Quote:
Originally Posted by 2000mc
“no vertical force (ie no lift/downforce) is best for lowest drag” is easy for me to agree with, but I would think that would apply to any given surface, rather than net lift/downforce of the entire vehicle
if the upper surface's lift are completely offset by the lower surface's downforce, then there will be less drag than if the situation were different.
To me, inducing additional downforce goes against “no vertical force (ie no lift/downforce) is best for lowest drag”
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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.