31 replies to this topic

[OfficeLinebacker]

Hey guys, I was reading this article on NASCAR.com:

http://www.nascar.co...ory_single.html

and couldn't help but notice that the car has four NACA ducts all crammed into the space of the rear window.

Now, we all know T-Stew is a big, sweaty guy who needs his cooling, and that's OK. But at this point, wouldn't it be more efficient to just figure out the largest single NACA duct that would fit into that plane and just go with that?

Those four NACA ducts clustered in like that just looks comical to me.

What say you, brethren?

[Greg Locock]

They may look like NACA ducts, but I'm pretty confident they aren't.

[NRoshier]

They look like the aftermarket NACA style duct to round ducting intakes. They are usually quite a poor shape as far as a true naca duct is meant to be.
Could they be used for diff cooler etc?

[cheapracer]

Maybe different pressure points along the window there? Are they intakes or extractors?

[Bill Sherwood]

Originally posted by cheapracer
Maybe different pressure points along the window there? Are they intakes or extractors?

I can't understand the use of NACA ducts in reverse. They (don't!) suck!

[Greg Locock]

NACA Duct:

Laminar flow

Thin boundary layer

Pointing into airstream

Slightly strange looking shape.


1 out of 4 ain't bad.

[NRoshier]

NACA duct - inlet angle varies with O/A length/width, sharp sides to duct the create vortex, shaped LE to rear-most part of duct. As Greg says, good for laminar flow at higher Re.

[cheapracer]

Originally posted by Bill Sherwood


I can't understand the use of NACA ducts in reverse. They (don't!) suck!

I don't know a heap about aero's, it just looked like the pipes were facing forward thats why i asked - upon looking at other shots there also seems to more to the ducts, notice the what looks like rubber diaphram valves at the head of the pipes ..

http://sports.yahoo....nhms107&prov=ap

Here's his face duct

http://sports.yahoo....300_&prov=getty

[jatwarks]

I would suggest that the 4 ducts are simply cut to the size of the 4 pipes. Having the 4, round inlet pipes fed from a single large duct would be more complex, and less efficient, as the shape of the duct would have to split into 4 anyway, as the pipes clearly lead off to different destinations.

1 into 1 four times is more efficient than 1 flat duct into 4 round pipes.

The Engineers got it right, in my opinion.

Jim

[OfficeLinebacker]

Originally posted by jatwarks
I would suggest that the 4 ducts are simply cut to the size of the 4 pipes. Having the 4, round inlet pipes fed from a single large duct would be more complex, and less efficient, as the shape of the duct would have to split into 4 anyway, as the pipes clearly lead off to different destinations.

1 into 1 four times is more efficient than 1 flat duct into 4 round pipes.

The Engineers got it right, in my opinion.

Jim

That was pretty much my guess as well.

[zac510]

I see one huge duct: the door window

[Greg Locock]

Incidentally here's the original report


http://naca.central....rt.php?NID=2176



And here's what they should be using in roughly those locations for intakes .


http://ntrs.nasa.gov..._1993092958.pdf

[jatwarks]

Originally posted by jatwarks 1 into 1 four times is more efficient than 1 flat duct into 4 round pipes.

I felt I should qualify my statement.

If we were talking about F1 instead of NASCAR then my statement would probably be less true. It is true in this case because nobody in NASCAR needs to spend excessive R & D time and money perfecting the solution when several meters of flexible tube are adequate.

'Fit for Purpose' is the key phrase.

Jim.

[Fat Boy]

I get the feeling around here that it's not understood just how much aero work the 'good old boys' down south (up north for you, Greg) do. Don't let the accents fool you. They are very smart and very savvy when it comes to racing a stock car.

I'm sure they can't run a scoop because of rules issues about protruding from the window.

My guess is that they've made the NACA specific ducts and found very little gain between them and the $10 cheapies that you can get from the BSR truck. So it turns into a cost/benefit type thing.

[Greg Locock]

My point was, not that they wouldn't work, not that they hadn't been optimised, but that they were not, strictly, NACA ducts, which by definition are forward facing intakes of a particular shape that operate in thin boundary layers compared with their depth.

I agree they couldn't really use ram type scoops.

[Fat Boy]

Originally posted by Greg Locock
that they were not, strictly, NACA ducts

Very true. The guy on the parts truck would call them NACA's and so would pretty much everyone in the paddock. You are correct, though. Incidiently, did you see the 2 papers in the sticky? They're interesting in a historic kind of way.

[NRoshier]

I have no illusions as to the level of skill and development in NASCAR. I'm not sure I like it, but then I am not it's market.

[McGuire]

Originally posted by Fat Boy


Very true. The guy on the parts truck would call them NACA's and so would pretty much everyone in the paddock. You are correct, though. Incidiently, did you see the 2 papers in the sticky? They're interesting in a historic kind of way.

Yes, the papers are very interesting. They are also over 60 years old and they are about aircraft. Gee, maybe the NASCAR application is not about absolute minimum drag but maximum flow and calls for some variation, say with a larger throat in the floor of the duct.

The Gibbs #20 car pictured at the top of the thread is in short-track configuration, with multiple ducts to the rear brakes and diff cooler. In regard to the minor downward angle, that is a pretty good picture of the local airflow around the sail panel, as determined in ten zillion hours of wind tunnel testing. Three or four ducts per quarter window is the norm for a short-track car. There are typically 12V blowers in the ducts as well. On an intermediate or speedway car you may see one duct per side or none. On some intermediate/big track cars you may see one inlet that is very close to an original NACA duct, on the Roush cars for example. For qualifying they will shut off the blowers and seal the inlets with clear cargo tape.

EDIT: Interesting that the subject of ductwork should come up as NASCAR is currently taking a very hard look to make sure nobody is using it to pick up a few counts of downforce.

[Fat Boy]

Originally posted by McGuire


Yes, the papers are very interesting. They are also over 60 years old and they are about aircraft. Gee, maybe the NASCAR application is not about absolute minimum drag but maximum flow and calls for some variation, say with a larger throat in the floor of the duct.

If your point is to disagree with me, you're not doing a great job of it. Your post comes across as pissy, and for the life of me, I don't know why.

[McGuire]

Originally posted by Fat Boy


If your point is to disagree with me, you're not doing a great job of it. Your post comes across as pissy, and for the life of me, I don't know why.

Nope, wasn't disagreeing with you at all.

[Bill Sherwood]

I was thinking about this today - I wonder if they're taking some of the air out of the back of the top of the car, and perhaps dumping it under the rear ..... to try to reduce drag .. ?

[phantom II]

Hey, how come you not on FB’s **** list? He likes you best . I’m devastated.

Originally posted by McGuire


Nope, wasn't disagreeing with you at all.

[NRoshier]

Originally posted by Bill Sherwood
I was thinking about this today - I wonder if they're taking some of the air out of the back of the top of the car, and perhaps dumping it under the rear ..... to try to reduce drag .. ?

and increase lift?

[McGuire]

Originally posted by Bill Sherwood
I was thinking about this today - I wonder if they're taking some of the air out of the back of the top of the car, and perhaps dumping it under the rear ..... to try to reduce drag .. ?

Don't know about that, but with the CoT drivers are reporting that they can feel the front grip change when they turn the front brake blowers on/off.

[OfficeLinebacker]

Originally posted by McGuire


Don't know about that, but with the CoT drivers are reporting that they can feel the front grip change when they turn the front brake blowers on/off.

LOL I have suspected this for months now, even on the old cars.

I have known about the brake fans, diff fans, and of course rad fan for years now.

Then I read about the infamous fan cars.

Then a little light went on and I thought, "Some NASCAR team has to hire me!"

Then another light went on and I realized that the better teams (eg Chad Knaus) had figured it out already.

Then I started listening to the in-car radios and whaddya know, the crew chiefs are directly telling their drivers how to use the fans to manipulate downforce.

yeah, they're using ductwork to pick up downforce. Earth to Robin Pemberton!

[McGuire]

Originally posted by OfficeLinebacker


yeah, they're using ductwork to pick up downforce. Earth to Robin Pemberton!

So far it's just a few counts of downforce this way and that.

[Ross Stonefeld]

Enough to tune for balance?

[imaginesix]

Originally posted by McGuire
Don't know about that, but with the CoT drivers are reporting that they can feel the front grip change when they turn the front brake blowers on/off.

I'll have to test drive a Malibu and try that for myself. Sounds fun.

[McGuire]

[OfficeLinebacker]

Originally posted by Greg Locock
They may look like NACA ducts, but I'm pretty confident they aren't.

Just wanted to update that I am listening to the Tony Stewart's frequency for the Kansas NASCAR race. He slid across the grass and after pitted quickly for tires and cursory scrubbing of the screen. As he came around his crew chief called him in for a second, more thorough going-over. He said "We have time, we might as well check the NACA ducts and everything like that."

So even the man in charge of the car calls them NACA ducts.

[Greg Locock]

One more time.

We know that people call them NACA ducts.

"When I use a word," Humpty Dumpty said, in rather a scornful tone, "it means just what I choose it to mean--nether more nor less."

"The question is," said Alice, "whether you can make words mean so many different things."

"The question is," said Humpty Dumpty, "which is to be the master--that's all."

[OfficeLinebacker]

Originally posted by Greg Locock
One more time.

We know that people call them NACA ducts.

"When I use a word," Humpty Dumpty said, in rather a scornful tone, "it means just what I choose it to mean--nether more nor less."

"The question is," said Alice, "whether you can make words mean so many different things."

"The question is," said Humpty Dumpty, "which is to be the master--that's all."

Greg Locock,

You're crazy, man. You're crazy. I like you, but you're crazy.