http://www.lerc.nasa.gov/WWW/K-12/ae...let/vj402.html

 

I like Xfoil. There are executable Win32 binaries available, but I've only used the compile-it-yourself Linux version.

Xfoil does not do multi-element wings. There is another program called Javafoil which does. I haven't used it much.

 

hey erik,
i saw your car at ronnie's today

it looks fantastic.

 

It's getting there It has no suspension at the moment. I'm sending that off to TC Design to have the bushings replaced with hiem joints, new adjustable front upper a-arms and new adjustable rear toe links. I'm hoping it will be done by the end of the month.

 

I wish I knew how to use these programs so I could figure out the most efficient angle of attack for my wing - though I doubt the program could take into effect the direction of the airflow aft of the hardtop

 

Xfoil or Javafoil or similar programs can give you a good idea of what is going on, but it helps to have some aerodynamics education.

However, those are what are known as 2D panel codes. They are a starting place. But actual testing on the car is going to give the real answer. Unless you are a pro racing team, it's just not worth investing in the kind of CFD that will answer this question.

As for the hardtop, the wing doesn't actually know what direction it is pointed in. It only knows what direction the wind is hitting it at. This is called the angle of attack. But the car is a 3D problem, and no 2D code can actually simulate it. You just have to use them carefully to get an idea of what is happening.

 

CFD? Cubic ****ing Dollars?

 

my Aerospace Technology degree (glorified title for pilot training through Certified Flight Instructor) has given me enough aerodynamics training to realize the angle of attack's relationship to the relative wind (which as I meant above is NOT wind that is not horizontal and undisturbed as a result of the hardtop)

even if i could figure out how to use the software to get a rough estimation, i would not know how to test the variable geometry that the J's wing has about the chord-line (thinner and lower at the tips)

seems trial and error with a Data Logger is the best option for optimizing the angle of attack at our level...

 

Some tape, wool tufts and a camera?

 

that will give you an idea to determine if the wind is flowing past the airfoil smoothly, but smooth airflow around the airfoil does not necessary indicate whether that is the maximum downforce that can be generated...

one thing is for sure though, max downforce is not achieved by setting the highest angle of attack - as amateur racers often do...