NACA submerged duct how to

[sinner720st]

a couple weeks ago i put a hood scoop on my hood that i made, afterwards i did the research and stumbled upon NACA duct...

it was developed in the 40's as a way to take air in through the body or fuselage of airplanes, without creating ant drag...

it works by creating two vortex's that break through the slow moving boundary layer of air and drawing in fast moving air from higher up.

 

 

NACA= national advisory committee for aeronautics

 

so i looked at other forums as a result from google search and found some shit other people came up with, some good, some not.

i finally found the actual research write-up that some smart aerodynamicist spent lots of time getting right.

 

here is the link to the original> http://naca.central....ca-rm-a7i30.pdf

 

you could spend all day reading it then another day figuring out his math, or skim through first few pages, then skip to drawings

 

 

a pretty good example of a well executed duct, this one is on an airplane being used as an oil cooler

some things of importance i found from the nacs write-up

the best width to depth ratio is anywhere from 3 to 5, this meaning if you want an opening (in my case)

9.25" wide you divide that by either 3,4,or 5. i used 5, this gave me a depth of 1.8".

once you know your opening you then can find how long your duct will be, the optimal angle of the bottom of the duct is 5*, or 7*, mine is a little proud of seven (a good link for angle stuff rise run angle calc. )

now you have a pretty good side and top view started.

to finish your top view you need to divide your length into ten parts (o% to 100%)

after you have divided your drawing (make sure everything is square/parralell)

you can take the table in fig.3 of the naca paper and plot the point of your top view planform

% x(w)

.0 .500

.1 .497

.2 .457

.3 .382

.4 .307

.5 .233

.6 .195

.7 .157

.8 .118

.9 .080

1.0 .042

the first column is the ten sections you have made .0 is the opening, 1.0 is the beginning narrow part

the second column is the distance from your centerline. take these numbers and multiply by your width and plot the points from the centerline

i then connected the points amd rounded the lines out a bit to create smooth lines. when rounding the lines keep in mind that you still want to intersect your plotted points

i then cut along the lines with scissors

i traced the original onto another piece of paper so i will always have the main template.

i placed the secondary on the hood of my truck and traced it out

when you fabricate/install the unit make sure your corners going down are a crisp 90*... this will help promote air flow.

my plan is to cut on the lines with tin snips and use the metal from the hood then just fill in the sides with other sheet metal and weld all together, finish up with some body filler, then sand corners to a crisp 90*

[Master-O-Turbonics]

I just laminated and bagged one up in 3 layers of carbon fiber tonight on an old mold, but not as big as yours. Ready to go into the autoclave in the morning!

[sinner720st]

i know mine is really big. i dont really want it so big, but the scoop dictated the size...

 

when your fiber sets up you should post some pics here

[kmc63]

Wow! That is some of the most boring stuff I have ever seen on this site. Let me go get my calculator and pocket protecter.Ok where,s the wind tunnel? :P

[Skib]

Wow! That is some of the most boring stuff I have ever seen on this site. Let me go get my calculator and pocket protecter.Ok where,s the wind tunnel? :P

 

 

we did wind tunnel tests at HybridZ

 

that "boring stuff" as you call it, is engineering, and its what builds cars and then makes them stronger and faster.

 

 

 

and great write up sinner, gonna move this to the how to section.

[kmc63]

we did wind tunnel tests at HybridZ

 

that "boring stuff" as you call it, is engineering, and its what builds cars and then makes them stronger and faster.

 

 

 

and great write up sinner, gonna move this to the how to section.

Sorry,Didnt mean to upset anyone,just not a techie.

[Skib]

Sorry,Didnt mean to upset anyone,just not a techie.

 

Im just givin you crap ;)

 

esp cuz we actually did do wind tunnel testing :rofl:

[sinner720st]

thanks for the support skib... as for kmc im sure he can just break wind some other way

[Master-O-Turbonics]

untrimmed, as popped from the mold

[Skib]

untrimmed, as popped from the mold

 

 

[Master-O-Turbonics]

 

no hotlinking. :-P

[Skib]

fixed :lol:

[Master-O-Turbonics]

How much $$$ do you want it?

[sinner720st]

that is sweet looking really good job on the fiber laminating or whatev its called.

 

if only there was a way to test its flow on a hood or something while at speed... or you could have some sort of fan in a big tunnel blowing air at driving speed. i think im going to invent something like that

 

 

then test mine when its done and se if it takes more speed to really get rolling or if it flows better or worse?

 

 

 

 

 

 

 

 

[Master-O-Turbonics]

that is sweet looking really good job on the fiber laminating or whatev its called.

 

if only there was a way to test its flow on a hood or something while at speed... or you could have some sort of fan in a big tunnel blowing air at driving speed. i think im going to invent something like that

 

 

then test mine when its done and se if it takes more speed to really get rolling or if it flows better or worse?

 

 

 

You could just drive it. LOL. Just drive it on the road and use a pressure/vacuum sensor in the intake tract of the NACA duct.

[sinner720st]

thats it. seal up your air box and put a vacuum fitting in it... hope for positive pressure or at least zero vac... then put one after the carb and see if that looks any better

[Master-O-Turbonics]

I got a little crazy building carbon stuff this week...

This was from a mold for some super crazy top secret race car 5+ years ago...sitting on top of my turbo.

 

 

 

Made a second NACA duct that is a few grams heavier but at least twice as strong. Same amount of layers, just put some reinforcement in certain areas. Looks identical to the first one.

[sinner720st]

that cone is so smooth, you should do a write up on mold making and layin fiber, and all that

[Laecaon]

that cone is so smooth, you should do a write up on mold making and layin fiber, and all that

 

 

I agree. There have been so many things I have wanted to make out of Carbon Fiber. Care to share how you lay it, resin used, how you vacuum seal it, where you get your supplies?

[Master-O-Turbonics]

Used pre-impregnated carbon, about $6 a square foot per layer...

Most parts are 3+ layers. A carbon mold is ~20-40 layers of carbon.

Make a plug out of MDF, paint with this super expensive paint and wet sand until super smooth, then use mold primer($100 a gallon) to give a super slick finish. Then lay up your mold onto the MDF plug. Lots of layers... The more layers, the longer the mold will last.

Bagging process:

Once you do that, cover the part in release film, then cover in cotton breather.

Next put the part in the vacuum bag that is simply a plastic tube on a roll. Cut off the desired length of bag and seal one side with the super special double sided sticky tape thats good for high temps. Put half the bottom half of the vacuum port into the bag on top of some breather and seal the other side of the bag. Once the bag is sealed up, push the vacuum port through the bag and seal it up to the back half of the vacuum port. Now your bag should be ready to pull a vacuum on. As the vacuum is pulling the bag tight against the part, position and move the bag around on the part so that the bag is not being stretched at all.

 

 

Here is a tube I laminated and bagged on Monday. With a tube you have to do a bag inside of a bag to completely seal and properly cure the part. When they fire up the oven to bake this part, it will be cooked at 250 degrees for 60 minutes.

 

 

This process is almost identical to what is used to build F1 cars and other carbon framed-vehicles. In fact the place I do this work builds many carbon monocoque framed race cars. Vacuum bagging an open wheel chassis is done with about a 40 foot long bag and takes 2 guys about 3-4 hours just to bag.