[Torcs-devel] aero stuff

[Christos D. <dim...@id...>]

I was just going through the aero code again. It is hard to find
figures for real cars, but I chanced across something in ferrari's
site which said that the ferrari 360 modena generates 200Kg at
300Km/h. In proper units, that is 2000N. Now, checking aero.cpp,
we have

total_lift = C * v^2 * hm, where C = 0.7+0.8 for the ferrari.
hm=2*exp(-3.0*(1.5*0.4)^4), [the 0.4 figure comes from the ride
height set up, though it could be even lower) really.

At a speed of 300Km/h this gives 8000 N, four times as much as the
original figure.

In order to bring it in line with the real figure, we need to either
change the C coefficients, or make it so that the car's front area and
Cx is taken into account.

We could change the line:
  hm = 2 * exp(-3.0*hm);
into:
  hm = FrntArea * Cx * exp(-3.0*hm);

I guess the 3.0 is arbitrary and could have been any other value.
Values near zero would indicate that the downforce is mostly due to
ground effect's decrease of pressure in the bottom and lower values
that it is mostly due the body's increase of pressure in the top.

I am sure that if we change this cars will be much more difficult to
handle. I don't know if the 360's value is representative of that of
other cars' downforce without any spoilers, but people on various
websites seem to value its downforce very highly. But perhaps they are
just echoing Ferrari's press release.


-- 
Christos Dimitrakakis
IDIAP (http://www.idiap.ch/~dimitrak/main.html)