Building a wind tunnel

[littleport2003]

Hi Guys,

I'm planning to build a wnd tunnel, but I've got a few questions:
1. whats the best type of fan to use, ducted fans for RC jets are a bit to small for me, would just a normal prop from a plane work?
2. what should I use to make the lines of smoke, a fog machine seems like overkill to me.

Thanks, Matt

[Sparky Paul]

What do you want it to do?
A smoke tunnel can give you views of airflow.
A wind tunnel which measures lift and drag requires a very sophisiticated installation of the mount and the lift and drag sensors. A kitchen scale won't do it.
Both need well-controlled airflow.
You might google on the subject.. there are private/personal wind tunnels around..
The University of Illinois might have useable information.
Michael Selig works there.

[ghoti]

http://www.first-to-fly.com/Adventure/Workshop/1901_wind_tunnel.htm

[ghoti]

I think you can use a few hundred soda straws bundled in parallel to smooth the airflow in a wind tunnel. Bill

[hoppy]

http://www.theplanpage.com/Months/2306/tunnel_files/tunnel.pdf

[BMatthews]

If you're going to make a wind tunnel you need to figure out what you want it to do for you. Also you need to understand that if you're going to do airfoil or turbulence testing that these are two totally different requirements. But either way you need to make it a lot larger than you think you need. It's important to the test results that the tunnel cross section be a lot larger than the test model in order to avoid any compressive complications of the walls on the model under test. So if you want to test a model with a 1 to 1.5 foot wingspan you pretty much need something that is at lest 4 foot wide by 4 foot tall AT LEAST to avoid any wall reflections or compressive "ground effect" type complications.

When you start talking about that size of tunnel your motor ends up being something more like a 1/2 to 3/4 HP electric motor and your fan is a big multibladed deal that you can make up from a center plate and some jumbo scale single blades mounted into the hub plates and filler.

[ghoti]

Wilber and Orville made wings about 6 inches span for their tunnel tests. Thst sounds about right for the accuracy vs. wind tunnel size reduction tradeoff.
Bill

[Accu157]

Perhaps there are some starting guidelines that apply well to most DIY windtunnels?

Maybe a couple of box-fans will do? Box-fan enclosures, run a different motor? Might enable you to tear-apart the wind tunnel for storage.

[ghoti]

Well, "boxfan" anything like a muffen fan (300CFM) or (Less desirable) a whisper fan (100CFM), generic things about 5 or 6 inches square?

That would be a start. With that low flow rate you could use simple paper cutout model surfaces and observe things like how far things move and in which direction. All experiments succeed, one way or another, in learning experience

But for more serious studies I would go for vacuum cleaner power levels, up to 1 HP. That would present some challanges and opportunities for learning.

Hack it together with duct tape and go for it! Share the results. Bill

[JonB]

In the late 1950's, I built a successful wind tunnel (actually a smoke tunnel if you will). It was powered by a surplus (Mom's extra) vaccuum cleaner motor and blower assy, using a butterfly baffle to control the flow. The smoke was "generated" the same way that the "Lionel" trains did it- a nichrome wire (from a toaster) submereged in a quart glass jar of mineral oil (use a transformer to step down voltage and experiment to get the proper length). The smoke was transfererd via a hose to a streamlined manifold that had maybe 30 brass tubes evenly spaced to dispurse the smoke. The actual airflow channel was made from plexiglass and used back lighting, the remainder being plywood. Using a generic airfoil to fit the channel and about 6.0" long mounted on a shaft that allowed changes in Angle of Attack. It was certainly amazing to see the lines of laminar flow change with the varying conditions..including stalled....I won the science fair that I had entered. Plans for a similar wind tunnel were published in Model Airplane News in the late 50's.or early 1960's. Perhaps they can help locate the article and plans. If I can be of further help..let me know.. Regards,
Jon B. Shereshaw, NJ. USA

[Accu157]

Well, "boxfan" anything like a muffen fan (300CFM) or (Less desirable) a whisper fan (100CFM), generic things about 5 or 6 inches square?
Bill

:)

I was thinking a little bigger. Maybe a round fan at the exit too, this one isn't too bad, I don't know how the stator deal would work to keep the air from making a vortex. Just, keep it far from the wind tunnel portion?

1500 CFM:
http://www.northerntool.com/webapp/wcs/stores/servlet/product2_6970_754509_754509

various types:
http://www.northerntool.com/webapp/wcs/stores/servlet/category2_6970_867+126

perhaps some kind of resistor would help adjust wind flow?