How do you measure lift in a low-speed wind tunnel?

[dumb]

Hey,

I'm trying to measure the lift/drag of a wing in a low-speed wind tunnel, the only ways i might know are using a load cell or force probs, but have no idea about how to set it all up and my school doesn't have the material. So please, can u give me any way using simple things to measure the lift and maybe the drag as well. btw I am really really in a rush

THANX.

 

[russ_watters]

Lift is easy - just use a scale. If you attach the airfoil to several rods, run them through the bottom of the tunnel, and into a weight, you can just put the weight on a scale (or load cell) and measure the change in weight. The reason for using the weight is it provides a stable base for mounting the wing.

Drag is tougher. If you can rig up a rectancular (parallelogram) support structure, pinned at each corner and supported in the middle in a way that allows it to pivot without changing the angle of attack, the drag force on the top of the rectangle will be converted to a horizontal force in the opposite direction at the bottom. A load cell could measure the resulting force. Then set that whole rig on a scale (or another load cell) for the lift as above.

For really low-tech, a 90 degree bend in a lever arm will convert the horizontal drag force into a vertical force that can be measured on a second scale.

(I may need to draw you a picture...)

edit: http://www.aerolab.com/educational.html is an example.

 

[jdavel]

russ_waters,

"If you attach the airfoil to several rods, run them through the bottom of the tunnel, and into a weight, you can just put the weight on a scale (or load cell) and measure the change in weight."

Very elegant! And four equal length strings attached at the corners of the airfoil should maintain a constant attack angle. They would have to be attached above at adjustable heights (defined by the attack angle).

 

[rockolance]

"four equal length strings attached at the corners of the airfoil should maintain a constant attack angle. They would have to be attached above at adjustable heights (defined by the attack angle)"

I want to measure different angle of attack and lift. can you explain the spring adjustments for my experiment. i tried to find a wind tunnel for my exp but it is too costly. can you help me on how to build simple wind tunnel for my experiment. i tried googling but can't find the simple one.

 

[downersmith]

Hello
New to the forum and found this post of interest as I want to build a wind tunnel and want to find a low cost method to measure lift and drag. The post from Russ has a link to a drawing, but I think because of the date of the post it is no longer available - I did try but was not successful. Is it possible that he drawing is still available? Many thanks.

 

[magpies]

A fan and a box with some tape should do it if you want a really cheap wind tunnel.

 

[downersmith]

Thank you and I have considered this option but what I would like to do is to measure lift and drag - there are several threds in PF but I have not come across a definative method to do these measurements easily and at low (...ish) cost.

 

[downersmith]

Since my posting in this thread I have been doing a lot of research and feel that the Wind Tunnel design of John Cippolla (easily found on the internet) is a good bet. Building the tunnel is the easy part an is really only limited by the cost of the motor. The important part of the whole item is the two axis measuements of lift and drag as qualitative measurements. Cippolla design does give a good insight into a balance to do this.

Wind speed through the tunnel is best measured with a manometer and one from the Dwyer range would be good as they also have excellent pitot tubes - again, Cippola's design use these and gives details.

Another approach is Cippolla's software wind tunnel which is what I went for in the end - it works well and is a useful tool.

I hope this helps and good luck.

Regards
Douglas

 

[azeng97]

Hi, I can't exactly see the picture, would it be possible to post again? Thanks!