Wing Design

[deleted-24807]

What is the correct way to build a wind tunnel to test various wing designs? At what location on the wing designs do I put the supports to test lift on each?

[deleted-71588]

What is the correct way to build a wind tunnel to test various wing designs? At what location on the wing designs do I put the supports to test lift on each?

There "IS" no "ONE" "CORRECT" way to do things!
Have you done any reasearch (reading) on how others have approached this to get some ideas? Have you done any research into the issues involved in making these measurements?

What are you really trying to measure lift on? Is it just a piece of a wing or is it a scale model of an entire plane? You are entering the area of fluid dynamics which is characterized by figuring out a lot of boundary conditions. Anything you add mechanically to a setup will add additional boundary conditions that will affect your results in some way to some extent. Your goal should be to come up with ways of reducing the effect of your additions to be less of a factor than what you are attempting to measure.

[deleted-24807]

I have done research on how to build a wind tunnel but I just can't find a good explanation. Could you point me in the right direction? How do I build the tunnel so that it produces a good laminar flow? What should the tunnel be made out of? I'm trying to measure the lift of just a piece of a wing using a scale. Do you recommend using a common digital bathroom scale or something else?

[paulsdecarli]

In my model airplane days (1937-1942), we used a few boxes of soda straws packed together at the entrance to the wind tunnel. Our thought was that the air going through the length of the soda straws would come out laminar. We also used smoke to show the air flow around our wing sections (and help judge the quality of laminar flow). One needs to have transparent sides to the tunnel for that. One way to measure lift was simply to attach weights until lift was neutralized. One requirement for wing support is that it has to maintain angle of attack while allowing wing to rise (so that the weights can balance the lift). It would actually be a fairly good project just to design a wind tunnel setup so you could show how you solved the problems. The testing of wing sections could be done as the next year's project.

[deleted-24807]

What do you recommend using for construction of the airfoils? Foam, sheets of clear plastic, etc.? I couldn't find any sugestions online.
Also I'm a little confused about how and where to put the weights on the airfoil to measure lift. I couldn't find that either.
If anyone can help that would be great!

[deleted-71631]

Codeman:
I built a wind tunnel while in high school and I can tell you from first hand experience that this was a difficult and time-consuming task to design, fabricate, and debug. As noted in an earlier post, it helps to have transparent sides and sheet plexiglass (appro. 1/8" thick) is what I used. If you're starting to do this project now, completing a wind tunnel and gathering results will be quite challenging in the time remaining this year. Not impossible, but only possible with substantial assistance and the proper equipment. Measuring lift will also be a tricky proposition involving fairly precise measurement devices, and these are not easy to do. I have an alternate suggestion.

It'd be easier to construct a water flow device where a "sheet" of water flows around airfoils that could be made out of, for example, waterproofed balsa wood or foam. A fairly low velocity of water will show many of the flow characteristics that are also present at higher airspeeds (an example of the "Reynolds Number" effect where water's increased viscosity and density allows lower flow speeds to replicate the same Reynolds number and associated flow effects).

The water could flow through a channel and test section and from there, exit into a drain. Constructing this channel and test section should be much easier than designing and building a fan-driven "air" wind tunnel. While it would not be practical to try to measure lift or drag forces, you could use an eyedropper to put single drops of food dye into the flow - and thus be able to photograph when separation occurs for different airfoils as you vary angle of attack. Sample test articles could be flat plates, blunt bodies, spheres, or airfoils.

You will need to compose a hypothesis that you would then prove or disprove using this type of test device. You will need to determine your dependent and independent variables, and there's ample discussion of these terms, plus proper test design, in the Science Buddies reference sections that you should read.

Good luck!
Peter Young