naca ducts

[deaf_rattle]

Does anyone know where do buy naca ducts from?

CHeers

[nobody]

You could ask the seller of this to relist:

http://www.trademe.co.nz/Browse/Listing.aspx?id=266709016

Or contact them through their website: http://www.riverscarbon.com/

[KinLoud]

It always puzzles me when I look at the naca ducts you can buy for motor sport...
It's obvious that whoever makes them didn't read the technical info about how they work and what parts of the design is critical.

A very important part of the design to produce a low drag and efficient duct is to have sharp corners between the flush surface and the duct itself.
Like these ones




The ones you find sold for motorsport have a rounded radius lip which is much less efficient. Is it too tricky for them to make or are they just lazy or do they think people don't know/don't care if the duct doesn't work properly?


My 2 cents worth anyway!

Ken

[Adamal]

Valid point Ken.

Wouldn't the one pictured actually act in the opposite way you want? Like to have air flowing over the top of it would work to suck air out.
When you have the angled floor of it, it then acts as a scoop, which does force air in there.

[sergei]

That carbon fibre one wouldn't even work due to pipe being there...

[Malcolm]

Apparently the Rivers one does work very effectively, the design is modelled off one that sees considerable use in race cars for cabin cooling vents (the kind people put into the rear side windows of their race cars). The question of drag is probably not so easily addressed, that sort of thing would require some sort of instrumented testing to establish drag values.

[Malcolm]

That carbon fibre one wouldn't even work due to pipe being there...

as usual, you have no idea what you're talking about.

[sergei]

That carbon fibre one wouldn't even work due to pipe being there...

as usual, you have no idea what you're talking about.

Thanks.
I admit sometimes I am being wrong, but not every $&#$% time to warrant "usual".

[sergei]

Instead of being an ass, you should have pointed why I am wrong.

Here is the reasoning why that carbon fibre duct will not even work:

The duct works because the opening is narrow at the tip and widens at the end.

Adding a sharp angled pipe flange creates narrowing, which will result in lower pressure region counteracting the higher pressure just before, hence hindering the flow.

EDIT: Reworded, removed brain fart garbage.

[Malcolm]

it's not always that simple. You have (relatively) high speed air flow before the entrance, the duct gradually increases in cross sectional area which slows the air down to create high pressue. This high pressure is then used to force the air toward where you want it to go.

Whilst reducing the area at pipe is going to cause some restriction, it's not going to be an obscene amount. Yes, a larger outlet could potentially give you more flow, but from a standpoint of practicality I don't think many people want 4" diameter hoses running through their cabins unless they REALLY need it. So maybe the NACA duct itself should be smaller, so there's no reduction in area? Well I have to admit to not having an in-depth knowledge of aerodynamics - but I would presume the larger NACA duct still provides a higher pressure and therefore a higher flow rate through a given size of tubing than a smaller one would.

When it comes to aerodynamics, things tend to be quite complicated. I would suggest that if you have no decent training/experience on the matter you should refrain from doing your eyeball CFD and making bold statements like "it wont work because of the pipe."

Maybe my statement about it being "usual" for you to not know what you're talking about was unfair, the basis for it is that I very frequently see you passing off an assumption or an opinion as if it is a fact, and that sort of shit on internet forums can be very misleading for younger/less knowledgable people who see such statements from old folk and assume it is somehow factual.

[Malcolm]

I should add as a bit of a caveat, I don't necessarily think/know/have anywhere near the requisite knowledge to judge whether the design of the NACA duct that Rivers are selling is necessarily well designed or particularly efficient, but if you have a look at Nascars you'll see a significant use of virtually identically shaped ducts.

[sergei]

I agree, I assumed certain things about duct above, I used my intuition to assume.

As me assuming too much, do you keep the count? Could you point the blatant lies on my behalf in technical section please?

This is a forum.
Forum is for discussion, this is not a technical library, if people don't have their own brains to apply and blindly follow other peoples opinions be that malicious or based on wrong assumptions, it is their own fault.

I have personally done many stupid things in my life following other peoples advises, but learned to double and triple check and do my own research.

[Malcolm]

As me assuming too much, do you keep the count? Could you point the blatant lies on my behalf in technical section please?

I don't have a burning desire to score points here, and haven't the inclination to spend time going through the forums to try and prove a point. I think you should just be more thoughtful about making it obvious when you're guessing at things.

[sergei]

As me assuming too much, do you keep the count? Could you point the blatant lies on my behalf in technical section please?

I don't have a burning desire to score points here, and haven't the inclination to spend time going through the forums to try and prove a point. I think you should just be more thoughtful about making it obvious when you're guessing at things.

point taken.

[RS13]

Lol.. NACA ducts don't use pressure as such, they use the curving profiles of the walls to draw the boundary layer vortices away from the intake flow, which draws the laminar flow in without slowing it down. The air enters the ducting and provides a positive pressure for say, a fuel tank in an aircraft wing.

Kinloud, I've seen a few now that have reasonably rounded edges, perhaps it relates to the design speed at which the duct operates? The outboard surge tank vent on a 737 compared to the light aircraft in your pictures?

[XSDRIFT]

As an idea, if people are interested in some fibreglass work/builds to be done I may be able to assist. Dabbling in the art at the moment and building myself a replacement headlight duct to ram air to my filter.

Not 100% on the science side of the ducts being talked about but able to investigate and do some trials with them if there is enough interest.

[matt dunn]

Did you find a supplier?

http://www.racerindustries.com/store/in ... cts_id=203

PM me if your still looking as I know a NZ supplier that will have them,
but will have to find their details, Dad deals with him quite a bit.