How can i make a simple wind tunnel apparatus for measuring lift?

I am making a wind tunnel from a fan, some cardboard, duct tape, cups and K'nex to help me design flying machines. How can i make something for measuring lift on a wing about 4 inches long? Also, would it be best to test lift and stability with low, medium or high winds.

kelseymh6 years ago
This is a very good project for an ambitious student. You can get very satisfactory results with a relatively simple system. Start with building a good wind tunnel (see our replies to your more recent question).

For measuring lift, the easiest way to do it for a do-it-yourself person is with a reasonable precision scale, like a postal scale. If you can get a true precision scale (milligrams), for example, at a chemical-supply company or from your school science teacher, that's even better.

Mount your plane on the end a thin, stiff blade (like a strip of balsa), and glue the other end to the platform of the scale. You'll want the cut the ends at an angle (make a parallelogram), so that the blade leans into the wind, and you want the angles not quite the same, so that your aircraft is positioned at the right angle of attack.

Reset the tare on the scale so that it reads zero with everything mounted. Now close up your wind tunnel and turn it on. If you are getting lift, then the scale should start to read negative values, since the lift will be pulling up on the platform. Let everything come to a steady state, and record your value. Turn off the fan, and make sure the scale goes back to zero. If it doesn't, record the discrepancy, and reset it again. Repeat this several times (at least half a dozen, preferably more than 23 for Gaussian statistics). The average and RMS of all your readings tells you the lift.

Repeat the whole process for different wind speeds, or different wing designs.
seandogue6 years ago
Use drinking straws to create a laminar flow field. It's quite simple.
orksecurity6 years ago
Doing it properly, alas, isn't quite that simple. You need to take most of the turbulence out of the airflow, or eddy currents can give you misleading results.

Many years ago, Estes published a semi-decent wind tunnel for model rockets. It started with a squirrel-cage blower, so turbulence was mostly at right angles to the airflow. Air was then directed through a honeycomb of cardboard tubes (about 2' long?), to damp out that turbulence. (This wouldn't work if the turbulance went the other way, as it would with a normal fan.) The test chamber followed this baffle. I don't remember whether there was another baffle at the back of the chamber or not.

More detailed plans might exist on line somewhere. Dropping a note to Estes might work -- they might at least be willing to sell you the back-issue of their magazine which contained those plans.