Explain This please

[PlatinumZealot]

The big box structure under the floor.. It's the first time I am seen it so openly. I never realised how close to the ground it is..

This is Kubica @ SAT qualifying in Aus 09.

What are the mechanics behind running it so close to the floor? I am pondering about the flow of air under this thing..

[ISLAMATRON]

think thats what they call the reference plane.... the FIA legality plank is on it... they usually arent that low... maybe the tires are cold and thus pressures are low, plus some fuel on board

Any air underneath it creates ground effect downforce, and to either side feeds to the diffuser.

[ernos5]

well since it's qualifying, they probably lower the car and put stress on all parts of the car, run everything to the maximum to achieve a faster time, during the race we'll probably see it higher.

[ISLAMATRON]

well since it's qualifying, they probably lower the car and put stress on all parts of the car, run everything to the maximum to achieve a faster time, during the race we'll probably see it higher.

parc ferme remember? as you qual is as you race, unless you mean tire pressures

[PlatinumZealot]

think thats what they call the reference plane.... the FIA legality plank is on it... they usually arent that low... maybe the tires are cold and thus pressures are low, plus some fuel on board

Any air underneath it creates ground effect downforce, and to either side feeds to the diffuser.

This is what is puzzling me.. I wanted to hear how the closeness of it to the ground affects the down force. Do you think it is still operational at such low height? Even during a bottom out.

I was thinking about them pushing the air to the side too.. But with it this low, Do you think they want ALL the air IDEALLY to side and None directly under that plank?

[Crystalix]

The problem is, a very low underbody will increase sticky rubbing (between air and ground) and thus drag, but it won't give any advantage in downforce.
The optimal height is when the separation between car and ground "boundaries layers" is equal to zero.

[kilcoo316]

[quote="n smikle"This is what is puzzling me.. I wanted to hear how the closeness of it to the ground affects the down force.[/quote]

Well... put simply, the air pressure in that region (between car and track) is defined by the ambient static pressure [Ps] minus the dynamic pressure [Pd] (Bernoulli = 0.5 * density * velocity^2).


So, you've Ps-Pd acting on the car floor, but Ps acting on the upper surfaces of the car.


Hence its pushed into the ground.

[ISLAMATRON]

think thats what they call the reference plane.... the FIA legality plank is on it... they usually arent that low... maybe the tires are cold and thus pressures are low, plus some fuel on board

Any air underneath it creates ground effect downforce, and to either side feeds to the diffuser.

This is what is puzzling me.. I wanted to hear how the closeness of it to the ground affects the down force. Do you think it is still operational at such low height? Even during a bottom out.

I was thinking about them pushing the air to the side too.. But with it this low, Do you think they want ALL the air IDEALLY to side and None directly under that plank?

Really cool experiment, take 2 smooth sided glasses(perfectly round or so) and put them together under the faucet and let the water run between them. you'll see that they draw cloer together, and will do so even stronger as they get closer... until they touch! BERnouli's Law in action!

[xpensive]

kilcoo, don't you have Ps-Pd on top of the car as well, only the air-speed is slower and thus Pd is less, correct?

[PlatinumZealot]

The problem is, a very low underbody will increase sticky rubbing (between air and ground) and thus drag, but it won't give any advantage in downforce.
The optimal height is when the separation between car and ground "boundaries layers" is equal to zero.

=D> =D>

This is the kind of answer!

Thanks to all who replied however.

[humble sabot]

also remember that at speed the suspension compresses as the downforce piles on. You'll notice as well if you watch them from the side in a slower section the great deal of rake of the car, the flat bottom, isn't so level, and here we're seeing the front end at its legal lowest. If it ran this low a significant portion of the course the car would be disqualified as the legality plank would wear a great deal. The whole point of the plank, if you remember is to prevent the cars running too low.

[xpensive]

If you behold an air-stream separated by an object such as a wing-profile, or an F1 side-pod, this is what happens:

Total pressure-pt, is static pressure-ps plus dynamic pressure-pd. Then if total pressure is held constant:
ps1 + pd1 = ps2 + pd2
The above gives a static pressure differential, ps1 - ps2 (which creates Force), equal to pd2 - pd1.

When pd is density * speed squared / 2 and Force is static pressure differential times Area, the resulting force is:
area * density * (speed2^2 - speed1^2)/2.

This force can be substantial, if you can arrange the speed under the car to be 100 m/s, while the speed on top is only 60, downforce would be almost 4000 N per square-meter.

[kilcoo316]

kilcoo, don't you have Ps-Pd on top of the car as well, only the air-speed is slower and thus Pd is less, correct?

I really am writing half-assed posts these days!!!