Cars NFS Tournament Class B 1.6

[Avo77]

I can add that having driven one 930targa (not so different from a 964) at high speed, the lift on the front was very evident in terms of steering load and response. Being the spoiler of the 964 (or 993) acting well outside the wheelbase, any downforce it generates would add even more lift on the front.

 

[Kyuubeey]

Flat undertray, side-trays work as a pseudo-splitter when combined with the opening and the whole thing is shaped like an airdam. Same concept on the MR2, and GT-R's have a real airdam too ala. Singer style front end, just combined with the splitter shape and trays on the R34.

Aerofoils aren't the only things which produce negative lift.

EDIT:

There's almost no similarities between a 930 and 964. They only share misc. parts, and the entire thing is completely different, from the suspension kinematics to the geometry of the tub and underbody to even how the springing and damping is conducted.

 

[Avo77]

Found this link with some references from a paper published by Manfred Harrer (head of Porsche chassis development). Car models are not listed but I think it refers to 911 base models (993 from 1994 to 1997).

Lift coefficients

The interesting part is the definition of front and rear lift coefficients that are calculated by taking into account only the pure lift components (as reasonable) obtained by isolating the load transfer contribution due to drag.

By using the data in the graph and considering the drag effect, the 993 at 200km/h would have something like 33kg of lift at the front and almost zero at the rear.

 

[Kyuubeey]

Thanks, I'll consider it for my own 911s. The CLs given there definitely coincide with my chart, so if the definition is that the lift is isolated, there really isn't that much to argue.

I believe the data either way, but I've had some doubts. I definitely think the cars should be more stable at 150+.

It's also not impossible to make slight downforce or very close to zero lift front without any obvious significant aero surfaces, especially if you don't have a big wing lifting the front. So I assumed these are values from wind tunnel testing, without any isolation of forces.

If the 964 had a positive AOA in the front portion, I'd believe pro-downforce more, but the AOA is negative, which is generally pro-lift, so front end lift is very much so possible and likely.

Hard data is something I believe more than "I think", so thanks for providing some. Now we can work off that.

 

[Avo77]

In the graph I posted the 964 has much more lift at the front than the 993...

 

[Kyuubeey]

In the graph I posted the 964 has much more lift at the front than the 993...

I mean, proportionally maybe, but it's like a few kilos...

Assuming CL1 is front.

 

[Avo77]

I mean, proportionally maybe, but it's like a few kilos...

Assuming CL1 is front.

Yes, Cl1 is front.
Comparing data from the graph and from the table the delta in aero balance is about 20kg more lift on the front at 200km/h.
Not huge in absolute terms but it's like having tires on the front with 3% less adherence and this makes a lot of difference.

 

[Kyuubeey]

Yes, Cl1 is front.
Comparing data from the graph and from the table the delta in aero balance is about 20kg more lift on the front at 200km/h.
Not huge in absolute terms but it's like having tires on the front with 3% less adherence and this makes a lot of difference.

You should go and recalculate your ****. I'm getting 6kg~ vs 4.5kg~ @ 200km/h.

 

[Avo77]

You should go and recalculate your ****. I'm getting 6kg~ vs 4.5kg~ @ 200km/h.

From the table the Cla for 964 is -0.01 so about -3,4kg of lift.
From the graph the Cla for 964 seems to be something like 0,03 so about 10,4kg of lift.

The difference is like 14kg of lift more (I did the calculation in mind and rounded too much but still...).

What am I missing?

 

[Kyuubeey]

From the table the Cla for 964 is -0.01 so about -3,4kg of lift.
From the graph the Cla for 964 seems to be something like 0,03 so about 10,4kg of lift.

The difference is like 14kg of lift more (I did the calculation in mind and rounded too much but still...).

What am I missing?

0.5 x 1.01325 x 1.0 x -0.0315 X 3085.8025 = -49.2453577842 N @ 200km/h @ sea-level

Or if you would like dynamic pressure:

48.6 ÷ ((0.5 × 55.55^2) × 1.0) = 0.0314990995

I think AC uses altitude and temp in aero, not sure.

I tested ingame, and I get *almost* these values, but not quite. Although we're talking about so low numbers here, it could simply be rounding inaccuracy in the app.

 

[Avo77]

You used unusual air density (probably that number is valid at 70deg Celsius...) and wrong area (the coefficients are calculated respect to frontal area).

You should go and recalculate your ****
Also changing your bad attitude would be beneficial in the meantime.

 

[Kyuubeey]

Density, fair enough. I rely on AC anyway, as we need to go by whatever pressure/temp combination AC says the car's at, and I don't know what pressure AC assumes/how anything scales. *shrug*.

However I've never heard of anyone *actually* calculating CL based on the car's frontal area .

Everything I've ever seen has A = 1. Could you confirm and show the section in the paper where it's stated that the A is the car's frontal area, and also the cited surface area?

 

[Avo77]

In car aerodynamics calculation everything is normalised respect to frontal area starting from 1886.
If you want a reference from the same book just look at page 65 in the link I posted.

 

[Kyuubeey]

In car aerodynamics calculation everything is normalised respect to frontal area starting from 1886.
If you want a reference from the same book just look at page 65 in the link I posted.

Do you actually work as an aerodynamic engineer, or perhaps an university professor? I don't, so I'm going to keep an open mind.

Hoever, I've never, ever heard of Cz actually being derived from anything but A = 1.000m^2. My experience pool doesn't begin from 1886 I suppose, so I'm willing to be proven wrong, but I personally have never ran into any paper where A isn't assumed to be 1.000m^2 for CD and CL values. I've always seen it mentioned if it changes from 1.0 to the real frontal surface area, for example to derive real-world drag values from the theoretic CD.

A bit of an anecdote, but take a look at your paper again. Check out the 90's BMWs with their below 0.30 CD. Now consider what the A = 1.000m^2 CD would be if the 0.30 CD was from an A of 1.700 - 1.800~.

This would also mean that AC's physics engine is incorrect, as correct drag values are attained by using CD x (Real surface area), with the CDA ending up correct, around 0.50's and so for your typical passenger car.

 

[Avo77]

Cd, Cl, Ceverything are just dimensionless coefficients that may be valid for vehicles with different surface areas.

High speed trains have the same Cd (or Cx) of a Porsche 911 but very different aero drag at the same speed.

P.S.
‘A’ is in the formula because it’s depending on the vehicle and not equal to one. Otherwise it would have been removed by using dimensional parameters like CxS (that is exactly the same as Cd*A).

 

[Kyuubeey]

Oh, I see now. I thought you were trying to say the CD and CL in the book/graph is CDA/CLA. You said everything is "normalized to the surface area" which I misunderstood as meaning "CD and CL are referenced with frontal surface area". CD and CL are "dimensionless", or referenced from A = 1.000m^2 as is basically anywhere ever. Apply the actual A to that -> CDA/CLA.

I was calculating force @ A = 1.000m^2 to get a baseline, you were using likely the 1.79m^2 provided to get the "real-world" value. Hence why you get a bit higher values. That, and the likely higher atm.

 

[monkef]

hello, thank you very much for these superb mods, just the gearbox ratios for the viper and chevrolet are too long, having a setting like on the ferrari 288gto choose between US gearbox. or europe would be absolutely great ! cordialy

 

[f1mate_Fisichella]

Unfortunately only the Corvette works for me, the other 2 crash the game...

 

[A3DR]

Unfortunately only the Corvette works for me, the other 2 crash the game...

From over 20k downloads nobody had that problem, so I wouldn't blame the cars. What's your setup for AC (vanilla, CM, CSP, etc)?

 

[f1mate_Fisichella]

From over 20k downloads nobody had that problem, so I wouldn't blame the cars. What's your setup for AC (vanilla, CM, CSP, etc)?

Completely vanilla, Steam version of the game. And it's not like the usual dropping back to the menu, but the game freezes while loading.