Quote:
Originally Posted by JulianEdgar
A few observations.
- The rear diffuser will work only if the floor ahead of it is also smooth. ie the airflow pattern ahead of the diffuser is critical.
- Measuring surface pressures will tell you at least as much as tufting.
- Trying to ascertain Cd accurately by road testing is, I think, impossible. Just go on changes to the total power (A * V), averaged over a long distance in two directions. Also, ensure that when you make a deliberate change to drag (eg by having the windows down), that change is clearly measurable. Otherwise, you may be measuring just noise.
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yes actually the rear diffuser goes along with a plate in front of the low hanging transverse bar. the undertray is flat from front bumper to battery end (approx 2/3 of the vehicle length), so this latter plate fills the gap betwen the battery end to the transverse bar, and then the diffuser from that bar to rear bumper.
For the Cd yes I just want to have relative variations of the CdA, not the absolute value one. the thing is on short test tracks if I don't have perfectly the same speed (cruise control is not always spot on) it can very rapidly pollute results. thus this approach allows to get partly rid of this variations (altough I would prefer use relative wind speed instead of gps speed..)