Question about disturbed air

[Culpan]

I know that as a F1 car travels through the air it disrupts it (as we have seen in the fantastic CFD Thread) and the commentators on ITV often refer to it as "Dirty Air" which I think affects the aerodynamic performance of the car slightly; but also they refer to "Slingshoting" when a car gets close behind another car, and I think because of the reduced air resistance it goes faster and "slingshots" round the car.

My question is will a designer take into account the possibility of their car being over taken in this way and do they (or could they) alter the rear wing for example to change the way the air moves over it or around it to hinder a car trying to overtake through Slingshoting; and what affect does this "Dirty air have on the cars"

[joseff]

I don't know the answer to that question, but I remember Paul Van Valkenburgh wrote quite a few years ago that it's actually possible to design a front wing in such a way to disrupt the diffuser of the car in front!

[NickT]

Ok this doesn't relate directly to F1.

I remember watching an open wheel oval race late one night/early one morning. The commentators were saying that if two cars run very close together on the oval, the lead car could actually run faster than if running on its own. Obviously the trailing car could run faster to as it was slipstreaming. Sure enough the two leaders worked together for a number of laps and pulled out an appreciable lead.

Does anyone have any idea what is going on in this situation?

[KeithYoung]

yes it can aid cars behind on straights, but you also must realise it will ruin the air going over the front wing, and the whole car in general. you will hear all the time that drivers cant get past in the corners because everytime they get close they lose alot of their downforce.

think of driving down the highway, when i want gorgeose gas mileage i find a semi that is speeding and just tailgate it until my exit, my car doesnt have to overcome as much drag force, therefore my engine doesnt have to work as hard to attain the same speed, same basic rule applies for F1.

[Monstrobolaxa]

What everyone is talking about is the slip-stream. When a car passes through air it a "hole" in the air...the air pressure in this hole is close to zero....this means that there aren't any particles of air.

Air resistance is caused by friction of air particles on a body. So if you take the air particles and put another body in that hole it won't have any drag....the problem is that if you are behind another car and there aren't enough air particles hitting your wing....your acr won't be creating downforce, cause down force is caused by the diference of air pressure from one side of the wing to the other side of the wing. So if the pressure on top of the wing is zero and on the bottom it's also zero you won't have any downforce....but in a straight line it's an advantage cause if you don't hqave air particles hitting the wing you won't have drag....this will cause an increase in you straight line speed.

Try finding an onboard kimi raikonen video online at the USA GP 2003, there's one time where he slipstreams the car in front...and you can hear a increase of the revs....when he leaves the slip stream you hear the loss of revs due to the increase of drag.

[Monstrobolaxa]

What everyone is talking about is the slip-stream. When a car passes through air it a "hole" in the air...the air pressure in this hole is close to zero....this means that there aren't any particles of air.

Air resistance is caused by friction of air particles on a body. So if you take the air particles and put another body in that hole it won't have any drag....the problem is that if you are behind another car and there aren't enough air particles hitting your wing....your acr won't be creating downforce, cause down force is caused by the diference of air pressure from one side of the wing to the other side of the wing. So if the pressure on top of the wing is zero and on the bottom it's also zero you won't have any downforce....but in a straight line it's an advantage cause if you don't hqave air particles hitting the wing you won't have drag....this will cause an increase in you straight line speed.

Try finding an onboard kimi raikonen video online at the USA GP 2003, there's one time where he slipstreams the car in front...and you can hear a increase of the revs....when he leaves the slip stream you hear the loss of revs due to the increase of drag.

[NickT]

Yes, I understood the slip streaming details before posting the question.

The commentators were saying that if two cars run very close together on the oval, the lead car could actually run faster than if running on its own.

What I really wanted to know was why does having a car following you, very closely on an oval, increase your top speed?

[Skjar]

Well, because when you are running on your own (nobody is behind you), you have lower air pressure behind you. And this suck you back. But if you have somebody behind you, lower air pressure will suck him back. Between you and him is a normal air pressure, because the air between cars won't mix with air streaming around cars. That is my explanation.

[SKRAT]

The slipstreaming strategy can be seen the north american stock car series because their aero is so bad. You'll see trains of 3+ cars and any car that gets off the train immediately falls behind unless there are other cars able to form another slipstream train. (Also sort of similar to the peleton strategy in bicycle racing).

Anyway, the FRONT car is also able to go faster because of reduced aerodynamic drag and hence more available engine power. The following car takes the airflow off the the lead car and reduces somewhat the low pressure in the back of the lead car. So now the front and rear drag are split between the two cars (or X cars in a slipstream train) making more engine power available.

The rear car still has the better of it, but the front car gets at least some benefit. This seems to work better straightaway, bunched racing like Nascar and LeTour de France than on F1 road courses.

Hope this helps,
Paul C

[Monstrobolaxa]

very simple to answer: the car infront of you is opening a hole in the air and you are running in it....so you don't have any drag pulling you back.

[Mclaren11]

In response to the origonal question I do remember hearing once that a designer made special trailing edges for the wing on the back of his car that helped to minimise the advantage on the car in back. I cannot however remember whitch car or when it was.

Also I remember seeing a picture of an arrows car with the front wing high up out of the "Dirty air" about 1.5 meters up off of the nose. I assume this was to continue to gain the effects of the slipstream without loosing downforce from the front wing

[Mclaren11]

In response to the origonal question I do remember hearing once that a designer made special trailing edges for the wing on the back of his car that helped to minimise the advantage on the car in back. I cannot however remember whitch car or when it was.

Also I remember seeing a picture of an arrows car with the front wing high up out of the "Dirty air" about 1.5 meters up off of the nose. I assume this was to continue to gain the effects of the slipstream without loosing downforce from the front wing

[NickT]

Thanks guys, it all makes sense now.

Cheers

NickT

[Guest]

The front of a second car can also destroy the downforce of a leading car.
I have seen that on a NASCAR race. Two cars run as close together until the first car has lost downforce at the rear and the control of the car.
The second car has not touched the first only the air blader in front has destroyed the downforce.
This phanomen is used by the Spliter.

[joseff]

Recall also the infamous "Hanford device" used in CART.

Its purpose is to create zero lift, huge amounts of drag, and hence produce lots of slipstreaming in oval events.