nascar trucks?

[Christ]

I think (don't know, but think) the amount of energy used to send that extra little bit of air out and around the airdam (which is designed for downforce) is probably a losing situation when you could have just let it go under the vehicle.

I've been told (never verified it, don't follow NASCAR personally) that the NASCAR body cladding and wheel designs are used to create low-pressure under the car specifically to use pressure differentials (over versus under) to keep the vehicle on the ground. (Another downforce consideration). I'm not entirely sold on this, because it sounds too much like a mis-application of Bernoulli, the same one that schools still teach as being what makes airplanes fly.

[TEiN]

Originally Posted by Christ

I think (don't know, but think) the amount of energy used to send that extra little bit of air out and around the airdam (which is designed for downforce) is probably a losing situation when you could have just let it go under the vehicle.

I've been told (never verified it, don't follow NASCAR personally) that the NASCAR body cladding and wheel designs are used to create low-pressure under the car specifically to use pressure differentials (over versus under) to keep the vehicle on the ground. (Another downforce consideration). I'm not entirely sold on this, because it sounds too much like a mis-application of Bernoulli, the same one that schools still teach as being what makes airplanes fly.

To my understanding, that's pretty much the way it works. That very low air dam in front along with the "splitter" that juts out forward (and is buttressed by those shiny metal pieces you see hanging down) prevent most of the air from going under the car. Very little goes under, and a lot goes over. The thinking is that under the car is relatively low pressure while above the car is relatively high pressure (thereby creating downforce). Notice the black skirts down the side to keep side flowing air from intruding under the car.

Also, the splitter is like a chin that protrudes from the air dam and is parallel with the ground plane. A large quantity of air hits the vertical part of the air dam, and just about comes to a stop when the splitter prevents it from going under. That stopped air creates a large amount of down force (low velocity= high pressure). Creates a lot of drag too. The amount of downforce the splitter creates is can be adjusted by using a larger or smaller splitter. A small increase in the amount of splitter area on which that stalled air can act can create a large increase in downforce.

[MechEngVT]

Christ, I get where you're coming from as on the surface it does sound like high speed air over the roof should be low pressure (and it is) while lazy air under the truck should be high pressure, creating lift.

TEiN hit on one of the points and that is stagnation pressure at the vertical air dam above the chin splitter. The stagnation pressure pushes downward on the splitter creating heavy downforce. The high pressure (but not quite stagnation) at the base of the windshield does a similar thing on the hood. The spoiler on the decklid creates a similar downforce on the tonneau. The combination of splitter, windshield, and spoiler downforce is designed to overcome what lift results in the center of the roof.

Additionally by having slab sides run near the ground and an extremely low air dam/splitter there is very little to zero air flow going under the car. Because nearly all the air is pushed over and around the vehicle the air from the undercarriage gets vacuumed out the wheel openings and the rear end to the low-pressure areas along the sides and tailgate of the truck.

[Christ]

Originally Posted by MechEngVT

Christ, I get where you're coming from as on the surface it does sound like high speed air over the roof should be low pressure (and it is) while lazy air under the truck should be high pressure, creating lift.

TEiN hit on one of the points and that is stagnation pressure at the vertical air dam above the chin splitter. The stagnation pressure pushes downward on the splitter creating heavy downforce. The high pressure (but not quite stagnation) at the base of the windshield does a similar thing on the hood. The spoiler on the decklid creates a similar downforce on the tonneau. The combination of splitter, windshield, and spoiler downforce is designed to overcome what lift results in the center of the roof.

Additionally by having slab sides run near the ground and an extremely low air dam/splitter there is very little to zero air flow going under the car. Because nearly all the air is pushed over and around the vehicle the air from the undercarriage gets vacuumed out the wheel openings and the rear end to the low-pressure areas along the sides and tailgate of the truck.

That's what they told me about the wheels being shaped/designed like they are, to pull air out from under the vehicle, what little bit of it can still get under there.