Temperature effects on Aerodynamics?

Discussion in 'General Discussion' started by PLAYLIFE, Mar 26, 2012.

1. PLAYLIFEMember

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Does the temperature effect the aerodynamics? From a pretty quick test and some back-of-the-envelope calculations, I'm lead to believe that ambient temperature doesn't effect aerodynamics.

The test
Run the WSR3.5 car on a section of straight and note the average force on each tyre using MoTeC. Same aero configuration.

Conditions
a)
0°C, 0% humidity
Resultant air density is 1.29 kg/m3

b)
60°C, 0% humidity
Resultant air density is 1.06 kg/m3

Air density changes and is proportional to atmospheric pressure and temperature. Since the pressure and gas constant are identical in each case the only variable is temperature and the swing of 60°C is substantial. So obviously a large change in density will result from a large change in temperature.

Downforce/lift is ruled by air density, velocity (squared), coefficient of lift of the object and the object's frontal area. Obviously keeping everything the same except density, and given density is significantly different, we should see those differences in the downforce level (force on tyres) in MoTeC.

Results
a) 0°C, 0% humidity
Average force (N) of tyres over section:
Fronts = 4322 N
Rears = 5742 N
Average velocity* = 75.8 m/s
We will denote this condition as our baseline downforce, thus = 1.0

b) 60°C, 0% humidity
Average force (N) of tyres over section:
Fronts = 4347 N
Rears = 5759 N
Average velocity* = 75.5 m/s
Under these conditions, we expect a downforce value to be approximately = 82% of baseline yet we saw effectively the same forces as the 0°C condition.

Conclusion
No difference. Temperature does not effect the aerodynamics.

Discussion
I haven't yet tested the effect of humidity as I figure if temperature has no effect, humidity won't either. You may think 'big deal' and sure I can understand that, but the effect of temperature can be as much as 20% loss of downforce in the case above. Added to that, humidity will increase these differences too.

Not sure if ISI are planning to have the environment effect the aerodynamics in the future, but given the nature and influence of ambient conditions on aero, it would be a nice to have and I would have thought be fundamental in a solid aerodynamic model.

Limitations
Please let me know if I've missed anything in this quick test. The only potential caveat I can see is MoTeC's readings.
*despite the square of velocity, the difference is negligible. In fact, it may be the reason for the minute difference between the forces.

Edit, forgot to add velocity in the test cases

Last edited by a moderator: Mar 26, 2012
2. mclaren777Registered

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Excellent detective work!

3. taufikpRegistered

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And hopefully the side wind effect will be implemented too.

4. CdnRacerBanned

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Interesting find. You are right that humidity wouldn't of done anything since it isn't plugged in yet and either is wind.

5. PLAYLIFEMember

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Yeh I thought I had read somewhere that humidity wasn't yet implemented so lucky I did hold off, although I will eventually do the test in the future anyway.

6. ROONRegistered

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Interesting stuff. I was wondering about this very same subject after listening to the Sky F1 team discussing the lack of downforce in Sepang due to the extreme temperatures and humidity. Would be great if we could get that level of realism implemented into rF2.

7. Guy MoultonRegistered

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How do you test this? Are you going the EXACT same speed on every run? At 0C you will get poor lap times and slower laps because of the temperature of the track and tires. At 60C you will experience engine problems but good traction. The differences in lap times and conditions may account for the differences in df since lap times should be VERY different.

8. taufikpRegistered

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Afaik, you can change environment variables in Race Settings menu. But the actual physics code is still not implemented yet.

9. Marek LesniakCar TeamStaff Member

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No need to go through corners to measure downforce values. Just use long enough straight to keep steady speed for a few sec (so that forces acting on the car stabilize) and that's it.

10. TJonesRegistered

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Not only that Aerodynamic downforce isn´t affected by temperature, tyre temp and grip are also not affected by enviroment temp.
Also track conditions, wet or dry has no, or much to less influence on tyre surface temperature.
However track conditions (wet, dry, tyre abrasion), are already affecting grip.

Still a long way to go.

11. PLAYLIFEMember

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I set 6th gear so the car maxes out at 275km/hr. Took it to Spa and took an average speed over a set distance.
I stated in each run what that average speed over the section of road was: 75.8 m/s and 75.5 m/s respectively.

You can't do it at a single point, you need to do an average over a set distance to account for any reading spikes or anomalies.

- It has nothing to do with lap-times, it was a straight line test.
- The track has effectively no effect on top speed, hence why I could replicate an almost identical average speed over the set distance.
- 'Engine problems' doesn't change the amount of downforce the car is generating.
- Lap time was not measured, only downforce generated by the car.
- The downforce was effectively identical in both cases.

12. PLAYLIFEMember

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That would explain it

Is it expected that the environment plugs into the physics? I'm not sure if I've read anywhere that that is the intention of the dynamic environment (apart from tyre grip). If not, it would be a shame.

In order to calculate generated downforce, you need to use air density. I'm hoping the objective is to pluck the real-time air density from the current conditions rather than using the air density at standard conditions (sea level at 15°C, 1.225 kg/m^3).

13. PLAYLIFEMember

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*bump*

Haven't tried it with the new build, anyone tried?

Also, not only should temperature effects aerodynamics, but also seriously effect engine power too.

Added to both of these, aero and engine, (have documented the latter in another thread), the effect of altitude/elevation should see similar results.

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14. LazzaRegistered

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Knownissues says wind and humidity do nothing. The fact this is acknowledged but they are there strongly suggests both will have an effect in future, implementing those would do 95% of the work required to add in a "current pressure" parameter to also affect the aerodynamics. The engine would be slightly different, and not sure if the parameters are in the engine file for that just yet.

Wonder which will come first - wind/humidity, or the missing link(s) for tyre behaviour on a wet track?

15. NiboMember

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I tested. Temperature does not affect lap times at all. At 0 degrees and at 35 degrees lap times are identical (at Sepang).

16. PLAYLIFEMember

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Although the end result is lap-time differences, the only real way to test it is to do a test as I've shown in post #1. Observing force values on the tyres at a given speed (by using an average speed over a set distance) is the only way to isolate the effect of ambient conditions on the aerodynamic model. This is where MoTeC becomes our best friend.

Using this method eliminates any influences of track condition (rubber), driver influences (mistakes) etc.

17. AlesiRegistered

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also would be cool if car's peak power may vary a bit from track to track, because of ambient air pressure as part of the engine torque calculations, so things like elevation and weather will have an influence on engine power

18. 03yatmicRegistered

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Where is the downforce level in MoTec?
Are you using MoTec i2 Pro?

19. Timpie ClaessensRegistered

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So we're more then a year on, released status (natural progression from beta) and the same things still aren't working?

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