# Aerodynamics discussion

Discussion in 'Car Modding' started by jtbo, Jul 26, 2012.

1. ### Niels_at_homeRegistered

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Just browsing the tread, so I may be missing the point, but rFactor uses Force (Newton) = coefficient * speed (m/s)^2

So with a drag value of 0.45 and a speed of 200km/h (56m/s), the drag force = 0.45 * 56^2 = 1389N. That means there is no air densitiy in rFactor. If you want to simulate a hot / high altitude race, you'd have to lower the coefficients in the HDV file, and probably take some power out of the engine..

2. ### jtboRegistered

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New engine model had some constants for that from my (poor) memory, bit OT, but might be worth to explore:

3. ### lordpantsingtonRegistered

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Don't think that no one is answering because they don't know how, rather because it is hard to explain and difficult to accomplish. As told to me by our resident Aero guru: the moment generated by a wing is not the force acting on the tire. The load is acting on the entire body. Likewise a splitter or front wing is doing the same. The result is measured as their effect at the wheels.

Nonetheless I also have been searching for a mathematical model.

Last edited by a moderator: Oct 27, 2012
4. ### newtonpgRegistered

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Thanks lordpantsington for your time. Really appreciated

I would be gratefull if you (or someone) can advise any related literature.

PS: As an agronomist, I always will remember your location as the home of the (old) famous lettuce variety.

5. ### lordpantsingtonRegistered

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I never knew about the lettuce.

I've been googling for aerodocs, and there are definitely some interesting reads. But I've yet to find paydirt.

Last edited by a moderator: Oct 31, 2012
6. ### jtboRegistered

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HP Wizard seems to have Aerodynamics page, which I haven't noticed before there or then it is just new.

I did some testing with car I have data and it really gets quite close, surprisingly close, imo.

If one has limited data, that can help to get you into range, check it out and tell what do you think about it:
http://hpwizard.com/aerodynamics.html

7. ### osellaRegistered

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I believe no car sim ever simulates altitude effects, we talked about it several times on these boards, but probably never received any answer from ISI, it just seems its not important for devs.
Which is understandable since racing circuits tend to be all low altitude.

Although for a track like Hermanos RodrÃ­guez or Pikes Peak climb there are quite drastic consequences of high altitude.
I actually did for a few historx cars exactly what you suggest about 1 year ago: I made an upgrade called "pikes peak package" for those cars that decreased engine power by some 30-35% and lowered drag. Still not realistic of course, because the trick of that hillclimb is that finish is 1400m higher than start. Still much better than having 100% power all the time.

Cool site jtbo, I never really knew how and why Cd is so different from what I expected.

8. ### Marek LesniakCar TeamStaff Member

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iRacing probably does that... and I think rF 2 is on a good way to also simulate that too.

9. ### osellaRegistered

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Oh seems you're right, although I couldn't find to what depth it is simulated in iR.
If it should be simulated to all extent that would be pretty interesting because high altitude makes some cars slower while other cars faster.

10. ### lordpantsingtonRegistered

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I've something to add here, with great thanks to Jim Pejsa for cluing me in. In post #8 I did this calc:
This calculation only works correctly if your RWRange starts at 1, and steps by 1.
If for instance I was using
the calculation above would be:
-.0697+(-.013*19)+(.0003*19*19)=-0.2084
-.2065*44.704*44.704=-416.47648...N (-93.63#).

11. ### newtonpgRegistered

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Thanks lordpantsington, now CoL (and CoD, obviously) calculus makes sense to me!

12. ### 64rRegistered

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Using the plugin data, you can see a Tyre Load channel for each wheel of the car, this is the vertical load force through each tyre. Using this and the Ride Height channel you should be able to model the vertical loads quite accurately. The way racing teams do this in the real world to analyse and model wings etc is to drive down the straights at a constant speed (so that the test is repeatable anywhere) with different wing positions, eg, do a run at 80, 120, 150 and 200kph for each wing configuration. You will end up with a model that shows the different loads for each different wing configuration. If you have the maths skills and know something about the wing that you are modelling this should give you the data that you are after.

13. ### lordpantsingtonRegistered

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What does ride height have to do with it? Wouldn't you just take the change in load between moving and stationary?

14. ### newtonpgRegistered

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Regarding that, we can assume that "Tire Load" doesn't include any aero forces?