Quote:
Originally Posted by JulianEdgar
Huh?
We want the downforce to be completely offset by the lift. Or the lift to be completely offset by the downforce. That is, no net lift or downforce. Of the whole vehicle. It's one entity!
It seems pretty simple to me!
Net = key point.
It's one reason that cars with very low drag (eg Tesla Model S) have such low coefficients of front and rear lift.
Expansion:
Consider an object in space. We can apply a force in one direction, let's call that 'lift'. We can apply a force in the opposite direction - let's call that 'downforce'.
If we have 'lift' forces occurring, and we don't want the body to accelerate, we need to apply 'downforce'. When lift and downforce are equal, we have no body acceleration. We don't then regard 'downforce' as significant; it's just been balanced by 'lift'. The body is then in equilibrium.
And in regard to cars, in this case the net pressures on the top surfaces are the equal and opposite the net pressures on the bottom.
I think - and this is an educated guess - with no lift/downforce net differential, the strength of trailing vortices is much reduced, so explaining the reduction (to nil in this case) of induced drag.
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They would be a function of a pressure/velocity discrepancy between any two adjoining flow fields (like body sides and roof) and how the differentials induced span-wise flow under a physical imperative to attain equilibrium.
On Ahmed body investigations,all vorticity could be eliminated by tuning the rear roof slope,boat-tailing,and diffuser angle.Same way Cybertruck may come in at around Cd 0.28.Without mirrors of course.