Building a mini-wind tunnel

[Rasori]

I plan to build a miniature wind tunnel, a lot like the Wright Brothers' used in 1901. I have stabilization (of model and air currents) all set up, I just have one problem- I have no devices to measure lift or drag.

 

The site I went to (don't have a link, but if you just google up "wright brothers wind tunnel" you'll find it) mentioned that they used old hack saw blades and other things lying aroung to make their devices. My assumption was that they used a spring that was calibrated so that each increment would equal a notch on the hack saw blade. I want to look into making instruments that could do this or just find out what modern-day equivalents we have that will work.

 

As for my assumption, basically I assumed that the lift device was on the bottom. They had a little marker that pointed where the spring was, and a string that connected to a hook in the bottom of the model (or some other connector). When lift was created, the model would rise and pull the spring up as well. And for drag, I assumed the same thing, except the device was on its side. I'm sure that's a MUCH too simplistic point of view and I'm almost positive it's not at all true, but if it's somewhat possible (I know there are spring scales that could probably be used a similar way) then please inform me

[Rasori]

Oh, one other thing! I nearly forgot. Wind tunnels tend to use smoke to show air travel patterns. I could use smoke both to make sure that my wind isn't turbulent and to see the air currents. So, does anyone have suggestions for a safe and at least semi-controllable smoke releaser (or smoke bomb, your choice lol).

[Nave]

smoke bomb sounds good...make sure the color of ur smoke contrasts the background so u can get a good look at it...also another idea if u can get any free or buy cans of air if u turn them upside down and spray them u get a white stream coming out but i dont know how long ur wind tunnel is so check it out before u get many cans of air...

[Lance]

How save do you want it to be? Find a heating element and put it in a heat resistant container then just fill it with mineral oil.

[Rasori]

I want it safe enough to not kill/hurt me and keep the wind tunnel in-tact. Sorry, too safe?

[J.C.MacSwell]

I have a small (cross section 30" X 20") wind tunnel that is low speed (30 ft/s). For drag I use elastic from inside a bungy cord. I calibrated it and it was not linear (didn't follow Hooke's law) but it was reasonably consistent for crude measurements. For visualization I reach in with a wool tuft "tickler" on a coat hanger.I would like to use smoke at some point.

[Guest CrazyJohn]

A very simple way of generating smoke in a small scale wind tunnel is to burn some incense sticks in the upstream flow. You could also try burning some wet/rotten wood and capturing the resulting smoke then using the venturi effect of the tunnel flow to draw the smoke into the tunnel through a suitably placed tube, note the disadvantage of this is that repeated use will result in the accumulation of tars on your model and the surfaces of the tunnel, it also an eye irritant so may not be that much fun.

 

Other means are a bit more involved and generally require the use of what is known as a "Preston-Sweeting mist generator." This basically requires the forcing of a suitable liquid (usually kerosene or liquid paraffin) through a narrow tube that has a heating element surrounding it. The oil vaporises in the tubing and then passes into a larger space, causing the oil vapor to quickly condense to form a visible white smoke. This is then drawn into the tunnel for testing.

[Guest CrazyJohn]

You should note: the heating of kerosene or any other flammable liquid is potentially dangerous and should only be undertaken by skilled persons.