- How you calculate CPL variations ? (I do not ask PI as Dave already said somewhere the is a secret!)
CPL variation is traditionally an ASD (auto-spectral density) of tire vertical load viewed in the frequency domain, though there are numerous methods that are used in both motorsports and production cars involving manipulations of that data before and after transforming it into the spectral (frequency) domain. Windowing, shaping, filtering are all often used to some degree dependent upon the specimen and test of interest. In the time domain, calculating an Root Mean Square (RMS) Load is also common. There is a significant amount of analysis performed in both the time and frequency domain in addition to the above, but you will start to venture into the proprietary realm...especially if you are interested in calculations of "grip" and it's effects on handling.
Personally, I prefer to analyze in the spectral domain. If you are interested, study up on Fourier/LaPlace Transforms and the properties of Fast Fourier Transforms (FFTs), which you will use with measured (discrete) data. It is easy to get useless/invalid results if you don't keep track of what you're transforming.
- I got some test done on F3 cars, and I see some pitch coupling, pitch damping and heave damping, what do really mean? is it possible to know how you calculate them to get a more deeper understanding?
Great thread, keep it alive!
You will have to be more specific about what you are referring to. I would assume that your pitch coupling
is the magnitude of a Transfer Function with a Pitch Accel output and a Heave accel input (likely from a "in-phase" sinesweep excitation), though there are other ways to determine it. Pitch and Heave damping
could mean many things depending upon what is instrumented on your vehicle:
1.)Assuming you simply installed your racecar on a rig and attached accelerometers to the hubs and body, heave [pitch] damping could be a measured F-V curve using calculated relative displacements [pitch angles] and CPL load [CPL pitch load].
2.) It could relate to energy dissipated by tires/dampers compared to input energy, where phase angles between actuators and the tires and body become important.
3.) Maybe your F3 had instrumented dampers and shock potentiometers and it is simply a measured F-V curve at the damper.
4.) Perhaps your vehicle was used to generate parameters for a simplified simulation, which is analyzed modally.
The point is that most rigs seem to do things a bit differently; they may even use the same naming and signal convention. You need to direct these questions to the engineers administering the tests, anybody else would be simply guessing (just like me). I'm not aware of any standardization regarding these kind of analyses, so someone please correct me if I'm wrong.