Re: Some simuv2 aerodynamics questions

Firstly, I have a book on aerodynamics, but it has not been much help.

> 
> 1) I've got some mix-and-match in the units side. The code seems to be 
> working mostly with SI units. However, the xml files have milimetres, 
> imperial (springs) and some others. Is there any list of what isn't SI in 
> the code? I'm basically doubting ride_height.
> 
I think the code understands many units.  No idea where the translation 
is though.  Why not try substituting mm with m, or inches, and see what 
happens?  I think it works OK.

> 2) Drag due to yaw =/=0 seems not implemented. See line 87. How much this 
> affects drifting? Would it be worth to run a couple of tests adding the 
> lateral area of the car into account or would I be wasting my time?
> 
I have this in simuv3.

> 3) On line 87, the drag reduction due to slipstreaming (dragK) is squared. 
> Is there any easy explanation for that?
> 
You are misreading the code.  dragK has two things integrated: the drag 
coefficient and the speed, so this is why it is squared.

> 4) Christos explains in his site that ground effect goes like
>        F_i= C_i*v²*exp(-b*h)
> It struck me to see ride height fully averaged instead of "axis averaged". 
> Is this intended for ease-of-setup? (balance is thus fully determined by 
> front and rear Clift).

Basically yeah, in fact it'd be difficult to determine what happens 
exactly when the front part is lower than the rear part, as the systems 
are connected.  Averaging everything is easier and good enough.

> 5) The actual ground effect formula seems to have the average height at the 
> fourth power. This differs from what is stated here, 
> http://www.idiap.ch/~dimitrak/torcs/carsetup.html but, again, simuv2 is 
> supposed to provide four times too much downforce. Is this the cause?
> 
no, the formula exp(-bh^4) just tells you how much the downforce 
_reduces_ when the car is further away from the ground. (my page has 
left out the ^4 factor).  The cause is simply in the selection of 
downforce constants.  For example, if you look at the claims made by 
ferrari about their 360-modena car, they indicate a total aerodynamic 
downforce factor that is around 4 times less than the one in torcs for 
this car.  Look also at the next question.


> 6) Wing efficiency L/D = wing->Kz / wing->Kx is 4.0. Is this high? Low? 
> I've been googling a short time, and the closest I've seen is a L/D list of 
> airplane wings and birds in wikipedia, and 4 is on the low side.
> 

L/D also depends on the angle of attack, wing size and geometry. 
However a simple upper bound on L/D is given by energy conservation and 
it depends just on wing size and angle of attack, and I am using it 
experimentally

> Finally, I'm sure all of you have noticed how even small amount of damage 
> has a large impact in laptimes in fast ovals and e-track 4, while one can 
> lap within 1 second or so in e-track 1 and g-track 2 and the other slow 
> tracks with damage upwards of 2000. Would it be very silly to implement a 
> bodywork downforce penalty similar to the drag penalty? The most obvious 
> effect I see is that robots might be penalised by not accounting for 
> downforce correctly.
> 

Well, I played for a bit with a 'randomizer' that made the wing forces 
deviating from just centrally applied backwards and downwards forces. 
This was really interesting in some cases as it really messed up your 
driving.

> Thanks a lot for your answers and your patiente if you made it this far. 
> Regards,
> 
> Miguel
> 
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