodynamics say this is achieved by change of AOA. So if the wing is fixed can the amount of air "blown" onto the wing create significant change in stall speed of the wing?

Is this what Macca are up to?

Maybe the more educated members could provide some rough numbers, eg drag co-efficent of a stalled wing vs non stalled wing, amount of downforce produced prior and after stall etc?

(feel free to flame if I'm miles off! )

[f1ar]

If it is it will be the first time they have taken airflow in yaw into account.
Most designers still think the cars run strait all the time.

Im pretty sure this has been looked at for a few years already. I recall seeing the BMW Sauber wind tunnel in a documentry a few years ago. They could place the car in at different yaw angles.

I always thought that was what the shark fin was for.

Tim

The effects of yaw on a design have been looked at over the whole history of racing. What I am sayin is that this is after the initial design is done and fins are then in effect a repair job for a 'strait line' design.

Can´t wait for F1eng to reply your affirmations

The effects of yaw in F1 aerodynamics is being studied since a long time ago, in fact you can check the specs of several F1 wind tunnels, most of them allows 5-10º variation in yaw. There are also several F1 cfd images around the web showing the cars tested under the same conditions. I can´t in my narrow mind even think of such a team as Mclaren adding a fin as a 'repair job', heck it´s hard to think even usf1 would do such thing (if the car was ever built that is).

[autogyro]

Surely anything over 10 degrees of yaw will negate almost all of the aerodynamic benefit on the current cars, fin or no fin?
Much more efficient flying down a wing on landing a Tiger Moth at 30 degrees of yaw and much more fun.
F1eng?

[myurr]

Been thinking about the whole engine cover thing and was wondering if there was indeed a power source in that region that could be legally used to power / drive or control the effect. I haven't read through the whole thread yet, but has anyone considered the acoustic effects of the engine at the base of that chamber?

Could they use resonance or similar to effectively move or control air within the chamber?

[segedunum]

Could they use resonance or similar to effectively move or control air within the chamber?

You've got to be kidding? I thought I'd seen it all on this topic.

[Pup]

I think that's probably part of it, though I doubt there'd be enough change in rolling resistance to counter the extra drag. But it can't hurt. I still think the key is in the reduced induced drag.

One other, sort of related thing is this - if the rear wing is unloaded, the rear of the car will rise, meaning a more steeply sloped and therefore more effective floor and diffuser, which are relatively drag free. So perhaps they're gaining back a bit of downforce there, helping to stabilize the car and aid in braking at the end of the straight.

[horse]

Ok, guys, sorry this isn't the worlds greatest drawing. Top diagram shows how I would expect the stream lines to be in normal operation. Bottom diagram shows injecting against the flow. Normally this would be very bad as it would stall the whole wing and makes lots of drag. My idea though, is that some flow coming from lower down reattaches the flow towards the trailing edge. Thus, only the leading edge of the wing is stalled (the bit doing most of the work) and the rest of the wing works normally. If such a "magic flow" from below existed it would trap the circulating flow (with some bleeding into the magic flow) keeping the flow nice and tidy behind the wing and thus not making too much drag. This may match up with the flow-viz that could show a detached area and then re-attached flow.

Criticisms, please?

[Pup]

I think what you've drawn is essentially a laminar bubble. Better than a full stall, but draggier than a fully laminar flow. But I don't think F1 wings have laminar flow, so something similar to what you've drawn probably exists even in normal operation.

But here's a question for you - if you think it would be better to create a bubble like you've drawn, which means less DF and more drag, then why not take the next step for a full stall? Come on, horse - join the dark side.

See here: Laminar Bubbles for Dummies, Like Me.

[horse]

I think what you've drawn is essentially a laminar bubble. Better than a full stall, but draggier than a fully laminar flow. But I don't think F1 wings have laminar flow, so something similar to what you've drawn probably exists even in normal operation.

See here: Laminar Bubbles for Dummies, Like Me.

Thanks, Pup. I'll have a look at that. I'm well out of my depth, I know, but I thought it might be a possibility. My feeling was that they must be aerodynamic surfaces to some extent, otherwise, why not just use flat plates?

But here's a question for you - if you think it would be better to create a bubble like you've drawn, which means less DF and more drag, then why not take the next step for a full stall? Come on, horse - join the dark side.

The reason I thought that a focused stall might be more effective was that the lower portion of the element is less vertical so perhaps a stall there would be less detrimental than at the top where the flap is near vertical.

Anyway, I shall now step away from the breach before I make a proper twit of myself.

[ringo]

Stalling with wake control is how the angle of attacked can be changed.
Remember the down-force is really created by changing the momentum of the air. In the up-wash the air is directed upward so the reaction force is downward pushing the wing down.
The wake is the main indicator of the angle of attack, the chord line is really just a geometric reference.

If the wake is pulled downward (just imagine a shorter rooster tail in the rain) The pressure drag, down-force and Angle of attack will be reduced.

Wake control is also used in the military on supersonic missiles, where drag at those speeds is even more critical.

Links on base bleeding:

http://mechanical.rutgers.edu/iutam/th5.pdf

http://biblioteca.universia.net/html_bu ... 03486.html

It has also been mentioned years ago on this forum it seems. Looks like the FXX and f430 use it too.
viewtopic.php?f=11&t=4490&start=45

Aerodynamic channels both fore and in the midsection are fitted with adjustable flaps that control the airflow. When road speed exceeds 150 mph, the midsection flaps achieve a "base bleed," diverting flow into channels that exit on the car’s rearmost surface, just below the twin exhaust outlets on either side.

This achieves several goals: It trades away a bit of unnecessary downforce and concomitant drag. And it reduces drag further by beneficially affecting the car’s wake, that inherently low-pressure region being dragged along at the rear. Flow from the four exhaust outlets also contributes to this wake drag reduction. (Ferrari’s F1 cars used exhaust flow in a similarly beneficial manner, their goal being to optimize flow over the rear wing elements.) Last, smallish winglets atop the rear flanks of the FXX fine-tune the wake control.

Didn't one of the Ferrari road car engineers come over to Mclaren last year??

[horse]

Links on base bleeding:

http://mechanical.rutgers.edu/iutam/th5.pdf

http://biblioteca.universia.net/html_bu ... 03486.html

I'm hearing the wake control, Ringo, but is a F1 rear wing really like a circular cylinder? This is a serious question, because if it is then your 100% right. I think base bleeding works because it "fills the gaps" created by stalled flow, such as behind a cylinder or a car. However, if the wing does work like an aerodynamic surface, then, unless it's always in stall anyway, is base bleeding as beneficial?

Do you have any link to show base bleeding used for an aerofoil?

EDIT: Oh, hang on! Stall the wing somehow, say with some airflow from below at high speed, then bleed into it to remove the damage of doing so. Have I seen the light???