6 replies to this topic

[Greg Locock]

I've run into a dead end here, but I'm sure someone knows the answer.

Lapsim allows an entry for variation of drag and lift coefficient against ride height - I've got a curve for a a front wing, just wondered if (for example) Peter Wright's book has more details?

Conceptually I'd like to split it up into a model that separates front wing, rear wing, and floor (ground effect), contributions.

While I'm at it, is 5 a reasonable approximations for the L/D for the wings? how about the ground effect?

here's my front wing data, c=chord=223 mm, h is height off the ground

It pretty much obeys CL^3.5*h=constant - I don't know why, exactly, obviously there is some effect with the stream velocity.

Front wing

h/c CL h mm
0.67 0.83 149.41
0.45 0.92 100.35
0.31 1.04 69.13
0.2 1.2 44.6
0.1 1.39 22.3

[wegmann]

5 may be a reasonable L/D for the front wing, but the rear wing tends to be quite a bit lower (possibly due to the dirty air?). Ground effect is pretty efficient, especially since lowering the car creates less drag and more downforce.

Are you talking about an F1 car, and what exactly are you looking for? Numbers?

The rake is an important factor. A lower ride height in the front tends to give more downforce, but does increase drag. A lower ride height in the rear gives less downforce AND more drag. Equal ride heights tends to cause the least drag, but the downforce is medium.

[Greg Locock]

Yes, F1, and yes, numbers.

Actually I've discovered that the freebie edition of lapsim does not use these tables, so it is of academic interest only now.

[wegmann]

These numbers are approximate for 2002 cars at medium downforce (and are fairly accurate relative to each other), and you can expect 2003 cars to have roughly the same drag and probably 10% more downforce.

At 30mm front ride height, 35mm rear ride height, you'll get around Cl=-2.760 and Cd=0.990.
At 10mm front ride height, 15mm rear ride height, you'll get around Cl=-2.830 and Cd=0.975.

The frontal area is normally around 1.4 m^2, but can probably go as low as 1.2 m^2 for Monza, if this info is useful to you.

[Chan]

Originally posted by wegmann
These numbers are approximate for 2002 cars at medium downforce (and are fairly accurate relative to each other), and you can expect 2003 cars to have roughly the same drag and probably 10% more downforce.

At 30mm front ride height, 35mm rear ride height, you'll get around Cl=-2.760 and Cd=0.990.
At 10mm front ride height, 15mm rear ride height, you'll get around Cl=-2.830 and Cd=0.975.

The frontal area is normally around 1.4 m^2, but can probably go as low as 1.2 m^2 for Monza, if this info is useful to you.

Interesting figures, what's your source?

Efficiency is in the region of 2 for a high downforce rear wing and nearer to 3 for low downforce

I agree with you about the variation with ride height. Ideally you want a ride height map with small changes in aerodynamic balance for the cornering ride heights. Ride heights vary with circuit but a transition of 30mm to 20mm for front and 45mm to 30mm for rear is typical for cornering. You can expect the drag to drop by approx 2% during this transition and the lift to remain approx the same.

[wegmann]

The source is a combination of actual figures from an older F1 car (still in the stepped plank era, though) and some modern estimations. Cannot say more, but I agree with your statement about rear wing efficiency.

You are also correct about the overall drag and downforce. I should also note that the center of pressure will move around a bit. For example, the front wing efficiency will increase with proximity to the ground, so the CofP will move forward under braking. I don't know if that kind of thing is taken into account with LapSim.

[Greg Locock]

No, that is a subtlety it won't deal with. As I say, the freebie version doesn't even implement this table of lift and drag vs rideheight, so this is all moot, if interesting.