Lift and Drag force in a Wind Tunnel

[Kart]

Hello guys,
I am trying to calculate the lift force and drag force in a wind tunnel at my school as a part of a project that i am doing. I am varying the length of the airfoils and trying to measure the lift force and drag force.

I have 3-d printed 7 airfoils. However, I am not able to find any method through which i can collect data in the wind tunnel. I tried using a force sensor but it failed as the airfoil couldn't stay stable. Can you guys help me on this? Can you guys provide any method through which I can collect data for this. Any help would be appreciated as I am pressed on time!

The Wind tunnel is a typical Sub-sonic wind tunnel.
The airfoils have a hole in the end which i thought I could use for measuring drag force. However, it wasn't stable at all.

 

[anorlunda]

That sounds interesting. But I don't understand how there is anything to measure if the airfoil can't stay stable. What do you mean by can't stay stable?

 

[FactChecker]

Are you mounting it one of these ways? https://www.grc.nasa.gov/www/k-12/airplane/tunbalmnt.html
It should be mounted rigidly where strain gages can measure the forces (lift, drag, side) and moments (pitch, roll, yaw).

 

[Kart]

@anorlunda whenever I put the airfoil inside the test section, it always turned 90 degrees to the side eventually. So I guess what I want is a way to either keep the airfoil still so that the angle of attack is constant and the airfoil doesn't rotates to the side or another way of measuring lift force and drag force which doesn't include wind tunnels at all

 

[Kart]

@FactChecker Yeah that's the problem. It isn't rigid at all! I have tried putting clay around it to make it rigid but didn't work. Is there any other way I can make it rigid. The reason why it is not rigid is because the hole in the airfoil is a bit bigger than the rod.

 

[Kart]

I am also considering building another set of airfoils by using thermocol and a hot wire foam cutter. I believe this would remain more stable and won't rotate in the Wind Tunnel. Is this a good idea?

 

[FactChecker]

It must be mounted on something that will hold it in place AND measure the force required to hold it in place. You can not separate those two functions. And it should disturb the airflow around the model as little as possible.

 

[Kart]

@FactChecker Yep I used a dual range Vernier Force sensor for that purpose.

 

[CWatters]

Not clear what's causing your wing to rotate but perhaps look up pitching moment.

 

[FactChecker]

I think you should tell us which forces and moments you are measuring, if not all. And you need to adequately describe your current mount. Are you using one of the mounts in the NASA link in post #3?

 

[boneh3ad]

The bottom line here is that any airfoil at an angle of attack is going to have not only forces (lift and drag) on it, but a pitching moment as a result of those forces. The mounting system used must be able to counteract both of these effects in order to prevent the airfoil from moving.

Now, the explanations so far have been quite vague in terms of where this "hole" in the airfoil is and how it is mounted, so I am not sure we can really give any ideas to help solve the problem without more indication of what the problem actually is. Perhaps a picture or photo would be useful.