I think I understand the trunk underspoiler a bit better now. On this web page, Honda states that the trunk underspoiler was added to the 2002 NSX to increase the speed of the air flowing between the trunk lid and the spoiler, reducing turbulence (and therefore aerodynamic drag).
Looking at my car closely, I saw that the gap between the wing and the trunk lid gets wider towards the rear of the car. It's shaped kind of like a reverse funnel. As the air flows under the wing into a widening space, it slows down. Because the air slows down, it cannot meet up with the air that flowed over the wing smoothly. Turbulence is created and drag is induced.
I bought a trunk underspoiler to have a look at it. It's not a typical spoiler that just kicks air up at the trailing edge of the trunk. Rather, it reshapes the space between the trunk lid and the wing so that it's a smooth channel with a constant height (see pictures below). The air does not lose velocity as it flows under the wing, it can meet up with the air that flowed over the wing smoothly, and turbulence is reduced. That could explain Honda's statement.
The NSX-R wing is mounted a lot higher than the standard wing. Maybe the gap between the trunk lid and the wing is so large that there's hardly any reverse venturi effect anyhow. If that effect isn't present, then adding an underspoiler won't decrease drag. It should still add a bit of downforce though, so maybe it was put on the NSX-R GT in order to get every last bit of downforce available. But that's just speculation.
Looking at the trunk lid, I think the underspoiler should decrease drag on any NSX with a standard rear wing and increase downforce a little as well.
PS: I coated my trunk lid with dirt in the pictures below so that you can see the contours better.:smile:
Looking at my car closely, I saw that the gap between the wing and the trunk lid gets wider towards the rear of the car. It's shaped kind of like a reverse funnel. As the air flows under the wing into a widening space, it slows down. Because the air slows down, it cannot meet up with the air that flowed over the wing smoothly. Turbulence is created and drag is induced.
I bought a trunk underspoiler to have a look at it. It's not a typical spoiler that just kicks air up at the trailing edge of the trunk. Rather, it reshapes the space between the trunk lid and the wing so that it's a smooth channel with a constant height (see pictures below). The air does not lose velocity as it flows under the wing, it can meet up with the air that flowed over the wing smoothly, and turbulence is reduced. That could explain Honda's statement.
The NSX-R wing is mounted a lot higher than the standard wing. Maybe the gap between the trunk lid and the wing is so large that there's hardly any reverse venturi effect anyhow. If that effect isn't present, then adding an underspoiler won't decrease drag. It should still add a bit of downforce though, so maybe it was put on the NSX-R GT in order to get every last bit of downforce available. But that's just speculation.
Looking at the trunk lid, I think the underspoiler should decrease drag on any NSX with a standard rear wing and increase downforce a little as well.
PS: I coated my trunk lid with dirt in the pictures below so that you can see the contours better.:smile:
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