Simple lift/drag measurements in a wind tunnel

[09matthew]

Hi everyone,

I will be conducting wind tunnel tests of a NACA 0012 airfoil to obtain values of lift and drag in a low-speed wind tunnel (approx M = 0.1). I am looking for a really simple way of measuring these forces. Does anyone know of ways to achieve this?

I am aware of force balance techniques but I do not really know how to set it up and there is no experience of this at my school.

Thank you!

 

[jim hardy]

did you study how the Wright Brothers did it ?

https://wright.nasa.gov/airplane/balanceo.html

 

[Ranger Mike]

A diffuser pump is really just a small mini wing (large radius in front small radius on back side. Its purpose was to direct the flow of under car air to blend in and combine with the air coming off the lower wing of the dual rear wing. The diffuser pump is attached at the rear most diffuser, slightly elevated. The wing attack angle is adjustable. Now the question is how do you get best performance out of it when you are garaged in acorn field in west Ohio?
Any good engineering guy knows you have to identify the problem. Brain storm and make a plan. execute it . follow up with feed back and repeat above til it hurts or is fixed. We needed a force to replicate wind over the car surface. Shop vacuums can blow as well as suck so we got a couple of them. Next, we needed several means to determine the best flow. So we made a manometer. A long piece of vinyl tubing placed on a clip board that had graph paper as a tow axis scale was rigged up. we filled it with a small amount of Scope mouth wash to make it more visible. one tube ended in a 90 degree bend and left open to the atmosphere the other end was to be placed in the flow stream to measure air speed. We sent the fat neighbor boy to the carry out for a much needed six pack and while he drove we rode along with the clip board and tune duct taper to the top of rear view side mirror. We penciled a line on the graph paper every 10 MPH. It worked pretty good. More to come on this later.

 

[Ranger Mike]

We rigged up a shop vacuum cleaners to blow air over the top of the rear diffuser and under it. A diffuser is an air foil device covering the bottom side of the race car. It is curved at the rear so the air exiting under the car would take an upward path and exit pointed at an upward angle. This created down force. Bernoulli effect. By taping tufts of yarn at various points on the underside and top side of the diffuser and lower wind element we could see the flow without the diffuser pump the after the diffuser pump and finally the flow at best attack angle of the little mini wing. We made a height stand and taped yarn tufts every 3 inches so we could see the flow right off the lower rear wing and a foot from the rear wing. We did the same at exit points on the car.We needed to back up the manometer readings with some other measurable way to get a solid repeatable number. A metal plate and dial indicator on the magnetic stand would be the gage and a thin piece of aluminum sheet with a duct tape hinge would prove quite repeatable when placed in the wind stream. As we dialed in the proper attack angle the reading dropped on the under diffuser flow and the stream blended in with the air coming off the top of the diffuser.

 

[Ranger Mike]

So the photos show the good flow as noted by the number of tufts streaming on the height stand furthest from the wing. Note the number of tufts not floating in air. Only two are really flying straight out.
Then note the 8 tufts flying in the air stream on the final best flow pic. We got the tow streams blending and combining to reduce drag and increase down force.
Bottom line is that you can do a lot with what you got on hand ifin you think about it.

 

[boneh3ad]

Hi everyone,

I will be conducting wind tunnel tests of a NACA 0012 airfoil to obtain values of lift and drag in a low-speed wind tunnel (approx M = 0.1). I am looking for a really simple way of measuring these forces. Does anyone know of ways to achieve this?

I am aware of force balance techniques but I do not really know how to set it up and there is no experience of this at my school.

Thank you!

Without a force balance handy, you have some other options, but it would be helpful to know what your school has available already. Doing things like this isn't generally cheap.