nascar trucks?
 

i can across this picture on the internet and i figure that the nascar truck teams must do more aerodynamic testing than anyone. i think that they do not use a aerocap design because i would imagine that the truck sponsors want the trucks to resemble a production truck. so i am wondering if the same results as a aero cap can be achieved with a torrnea cover and a rear spoiler? does the air going over the truck pass over top of cab and then the rear spoiler act as if there is a aero cap on the truck?

also i am wondering why they went with a air dam instead of a belly pan? i can see that the truck is lowered and the air dam is really close to the road with side skirts

i know their concern is not fuel economy but the aerodynamics must apply to fuel economy





[IMG]http://i964.photobucket.com/albums/a...ascartruck.jpg[/IMG]

Well, they do and don't.

They're more interested in downforce than anything else, which is nice for when you're going 200 MPH around a corner, ya know?

I'll try to find it again, there was a webpost somewhere (that I probably didn't save) which detailed the Cd and A of the newest NASCAR vehicles, including the trucks. IIRC, they were about average for our purposes, but can make 1,000's of lbs of downforce at speed.

Yeah, Downforce...I say it's over rated. But 4 out of 5 NASCAR crew chiefs recommend it for their drivers.

http://ecomodder.com/forum/attachmen...1&d=1265992841

Hey, that's cheating! No fair passing by flying over the car ahead.

...Motorsport News headline: "Leap Frogging driving technique not quite perfected at Daytona."

That air dam is too low for the street but I'd imagine it's so low that a belly pan would be largely redundant i.e. a pan would do little good.

I'm sure, knowing Nascar that there are restrictions as to what can be done to the underbody as well.

Both the design of the air dam and the rear spoiler are specified by NASCAR

Disappointingly, a Google Image Search for "salt flats pickup truck" doesn't yield anything more than airdams and tonneau covers.

http://minitruckzone.tenmagazines.co...ages/33878.jpg

^ Desperately needs rear wheel skirts and a teardrop-shaped bed.

wondering
 

cc, the teams spend an enormous amount in wind tunnel time to evaluate drag vs downforce.
NASCAR probably forbids aeroshells as they would not match 'Templates' used by officials to 'pass' vehicles.
A carefully designed cab-wing/sail panel,along with a 1/2-tonneau can approach the drag reduction of an aeroshell.
The locked-vortex behind the cab,and above the tonneau on the NASCAR truck creates a 'phantom' shell with outer flow skipping over.
The rear spoiler is only for downforce.
The airdam and skirts form a duct which allows the low base pressure of the wake to communicate underneath for downforce.More drag.
Hucho uses the term 'minimum' for airdams.Too much of a good thing and your drag begins to go back up.And the drag increase can be remarkable!

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.

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.