14 replies to this topic

[Buttoneer]

Yes sorry to bring a RC subject here but this is related to the Barrichello overtake on Schumacher at the Hungaroring last weekend.

There's a good image here for those who have not seen it; http://www.jamesalle...ns3-800x524.jpg

My question relates to the effect of the turbulent air along the side of the car in that situation. It must be something Indycar has grappled with over the years but would there be any sort of 'ground effect' equivalent that will either serve to suck the car towards the wall or even an opposite effect which tries to push away?

I find it hard to believe there was no effect at all since we know the outwash front wings are designed to create specific airflows around the car and tyres and this air must go somewhere.

Just how well did Rubens do to avoid losing control?

[Tony Matthews]

http://www.jamesalle...ns3-800x524.jpg

Great photo - my instant thought was that he was brushing the wall, but in fact, if you look at the shadow cast by the front wheels, RB is already past the end of the wall, by about 25 - 30% car length. Certainly the front wheel is well past the end. As to possible venturi effect, an interesting question. I notice that when I'm walking back from the pub, if I walk close to a wall there is an inevitable slight contact...

[Buttoneer]

That's possibly still due to the ground effect - it keeps swirling around under your feet when you look down.

[mariner]

Two thoughts

In Jackie Stewarts biography he tells how , on his first race at Indy in 1966 Jim Clark explained to him that to go fast at Indy you had to get the car so close to the wall that you could clearly see the shadow of the wheels on the wall. As Clark had won the '65 race and Stewart nearly won the '66 race it sounds like good advice.

Secondly the events last weekend with flexible wings and Mr Schumacher made me think again about the " flatten the rear wing to pass" system planned for next year. The car is at max. speed on the straight with the front wing flexing down to the ground when suddenly the driver gets the "green to pass" light from race control and flattens the rear wing.

Result - the rear rises up on the springs/tyre springs , that increases rake angle and so the front wing attack angle. As the front wing is well ahead of the front wheels the rake change moves it even closer to ground all of which, I think, increases front grip and reduces relative rear grip.

Now Mr Sch., or whomever is being overtaken, tries a banzai blocking swerve as nothing else can prevent being passed and the overtaking car has to manoveure violently to avoid a collision. Will it have enough stabilty to do that safely or will the excess of front end aero versus rear aero load cause it to go out of control.

I am not enough of a dynamics expert to know but you do not usually change the whole front/rear balance of a car without stability consequences and the scenario above will probably happen at 300kph just before the braking point so it is worth thinking about.

Seeing how close the two cars were I hope the F1 technical guru's are running this kind of check before agreeing to the rear wing flattening idea.

[primer]

Just how well did Rubens do to avoid losing control?

For him the biggest danger was contact with MS' car, and he did alright in avoiding that. Any aerodynamic suckage towards wall (and theoretically speaking there might be some, momentarily, as his car came closest to wall) would be barely felt through the steering wheel both because of the short period of time he was close enough to the wall, and also because this component would be so small that aerodynamic downforce would continue to dominate the handling.

The sides of the car are nowhere as optimized for 'sideforce' as the floor is for downforce. And I am not sure whether he came close enough to the walls for their to be any measurable change, he would have to come within less than half an inch of the wall for us to consider the aero effects seriously.

Edit: As a matter of fact, there might be no suckage towards the wall at all because the two closest surfaces would be the two tires. These are rotating and creating turbulence, and in the middle you have an aperture out of which comes air used to cool brakes. Located in between these two chaotic airstreams, the sidewalls of tires would barely provide any usable area to generate any aero force towards the wall no matter how close they came to the wall.

Edited by primer, 05 August 2010 - 10:23.

[munks]

I thought driving close to a wall was basically equivalent to driving next to an identical car. Are they sucked together or pushed apart?

[primer]

Are they sucked together or pushed apart?

If there is sufficient venturi effect the car will be pulled towards the wall. But I doubt there was any meaningful amount, and Rubens also had Schumacher on his other side to balance everything out!

Schumacher would never swerve like a madman and put another driver's life in danger. As a matter of fact, by driving so close to Schumacher Rubens created a venturi effect between their cars, and pulled Schumacher towards the wall with him. Ban Rubens!

I am being so silly!

Edited by primer, 05 August 2010 - 16:38.

[cheapracer]

Yes sorry to bring a RC subject here but this is related to the Barrichello overtake on Schumacher at the Hungaroring last weekend.

Looks like a tech question to me :-)

If anything Rubens would have more downforce as the air has no where to go to the sides, only up and over/under the car.

Primer, the tits were better.

Edited by cheapracer, 06 August 2010 - 03:54.

[J. Edlund]

Secondly the events last weekend with flexible wings and Mr Schumacher made me think again about the " flatten the rear wing to pass" system planned for next year. The car is at max. speed on the straight with the front wing flexing down to the ground when suddenly the driver gets the "green to pass" light from race control and flattens the rear wing.

Result - the rear rises up on the springs/tyre springs , that increases rake angle and so the front wing attack angle. As the front wing is well ahead of the front wheels the rake change moves it even closer to ground all of which, I think, increases front grip and reduces relative rear grip.

This situation nex year can't be significantly different to the current system with the F-duct, which also decrease rear wing downforce in turn for less drag.

[PNSD]

An interesting question... a rumour in 2007 was that one of the reasons the Honda RA107 wasnt great was because they used a full scale car but it happened to be too close to the sidewalls of the tunnel, and so when using a 60% model the results were off...
I thought an area of low pressure built up which if you got too close simply sucked you in... but I dont know. A simple CFD run with a simple car might be worth a try.

[Paolo]

I thought I had the answer: a moving body near a surface gets a "mirror effect"; that is the airflow around it is about the same as the one caused by two identical objects moving abreast.
The "about" is due to the fact that the mirror effect doesn't account for boundary layers.
So, a car near a wall should meet more drag , and be sucked towards the wall.

Yet my faith in this was recently shaken, as I read (cannot remember where) a Nascar tech report stating the opposite was true, and they had the measurement to prove it.
So Clark might have been right.

[jatwarks]

Given that F1 cars are supposed to be so aerodynamically critical, then I would have thought that some effect must be felt when running close to a wall, if only from reflected airflow from the wall.

The front tyres cause quite a lot of turbulence anyway, so it’s hard to see too much happening due to the presence of the wall. The reflected air may have the same effect as the F-duct in disturbing airflow over the rear wing; even if the car isn't able to reach a higher speed, I bet the presence of the wall makes the driver think he's going much faster!

Two ships passing too closely at sea will be drawn together by the fact that the surface area of sea between them is smaller and so the water pressure on the hulls pushes them together: That doesn't apply in this case because of the much lower density of air.

[Buttoneer]

@jatwarks, interesting point about the ships - this is an issue for ship-ship refuelling isn't it? With respect to F1, most of the cars this year have employed outwash front wings which I thought might have the opposite effect and send a larger body of air towards the wall which might force the two bodies apart.

[ivanalesi]

In Jackie Stewarts biography he tells how , on his first race at Indy in 1966 Jim Clark explained to him that to go fast at Indy you had to get the car so close to the wall that you could clearly see the shadow of the wheels on the wall. As Clark had won the '65 race and Stewart nearly won the '66 race it sounds like good advice.

I guess Clark meant that you've got to exit the corners this close to the wall! You can watch some onboards from Indycar nowadays and drivers always move out of the wall as soon as they exit the corner with the most speed. Then while they travel on the straight part, they are getting away from the wall until they have to enter the next corner when they move close to the wall in order to enter with a wider corner angle.
I think most F1 drivers were doing the same at Indy. Also I think static walls are a problem for all wind-tunnels, because at the end of the day the wall only moves along with the car when it get a very big push from the car itself:)))

Check this out how far from the wall and near to the grass Dario gets:

[FrankB]

Two ships passing too closely at sea will be drawn together by the fact that the surface area of sea between them is smaller and so the water pressure on the hulls pushes them together: That doesn't apply in this case because of the much lower density of air.

Why would the smaller surface area of the sea between two ships cause a reduction in water pressure? Isn't it more likely that the amount of water passing between the bows of the two ships then has to pass between the two ships at their widest point - a venturi effect resulting in pressure reduction.